Physics II The Electromagnetic Spectrum Learning Objectives By the end of this section you will be able to List three rules of thumb that apply to the different frequencies along the electromagnetic spectrum Explain why the higher the frequency the shorter the wavelength of an electromagnetic wave Draw a simplified electromagnetic spectrum indicating the relative positions frequencies and spacing of the different types of radiation bands List and explain the different methods by which electromagnetic waves are produced across the spectrum In this module we examine how electromagnetic waves are classified into categories such as radio infrared ultraviolet and so on so that we can understand some of their similarities as well as some of their differences We will also find that there are many connections with previously discussed topics such as wavelength and resonance A brief overview of the production and utilization of electromagnetic waves is found in Table 1 Table 1 Electromagnetic Waves Type of EM wave Production Applications Life sciences aspect Issues Radio TV Accelerating charges Communications remote controls MRI Requires controls for band use Microwaves Accelerating charges thermal agitation Communications ovens radar Deep heating Cell phone use Infrared Thermal agitations electronic transitions Thermal imaging heating Absorbed by atmosphere Greenhouse effect Visible light Thermal agitations electronic transitions All pervasive Photosynthesis Human vision Ultraviolet Thermal agitations electronic transitions Sterilization Cancer control Vitamin D production Ozone depletion Cancer causing Xrays Inner electronic transitions and fast collisions Medical Security Medical diagnosis Cancer therapy Cancer causing Gamma rays Nuclear decay Nuclear medicine Security Medical diagnosis Cancer therapy Cancer causing Radiation damage Connections Waves There are many types of waves such as water waves and even earthquakes Among the many shared attributes of waves are propagation speed frequency and wavelength These are always related by the expression v W fλ This module concentrates on EM waves but other modules contain examples of all of these characteristics for sound waves and submicroscopic particles As noted before an electromagnetic wave has a frequency and a wavelength associated with it and travels at the speed of light or c The relationship among these wave characteristics can be described by v W fλ where v W is the propagation speed of the wave f is the frequency and λ is the wavelength Here v W c so that for all electromagnetic waves c fλ Thus for all electromagnetic waves the greater the frequency the smaller the wavelength Figure 1 shows how the various types of electromagnetic waves are categorized according to their wavelengths and frequenciesthat is it shows the electromagnetic spectrum Many of the characteristics of the various types of electromagnetic waves are related to their frequencies and wavelengths as we shall see Figure 1 The electromagnetic spectrum showing the major categories of electromagnetic waves The range of frequencies and wavelengths is remarkable The dividing line between some categories is distinct whereas other categories overlap Electromagnetic Spectrum Rules of Thumb Three rules that apply to electromagnetic waves in general are as follows Highfrequency electromagnetic waves are more energetic and are more able to penetrate than lowfrequency waves Highfrequency electromagnetic waves can carry more information per unit time than lowfrequency waves The shorter the wavelength of any electromagnetic wave probing a material the smaller the detail it is possible to resolve Note that there are exceptions to these rules of thumb Transmission Reflection and Absorption What happens when an electromagnetic wave impinges on a material If the material is transparent to the particular frequency then the wave can largely be transmitted If the material is opaque to the frequency then the wave can be totally reflected The wave can also be absorbed by the material indicating that there is some interaction between the wave and the material such as the thermal agitation of molecules Of course it is possible to have partial transmission reflection and absorption We normally associate these properties with visible light but they do apply to all electromagnetic waves What is not obvious is that something that is transparent to light may be opaque at other frequencies For example ordinary glass is transparent to visible light but largely opaque to ultraviolet radiation Human skin is opaque to visible lightwe can not see through peoplebut transparent to Xrays Radio and TV Waves The broad category of radio waves is defined to contain any electromagnetic wave produced by currents in wires and circuits Its name derives from their most common use as a carrier of audio information ie radio The name is applied to electromagnetic waves of similar frequencies regardless of source Radio waves from outer space for example do not come from alien radio stations They are created by many astronomical phenomena and their study has revealed much about nature on the largest scales There are many uses for radio waves and so the category is divided into many subcategories including microwaves and those electromagnetic waves used for AM and FM radio cellular telephones and TV Figure 2 This highvoltage traction power line running to Eutingen Railway Substation in Germany radiates electromagnetic waves with very long wavelengths credit Zonk43 Wikimedia Commons The lowest commonly encountered radio frequencies are produced by highvoltage AC power transmission lines at frequencies of 50 or 60 Hz See Figure 2 These extremely long wavelength electromagnetic waves about 6000 km are one means of energy loss in longdistance power transmission There is an ongoing controversy regarding potential health hazards associated with exposure to these electromagnetic fields E fields Some people suspect that living near such transmission lines may cause a variety of illnesses including cancer But demographic data are either inconclusive or simply do not support the hazard theory Recent reports that have looked at many European and American epidemiological studies have found no increase in risk for cancer due to exposure to E fields Extremely low frequency ELF radio waves of about 1 kHz are used to communicate with submerged submarines The ability of radio waves to penetrate salt water is related to their wavelength much like ultrasound penetrating tissuethe longer the wavelength the farther they penetrate Since salt water is a good conductor radio waves are strongly absorbed by it and very long wavelengths are needed to reach a submarine under the surface See Figure 3 Figure 3 Very long wavelength radio waves are needed to reach this submarine requiring extremely low frequency signals ELF Shorter wavelengths do not penetrate to any significant depth AM radio waves are used to carry commercial radio signals in the frequency range from 540 to 1600 kHz The abbreviation AM stands for amplitude modulation which is the method for placing information on these waves See Figure 4 A carrier wave having the basic frequency of the radio station say 1530 kHz is varied or modulated in amplitude by an audio signal The resulting wave has a constant frequency but a varying amplitude A radio receiver tuned to have the same resonant frequency as the carrier wave can pick up the signal while rejecting the many other frequencies impinging on its antenna The receivers circuitry is designed to respond to variations in amplitude of the carrier wave to replicate the original audio signal That audio signal is amplified to drive a speaker or perhaps to be recorded Figure 4 Amplitude modulation for AM radio a A carrier wave at the stations basic frequency b An audio signal at much lower audible frequencies c The amplitude of the carrier is modulated by the audio signal without changing its basic frequency FM Radio Waves Figure 5 Frequency modulation for FM radio a A carrier wave at the stations basic frequency b An audio signal at much lower audible frequencies c The frequency of the carrier is modulated by the audio signal without changing its amplitude FM radio waves are also used for commercial radio transmission but in the frequency range of 88 to 108 MHz FM stands for frequency modulation another method of carrying information See Figure 5 Here a carrier wave having the basic frequency of the radio station perhaps 1051 MHz is modulated in frequency by the audio signal producing a wave of constant amplitude but varying frequency Since audible frequencies range up to 20 kHz or 0020 MHz at most the frequency of the FM radio wave can vary from the carrier by as much as 0020 MHz Thus the carrier frequencies of two different radio stations can not be closer than 0020 MHz An FM receiver is tuned to resonate at the carrier frequency and has circuitry that responds to variations in frequency reproducing the audio information FM radio is inherently less subject to noise from stray radio sources than AM radio The reason is that amplitudes of waves add So an AM receiver would interpret noise added onto the amplitude of its carrier wave as part of the information An FM receiver can be made to reject amplitudes other than that of the basic carrier wave and only look for variations in frequency It is thus easier to reject noise from FM since noise produces a variation in amplitude Television is also broadcast on electromagnetic waves Since the waves must carry a great deal of visual as well as audio information each channel requires a larger range of frequencies than simple radio transmission TV channels utilize frequencies in the range of 54 to 88 MHz and 174 to 222 MHz The entire FM radio band lies between channels 88 MHz and 174 MHz These TV channels are called VHF for very high frequency Other channels called UHF for ultra high frequency utilize an even higher frequency range of 470 to 1000 MHz The TV video signal is AM while the TV audio is FM Note that these frequencies are those of free transmission with the user utilizing an oldfashioned roof antenna Satellite dishes and cable transmission of TV occurs at significantly higher frequencies and is rapidly evolving with the use of the highdefinition or HD format Example 1 Calculating Wavelengths of Radio Waves Calculate the wavelengths of a 1530kHz AM radio signal a 1051MHz FM radio signal and a 190GHz cell phone signal Strategy The relationship between wavelength and frequency is c fλ where c 300 10 8 ms is the speed of light the speed of light is only very slightly smaller in air than it is in a vacuum We can rearrange this equation to find the wavelength for all three frequencies Solution Rearranging gives λ c f For the f 1530 kHz AM radio signal λ 300 10 8 ms 1530 10 3 cycless 196 m λ 196 m For the f 1051 MHz FM radio signal λ 300 10 8 ms 1051 10 6 cycless 285 m λ 285 m And for the f 190 GHz cell phone λ 300 10 8 ms 190 10 9 cycless 0158 m λ 0158 m Discussion These wavelengths are consistent with the spectrum in Figure 1 The wavelengths are also related to other properties of these electromagnetic waves as we shall see The wavelengths found in the preceding example are representative of AM FM and cell phones and account for some of the differences in how they are broadcast and how well they travel The most efficient length for a linear antenna such as discussed in Production of Electromagnetic Waves is λ 2 half the wavelength of the electromagnetic wave Thus a very large antenna is needed to efficiently broadcast typical AM radio with its carrier wavelengths on the order of hundreds of meters One benefit to these long AM wavelengths is that they can go over and around rather large obstacles like buildings and hills just as ocean waves can go around large rocks FM and TV are best received when there is a line of sight between the broadcast antenna and receiver and they are often sent from very tall structures FM TV and mobile phone antennas themselves are much smaller than those used for AM but they are elevated to achieve an unobstructed line of sight See Figure 6 Figure 6 a A large tower is used to broadcast TV signals The actual antennas are small structures on top of the towerthey are placed at great heights to have a clear line of sight over a large broadcast area credit Ozizo Wikimedia Commons b The NTT Dokomo mobile phone tower at Tokorozawa City Japan credit tokoroten Wikimedia Commons Radio Wave Interference Astronomers and astrophysicists collect signals from outer space using electromagnetic waves A common problem for astrophysicists is the pollution from electromagnetic radiation pervading our surroundings from communication systems in general Even everyday gadgets like our car keys having the facility to lock car doors remotely and being able to turn TVs on and off using remotes involve radiowave frequencies In order to prevent interference between all these electromagnetic signals strict regulations are drawn up for different organizations to utilize different radio frequency bands One reason why we are sometimes asked to switch off our mobile phones operating in the range of 19 GHz on airplanes and in hospitals is that important communications or medical equipment often uses similar radio frequencies and their operation can be affected by frequencies used in the communication devices For example radio waves used in magnetic resonance imaging MRI have frequencies on the order of 100 MHz although this varies significantly depending on the strength of the magnetic field used and the nuclear type being scanned MRI is an important medical imaging and research tool producing highly detailed two and threedimensional images Radio waves are broadcast absorbed and reemitted in a resonance process that is sensitive to the density of nuclei usually protons or hydrogen nuclei The wavelength of 100MHz radio waves is 3 m yet using the sensitivity of the resonant frequency to the magnetic field strength details smaller than a millimeter can be imaged This is a good example of an exception to a rule of thumb in this case the rubric that details much smaller than the probes wavelength can not be detected The intensity of the radio waves used in MRI presents little or no hazard to human health Microwaves Microwaves are the highestfrequency electromagnetic waves that can be produced by currents in macroscopic circuits and devices Microwave frequencies range from about 10 9 Hz to the highest practical LC resonance at nearly 10 12 Hz Since they have high frequencies their wavelengths are short compared with those of other radio waveshence the name microwave Microwaves can also be produced by atoms and molecules They are for example a component of electromagnetic radiation generated by thermal agitation The thermal motion of atoms and molecules in any object at a temperature above absolute zero causes them to emit and absorb radiation Figure 7 An image of Sif Mons with lava flows on Venus based on Magellan synthetic aperture radar data combined with radar altimetry to produce a threedimensional map of the surface The Venusian atmosphere is opaque to visible light but not to the microwaves that were used to create this image credit NSSDC NASAJPL Since it is possible to carry more information per unit time on high frequencies microwaves are quite suitable for communications Most satellitetransmitted information is carried on microwaves as are landbased longdistance transmissions A clear line of sight between transmitter and receiver is needed because of the short wavelengths involved Radar is a common application of microwaves that was first developed in World War II By detecting and timing microwave echoes radar systems can determine the distance to objects as diverse as clouds and aircraft A Doppler shift in the radar echo can be used to determine the speed of a car or the intensity of a rainstorm Sophisticated radar systems are used to map the Earth and other planets with a resolution limited by wavelength See Figure 7 The shorter the wavelength of any probe the smaller the detail it is possible to observe Heating with Microwaves How does the ubiquitous microwave oven produce microwaves electronically and why does food absorb them preferentially Microwaves at a frequency of 245 GHz are produced by accelerating electrons The microwaves are then used to induce an alternating electric field in the oven Water and some other constituents of food have a slightly negative charge at one end and a slightly positive charge at one end called polar molecules The range of microwave frequencies is specially selected so that the polar molecules in trying to keep orienting themselves with the electric field absorb these energies and increase their temperaturescalled dielectric heating The energy thereby absorbed results in thermal agitation heating food and not the plate which does not contain water Hot spots in the food are related to constructive and destructive interference patterns Rotating antennas and food turntables help spread out the hot spots Another use of microwaves for heating is within the human body Microwaves will penetrate more than shorter wavelengths into tissue and so can accomplish deep heating called microwave diathermy This is used for treating muscular pains spasms tendonitis and rheumatoid arthritis TakeHome ExperimentMicrowave Ovens Look at the door of a microwave oven Describe the structure of the door Why is there a metal grid on the door How does the size of the holes in the grid compare with the wavelengths of microwaves used in microwave ovens What is this wavelength Place a glass of water about 250 ml in the microwave and heat it for 30 seconds Measure the temperature gain the ΔT Assuming that the power output of the oven is 1000 W calculate the efficiency of the heattransfer process Remove the rotating turntable or moving plate and place a cup of water in several places along a line parallel with the opening Heat for 30 seconds and measure the ΔT for each position Do you see cases of destructive interference Microwaves generated by atoms and molecules far away in time and space can be received and detected by electronic circuits Deep space acts like a blackbody with a 27 K temperature radiating most of its energy in the microwave frequency range In 1964 Penzias and Wilson detected this radiation and eventually recognized that it was the radiation of the Big Bangs cooled remnants Infrared Radiation The microwave and infrared regions of the electromagnetic spectrum overlap see Figure 1 Infrared radiation is generally produced by thermal motion and the vibration and rotation of atoms and molecules Electronic transitions in atoms and molecules can also produce infrared radiation The range of infrared frequencies extends up to the lower limit of visible light just below red In fact infrared means below red Frequencies at its upper limit are too high to be produced by accelerating electrons in circuits but small systems such as atoms and molecules can vibrate fast enough to produce these waves Water molecules rotate and vibrate particularly well at infrared frequencies emitting and absorbing them so efficiently that the emissivity for skin is e 097 in the infrared Nightvision scopes can detect the infrared emitted by various warm objects including humans and convert it to visible light We can examine radiant heat transfer from a house by using a camera capable of detecting infrared radiation Reconnaissance satellites can detect buildings vehicles and even individual humans by their infrared emissions whose power radiation is proportional to the fourth power of the absolute temperature More mundanely we use infrared lamps some of which are called quartz heaters to preferentially warm us because we absorb infrared better than our surroundings The Sun radiates like a nearly perfect blackbody that is it has e 1 with a 6000 K surface temperature About half of the solar energy arriving at the Earth is in the infrared region with most of the rest in the visible part of the spectrum and a relatively small amount in the ultraviolet On average 50 percent of the incident solar energy is absorbed by the Earth The relatively constant temperature of the Earth is a result of the energy balance between the incoming solar radiation and the energy radiated from the Earth Most of the infrared radiation emitted from the Earth is absorbed by CO 2 and H 2 O in the atmosphere and then radiated back to Earth or into outer space This radiation back to Earth is known as the greenhouse effect and it maintains the surface temperature of the Earth about 40ºC higher than it would be if there is no absorption Some scientists think that the increased concentration of CO 2 and other greenhouse gases in the atmosphere resulting from increases in fossil fuel burning has increased global average temperatures Visible Light Visible light is the narrow segment of the electromagnetic spectrum to which the normal human eye responds Visible light is produced by vibrations and rotations of atoms and molecules as well as by electronic transitions within atoms and molecules The receivers or detectors of light largely utilize electronic transitions We say the atoms and molecules are excited when they absorb and relax when they emit through electronic transitions Figure 8 shows this part of the spectrum together with the colors associated with particular pure wavelengths We usually refer to visible light as having wavelengths of between 400 nm and 750 nm The retina of the eye actually responds to the lowest ultraviolet frequencies but these do not normally reach the retina because they are absorbed by the cornea and lens of the eye Red light has the lowest frequencies and longest wavelengths while violet has the highest frequencies and shortest wavelengths Blackbody radiation from the Sun peaks in the visible part of the spectrum but is more intense in the red than in the violet making the Sun yellowish in appearance Figure 8 A small part of the electromagnetic spectrum that includes its visible components The divisions between infrared visible and ultraviolet are not perfectly distinct nor are those between the seven rainbow colors Living thingsplants and animalshave evolved to utilize and respond to parts of the electromagnetic spectrum they are embedded in Visible light is the most predominant and we enjoy the beauty of nature through visible light Plants are more selective Photosynthesis makes use of parts of the visible spectrum to make sugars Example 2 Integrated Concept Problem Correcting Vision with Lasers During laser vision correction a brief burst of 193nm ultraviolet light is projected onto the cornea of a patient It makes a spot 080 mm in diameter and evaporates a layer of cornea 030 μ m thick Calculate the energy absorbed assuming the corneal tissue has the same properties as water it is initially at 34ºC Assume the evaporated tissue leaves at a temperature of 100ºC Strategy The energy from the laser light goes toward raising the temperature of the tissue and also toward evaporating it Thus we have two amounts of heat to add together Also we need to find the mass of corneal tissue involved Solution To Figure out the heat required to raise the temperature of the tissue to 100ºC we can apply concepts of thermal energy We know that Q mc ΔT where Q is the heat required to raise the temperature Δ T is the desired change in temperature m is the mass of tissue to be heated and c is the specific heat of water equal to 4186 JkgK Without knowing the mass m at this point we have Q m 4186 JkgK100ºC34ºC m 276276 Jkg m 276 kJkg The latent heat of vaporization of water is 2256 kJkg so that the energy needed to evaporate mass m is Q v mL v m 2256 kJkg To find the mass m we use the equation ρ m V where ρ is the density of the tissue and V is its volume For this case m ρ V 1000 kgm 3 area thickness m 3 1000 kgm 3 π 080 10 3 m 2 4 030 10 6 m 0151 10 9 kg m ρ 0151 kg Therefore the total energy absorbed by the tissue in the eye is the sum of Q and Q v Q tot m c ΔT L v 0151 10 9 kg276 kJkg 2256 kJkg 382 10 9 kJ Discussion The lasers used for this eye surgery are excimer lasers whose light is well absorbed by biological tissue They evaporate rather than burn the tissue and can be used for precision work Most lasers used for this type of eye surgery have an average power rating of about one watt For our example if we assume that each laser burst from this pulsed laser lasts for 10 ns and there are 400 bursts per second then the average power is Q tot 400 150 mW Optics is the study of the behavior of visible light and other forms of electromagnetic waves Optics falls into two distinct categories When electromagnetic radiation such as visible light interacts with objects that are large compared with its wavelength its motion can be represented by straight lines like rays Ray optics is the study of such situations and includes lenses and mirrors When electromagnetic radiation interacts with objects about the same size as the wavelength or smaller its wave nature becomes apparent For example observable detail is limited by the wavelength and so visible light can never detect individual atoms because they are so much smaller than its wavelength Physical or wave optics is the study of such situations and includes all wave characteristics TakeHome Experiment Colors That Match When you light a match you see largely orange light when you light a gas stove you see blue light Why are the colors different What other colors are present in these Ultraviolet Radiation Ultraviolet means above violet The electromagnetic frequencies of ultraviolet radiation UV extend upward from violet the highestfrequency visible light Ultraviolet is also produced by atomic and molecular motions and electronic transitions The wavelengths of ultraviolet extend from 400 nm down to about 10 nm at its highest frequencies which overlap with the lowest Xray frequencies It was recognized as early as 1801 by Johann Ritter that the solar spectrum had an invisible component beyond the violet range Solar UV radiation is broadly subdivided into three regions UVA 320400 nm UVB 290320 nm and UVC 220290 nm ranked from long to shorter wavelengths from smaller to larger energies Most UVB and all UVC is absorbed by ozone O 3 molecules in the upper atmosphere Consequently 99 of the solar UV radiation reaching the Earths surface is UVA Human Exposure to UV Radiation It is largely exposure to UVB that causes skin cancer It is estimated that as many as 20 of adults will develop skin cancer over the course of their lifetime Again treatment is often successful if caught early Despite very little UVB reaching the Earths surface there are substantial increases in skincancer rates in countries such as Australia indicating how important it is that UVB and UVC continue to be absorbed by the upper atmosphere All UV radiation can damage collagen fibers resulting in an acceleration of the aging process of skin and the formation of wrinkles Because there is so little UVB and UVC reaching the Earths surface sunburn is caused by large exposures and skin cancer from repeated exposure Some studies indicate a link between overexposure to the Sun when young and melanoma later in life The tanning response is a defense mechanism in which the body produces pigments to absorb future exposures in inert skin layers above living cells Basically UVB radiation excites DNA molecules distorting the DNA helix leading to mutations and the possible formation of cancerous cells Repeated exposure to UVB may also lead to the formation of cataracts in the eyesa cause of blindness among people living in the equatorial belt where medical treatment is limited Cataracts clouding in the eyes lens and a loss of vision are age related 60 of those between the ages of 65 and 74 will develop cataracts However treatment is easy and successful as one replaces the lens of the eye with a plastic lens Prevention is important Eye protection from UV is more effective with plastic sunglasses than those made of glass A major acute effect of extreme UV exposure is the suppression of the immune system both locally and throughout the body Lowintensity ultraviolet is used to sterilize haircutting implements implying that the energy associated with ultraviolet is deposited in a manner different from lowerfrequency electromagnetic waves Actually this is true for all electromagnetic waves with frequencies greater than visible light Flash photography is generally not allowed of precious artworks and colored prints because the UV radiation from the flash can cause photodegradation in the artworks Often artworks will have an extrathick layer of glass in front of them which is especially designed to absorb UV radiation UV Light and the Ozone Layer If all of the Suns ultraviolet radiation reached the Earths surface there would be extremely grave effects on the biosphere from the severe cell damage it causes However the layer of ozone O 3 in our upper atmosphere 10 to 50 km above the Earth protects life by absorbing most of the dangerous UV radiation Unfortunately today we are observing a depletion in ozone concentrations in the upper atmosphere This depletion has led to the formation of an ozone hole in the upper atmosphere The hole is more centered over the southern hemisphere and changes with the seasons being largest in the spring This depletion is attributed to the breakdown of ozone molecules by refrigerant gases called chlorofluorocarbons CFCs The UV radiation helps dissociate the CFCs releasing highly reactive chlorine Cl atoms which catalyze the destruction of the ozone layer For example the reaction of CFCl 3 with a photon of light hv can be written as CFCl 3 h v CFCl 2 Cl Figure 9 This map of ozone concentration over Antarctica in October 2011 shows severe depletion suspected to be caused by CFCs Less dramatic but more general depletion has been observed over northern latitudes suggesting the effect is global With less ozone more ultraviolet radiation from the Sun reaches the surface causing more damage credit NASA Ozone Watch The Cl atom then catalyzes the breakdown of ozone as follows Cl O 3 ClO O 2 and ClO O 3 Cl 2O 2 A single chlorine atom could destroy ozone molecules for up to two years before being transported down to the surface The CFCs are relatively stable and will contribute to ozone depletion for years to come CFCs are found in refrigerants air conditioning systems foams and aerosols International concern over this problem led to the establishment of the Montreal Protocol agreement 1987 to phase out CFC production in most countries However developingcountry participation is needed if worldwide production and elimination of CFCs is to be achieved Probably the largest contributor to CFC emissions today is India But the protocol seems to be working as there are signs of an ozone recovery See Figure 9 Benefits of UV Light Besides the adverse effects of ultraviolet radiation there are also benefits of exposure in nature and uses in technology Vitamin D production in the skin epidermis results from exposure to UVB radiation generally from sunlight A number of studies indicate lack of vitamin D can result in the development of a range of cancers prostate breast colon so a certain amount of UV exposure is helpful Lack of vitamin D is also linked to osteoporosis Exposures with no sunscreen of 10 minutes a day to arms face and legs might be sufficient to provide the accepted dietary level However in UV radiation is used in the treatment of infantile jaundice and in some skin conditions It is also used in sterilizing workspaces and tools and killing germs in a wide range of applications It is also used as an analytical tool to identify substances When exposed to ultraviolet some substances such as minerals glow in characteristic visible wavelengths a process called fluorescence Socalled black lights emit ultraviolet to cause posters and clothing to fluoresce in the visible Ultraviolet is also used in special microscopes to detect details smaller than those observable with longerwavelength visiblelight microscopes Things Great and Small A Submicroscopic View of XRay Production Figure 10 Artists conception of an electron ionizing an atom followed by the recapture of an electron and emission of an Xray An energetic electron strikes an atom and knocks an electron out of one of the orbits closest to the nucleus Later the atom captures another electron and the energy released by its fall into a low orbit generates a highenergy EM wave called an Xray Xrays can be created in a highvoltage discharge They are emitted in the material struck by electrons in the discharge current There are two mechanisms by which the electrons create Xrays The first method is illustrated in Figure 10 An electron is accelerated in an evacuated tube by a high positive voltage The electron strikes a metal plate eg copper and produces Xrays Since this is a highvoltage discharge the electron gains sufficient energy to ionize the atom In the case shown an innershell electron one in an orbit relatively close to and tightly bound to the nucleus is ejected A short time later another electron is captured and falls into the orbit in a single great plunge The energy released by this fall is given to an EM wave known as an Xray Since the orbits of the atom are unique to the type of atom the energy of the Xray is characteristic of the atom hence the name characteristic Xray Figure 11 Artists conception of an electron being slowed by collisions in a material and emitting Xray radiation This energetic electron makes numerous collisions with electrons and atoms in a material it penetrates An accelerated charge radiates EM waves a second method by which Xrays are created The second method by which an energetic electron creates an Xray when it strikes a material is illustrated in Figure 11 The electron interacts with charges in the material as it penetrates These collisions transfer kinetic energy from the electron to the electrons and atoms in the material A loss of kinetic energy implies an acceleration in this case decreasing the electrons velocity Whenever a charge is accelerated it radiates EM waves Given the high energy of the electron these EM waves can have high energy We call them Xrays Since the process is random a broad spectrum of Xray energy is emitted that is more characteristic of the electron energy than the type of material the electron encounters Such EM radiation is called bremsstrahlung German for braking radiation XRays In the 1850s scientists such as Faraday began experimenting with highvoltage electrical discharges in tubes filled with rarefied gases It was later found that these discharges created an invisible penetrating form of very high frequency electromagnetic radiation This radiation was called an Xray because its identity and nature were unknown As described in Things Great and Small feature there are two methods by which Xrays are createdboth are submicroscopic processes and can be caused by highvoltage discharges While the lowfrequency end of the Xray range overlaps with the ultraviolet Xrays extend to much higher frequencies and energies Xrays have adverse effects on living cells similar to those of ultraviolet radiation and they have the additional liability of being more penetrating affecting more than the surface layers of cells Cancer and genetic defects can be induced by exposure to Xrays Because of their effect on rapidly dividing cells Xrays can also be used to treat and even cure cancer The widest use of Xrays is for imaging objects that are opaque to visible light such as the human body or aircraft parts In humans the risk of cell damage is weighed carefully against the benefit of the diagnostic information obtained However questions have risen in recent years as to accidental overexposure of some people during CT scansa mistake at least in part due to poor monitoring of radiation dose The ability of Xrays to penetrate matter depends on density and so an Xray image can reveal very detailed density information Figure 12 shows an example of the simplest type of Xray image an Xray shadow on film The amount of information in a simple Xray image is impressive but more sophisticated techniques such as CT scans can reveal threedimensional information with details smaller than a millimeter Figure 12 This shadow Xray image shows many interesting features such as artificial heart valves a pacemaker and the wires used to close the sternum credit P P Urone The use of Xray technology in medicine is called radiologyan established and relatively cheap tool in comparison to more sophisticated technologies Consequently Xrays are widely available and used extensively in medical diagnostics During World War I mobile Xray units advocated by Madame Marie Curie were used to diagnose soldiers Because they can have wavelengths less than 001 nm Xrays can be scattered a process called Xray diffraction to detect the shape of molecules and the structure of crystals Xray diffraction was crucial to Crick Watson and Wilkins in the determination of the shape of the doublehelix DNA molecule Xrays are also used as a precise tool for tracemetal analysis in Xray induced fluorescence in which the energy of the Xray emissions are related to the specific types of elements and amounts of materials present Gamma Rays Figure 13 This is an image of the γ rays emitted by nuclei in a compound that is concentrated in the bones and eliminated through the kidneys Bone cancer is evidenced by nonuniform concentration in similar structures For example some ribs are darker than others credit P P Urone Soon after nuclear radioactivity was first detected in 1896 it was found that at least three distinct types of radiation were being emitted The most penetrating nuclear radiation was called a gamma ray γ ray again a name given because its identity and character were unknown and it was later found to be an extremely high frequency electromagnetic wave In fact γ rays are any electromagnetic radiation emitted by a nucleus This can be from natural nuclear decay or induced nuclear processes in nuclear reactors and weapons The lower end of the γ ray frequency range overlaps the upper end of the Xray range but γ rays can have the highest frequency of any electromagnetic radiation Gamma rays have characteristics identical to Xrays of the same frequencythey differ only in source At higher frequencies γ rays are more penetrating and more damaging to living tissue They have many of the same uses as Xrays including cancer therapy Gamma radiation from radioactive materials is used in nuclear medicine Figure 13 shows a medical image based on γ rays Food spoilage can be greatly inhibited by exposing it to large doses of γ radiation thereby obliterating responsible microorganisms Damage to food cells through irradiation occurs as well and the longterm hazards of consuming radiationpreserved food are unknown and controversial for some groups Both Xray and γ ray technologies are also used in scanning luggage at airports Detecting Electromagnetic Waves from Space A final note on star gazing The entire electromagnetic spectrum is used by researchers for investigating stars space and time As noted earlier Penzias and Wilson detected microwaves to identify the background radiation originating from the Big Bang Radio telescopes such as the Arecibo Radio Telescope in Puerto Rico and Parkes Observatory in Australia were designed to detect radio waves Infrared telescopes need to have their detectors cooled by liquid nitrogen to be able to gather useful signals Since infrared radiation is predominantly from thermal agitation if the detectors were not cooled the vibrations of the molecules in the antenna would be stronger than the signal being collected The most famous of these infrared sensitive telescopes is the James Clerk Maxwell Telescope in Hawaii The earliest telescopes developed in the seventeenth century were optical telescopes collecting visible light Telescopes in the ultraviolet Xray and γ ray regions are placed outside the atmosphere on satellites orbiting the Earth The Hubble Space Telescope launched in 1990 gathers ultraviolet radiation as well as visible light In the Xray region there is the Chandra Xray Observatory launched in 1999 and in the γ ray region there is the new Fermi Gammaray Space Telescope launched in 2008taking the place of the Compton Gamma Ray Observatory 19912000 PhET Explorations Color Vision Make a whole rainbow by mixing red green and blue light Change the wavelength of a monochromatic beam or filter white light View the light as a solid beam or see the individual photons Click to run the simulation Section Summary The relationship among the speed of propagation wavelength and frequency for any wave is given by v W fλ so that for electromagnetic waves c fλ where f is the frequency λ is the wavelength and c is the speed of light The electromagnetic spectrum is separated into many categories and subcategories based on the frequency and wavelength source and uses of the electromagnetic waves Any electromagnetic wave produced by currents in wires is classified as a radio wave the lowest frequency electromagnetic waves Radio waves are divided into many types depending on their applications ranging up to microwaves at their highest frequencies Infrared radiation lies below visible light in frequency and is produced by thermal motion and the vibration and rotation of atoms and molecules Infrareds lower frequencies overlap with the highestfrequency microwaves Visible light is largely produced by electronic transitions in atoms and molecules and is defined as being detectable by the human eye Its colors vary with frequency from red at the lowest to violet at the highest Ultraviolet radiation starts with frequencies just above violet in the visible range and is produced primarily by electronic transitions in atoms and molecules Xrays are created in highvoltage discharges and by electron bombardment of metal targets Their lowest frequencies overlap the ultraviolet range but extend to much higher values overlapping at the high end with gamma rays Gamma rays are nuclear in origin and are defined to include the highestfrequency electromagnetic radiation of any type Conceptual Questions If you live in a region that has a particular TV station you can sometimes pick up some of its audio portion on your FM radio receiver Explain how this is possible Does it imply that TV audio is broadcast as FM Explain why people who have the lens of their eye removed because of cataracts are able to see lowfrequency ultraviolet How do fluorescent soap residues make clothing look brighter and whiter in outdoor light Would this be effective in candlelight Give an example of resonance in the reception of electromagnetic waves Illustrate that the size of details of an object that can be detected with electromagnetic waves is related to their wavelength by comparing details observable with two different types for example radar and visible light or infrared and Xrays Why dont buildings block radio waves as completely as they do visible light Make a list of some everyday objects and decide whether they are transparent or opaque to each of the types of electromagnetic waves Your friend says that more patterns and colors can be seen on the wings of birds if viewed in ultraviolet light Would you agree with your friend Explain your answer The rate at which information can be transmitted on an electromagnetic wave is proportional to the frequency of the wave Is this consistent with the fact that laser telephone transmission at visible frequencies carries far more conversations per optical fiber than conventional electronic transmission in a wire What is the implication for ELF radio communication with submarines Give an example of energy carried by an electromagnetic wave In an MRI scan a higher magnetic field requires higher frequency radio waves to resonate with the nuclear type whose density and location is being imaged What effect does going to a larger magnetic field have on the most efficient antenna to broadcast those radio waves Does it favor a smaller or larger antenna Laser vision correction often uses an excimer laser that produces 193nm electromagnetic radiation This wavelength is extremely strongly absorbed by the cornea and ablates it in a manner that reshapes the cornea to correct vision defects Explain how the strong absorption helps concentrate the energy in a thin layer and thus give greater accuracy in shaping the cornea Also explain how this strong absorption limits damage to the lens and retina of the eye Problems Exercises a Two microwave frequencies are authorized for use in microwave ovens 900 and 2560 MHz Calculate the wavelength of each b Which frequency would produce smaller hot spots in foods due to interference effects a Calculate the range of wavelengths for AM radio given its frequency range is 540 to 1600 kHz b Do the same for the FM frequency range of 880 to 108 MHz A radio station utilizes frequencies between commercial AM and FM What is the frequency of a 1112mwavelength channel Find the frequency range of visible light given that it encompasses wavelengths from 380 to 760 nm Combing your hair leads to excess electrons on the comb How fast would you have to move the comb up and down to produce red light Electromagnetic radiation having a 150 μ m wavelength is classified as infrared radiation What is its frequency Approximately what is the smallest detail observable with a microscope that uses ultraviolet light of frequency 120 10 15 Hz A radar used to detect the presence of aircraft receives a pulse that has reflected off an object 6 10 5 s after it was transmitted What is the distance from the radar station to the reflecting object Some radar systems detect the size and shape of objects such as aircraft and geological terrain Approximately what is the smallest observable detail utilizing 500MHz radar Determine the amount of time it takes for Xrays of frequency 3 10 18 Hz to travel a 1 mm and b 1 cm If you wish to detect details of the size of atoms about 1 10 10 m with electromagnetic radiation it must have a wavelength of about this size a What is its frequency b What type of electromagnetic radiation might this be If the Sun suddenly turned off we would not know it until its light stopped coming How long would that be given that the Sun is 150 10 11 m away Distances in space are often quoted in units of light years the distance light travels in one year a How many meters is a light year b How many meters is it to Andromeda the nearest large galaxy given that it is 200 10 6 light years away c The most distant galaxy yet discovered is 120 10 9 light years away How far is this in meters A certain 500Hz AC power line radiates an electromagnetic wave having a maximum electric field strength of 130 kVm a What is the wavelength of this very low frequency electromagnetic wave b What is its maximum magnetic field strength During normal beating the heart creates a maximum 400mV potential across 0300 m of a persons chest creating a 100Hz electromagnetic wave a What is the maximum electric field strength created b What is the corresponding maximum magnetic field strength in the electromagnetic wave c What is the wavelength of the electromagnetic wave a The ideal size most efficient for a broadcast antenna with one end on the ground is onefourth the wavelength λ 4 of the electromagnetic radiation being sent out If a new radio station has such an antenna that is 500 m high what frequency does it broadcast most efficiently Is this in the AM or FM band b Discuss the analogy of the fundamental resonant mode of an air column closed at one end to the resonance of currents on an antenna that is onefourth their wavelength a What is the wavelength of 100MHz radio waves used in an MRI unit b If the frequencies are swept over a100 range centered on 100 MHz what is the range of wavelengths broadcast a What is the frequency of the 193nm ultraviolet radiation used in laser eye surgery b Assuming the accuracy with which this EM radiation can ablate the cornea is directly proportional to wavelength how much more accurate can this UV be than the shortest visible wavelength of light TVreception antennas for VHF are constructed with cross wires supported at their centers as shown in link The ideal length for the cross wires is onehalf the wavelength to be received with the more expensive antennas having one for each channel Suppose you measure the lengths of the wires for particular channels and find them to be 194 and 0753 m long respectively What are the frequencies for these channels Figure 14 A television reception antenna has cross wires of various lengths to most efficiently receive different wavelengths Conversations with astronauts on lunar walks had an echo that was used to estimate the distance to the Moon The sound spoken by the person on Earth was transformed into a radio signal sent to the Moon and transformed back into sound on a speaker inside the astronauts space suit This sound was picked up by the microphone in the space suit intended for the astronauts voice and sent back to Earth as a radio echo of sorts If the roundtrip time was 260 s what was the approximate distance to the Moon neglecting any delays in the electronics Lunar astronauts placed a reflector on the Moons surface off which a laser beam is periodically reflected The distance to the Moon is calculated from the roundtrip time a To what accuracy in meters can the distance to the Moon be determined if this time can be measured to 0100 ns b What percent accuracy is this given the average distance to the Moon is 384 10 8 m Radar is used to determine distances to various objects by measuring the roundtrip time for an echo from the object a How far away is the planet Venus if the echo time is 1000 s b What is the echo time for a car 750 m from a Highway Police radar unit c How accurately in nanoseconds must you be able to measure the echo time to an airplane 120 km away to determine its distance within 100 m Integrated Concepts a Calculate the ratio of the highest to lowest frequencies of electromagnetic waves the eye can see given the wavelength range of visible light is from 380 to 760 nm b Compare this with the ratio of highest to lowest frequencies the ear can hear Integrated Concepts a Calculate the rate in watts at which heat transfer through radiation occurs almost entirely in the infrared from 10 m 2 of the Earths surface at night Assume the emissivity is 090 the temperature of the Earth is 15ºC and that of outer space is 27 K b Compare the intensity of this radiation with that coming to the Earth from the Sun during the day which averages about 800 Wm 2 only half of which is absorbed c What is the maximum magnetic field strength in the outgoing radiation assuming it is a continuous wave Glossary electromagnetic spectrum the full range of wavelengths or frequencies of electromagnetic radiation radio waves electromagnetic waves with wavelengths in the range from 1 mm to 100 km they are produced by currents in wires and circuits and by astronomical phenomena microwaves electromagnetic waves with wavelengths in the range from 1 mm to 1 m they can be produced by currents in macroscopic circuits and devices thermal agitation the thermal motion of atoms and molecules in any object at a temperature above absolute zero which causes them to emit and absorb radiation radar a common application of microwaves Radar can determine the distance to objects as diverse as clouds and aircraft as well as determine the speed of a car or the intensity of a rainstorm infrared radiation IR a region of the electromagnetic spectrum with a frequency range that extends from just below the red region of the visible light spectrum up to the microwave region or from 074μm to 300μm ultraviolet radiation UV electromagnetic radiation in the range extending upward in frequency from violet light and overlapping with the lowest Xray frequencies with wavelengths from 400 nm down to about 10 nm visible light the narrow segment of the electromagnetic spectrum to which the normal human eye responds amplitude modulation AM a method for placing information on electromagnetic waves by modulating the amplitude of a carrier wave with an audio signal resulting in a wave with constant frequency but varying amplitude extremely low frequency ELF electromagnetic radiation with wavelengths usually in the range of 0 to 300 Hz but also about 1kHz carrier wave an electromagnetic wave that carries a signal by modulation of its amplitude or frequency frequency modulation FM a method of placing information on electromagnetic waves by modulating the frequency of a carrier wave with an audio signal producing a wave of constant amplitude but varying frequency TV video and audio signals broadcast on electromagnetic waves very high frequency VHF TV channels utilizing frequencies in the two ranges of 54 to 88 MHz and 174 to 222 MHz ultrahigh frequency UHF TV channels in an even higher frequency range than VHF of 470 to 1000 MHz Xray invisible penetrating form of very high frequency electromagnetic radiation overlapping both the ultraviolet range and the γ ray range gamma ray γ ray extremely high frequency electromagnetic radiation emitted by the nucleus of an atom either from natural nuclear decay or induced nuclear processes in nuclear reactors and weapons The lower end of the γ ray frequency range overlaps the upper end of the Xray range but γ rays can have the highest frequency of any electromagnetic radiation Selected Solutions to Problems Exercises 1 a 333 cm 900 MHz 117 cm 2560 MHz b The microwave oven with the smaller wavelength would produce smaller hot spots in foods corresponding to the one with the frequency 2560 MHz 3 2696 MHz 5 50 10 14 Hz 7 λ c f 3 00 10 8 ms 1 20 10 15 Hz 2 50 10 7 m 9 0600 m 11 a f c λ 3 00 10 8 ms 1 10 10 m 3 10 18 Hz b Xrays 14 a 600 10 6 m b 433 10 5 T 16 a 150 10 6 Hz AM band b The resonance of currents on an antenna that is 14 their wavelength is analogous to the fundamental resonant mode of an air column closed at one end since the tube also has a length equal to 14 the wavelength of the fundamental oscillation 18 a 155 10 15 Hz b The shortest wavelength of visible light is 380 nm so that λ visible λ UV 380 nm 193 nm 197 197 In other words the UV radiation is 97 more accurate than the shortest wavelength of visible light or almost twice as accurate 20 390 10 8 m 22 a 150 10 11 m b 0500 μs c 667 ns 24 a 35 10 2 Wm 2 b 88 c 17 μT

B I B I I O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 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O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 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DIY Ear Warmer Headband January 10 2013 by Amber 24 Comments For Christmas my husband got me one of those ear warmer headband things that I can wear in the winter when I am running to keep my ears warm That is of course if the temperature would raise above like 10 degrees so I could actually go outside and run I took one look at it and realized thats about the easiest sewing project a person could make You could make 50 of them Every person you know could wear one these things are so easy Ear Warmer Headband Tutorial Supplies Needed Fleecevery small amount probably 18 of a yard or less BUT you need to make sure that you can cut your strips the stretchy direction see below so test which direction is stretchy before you buy it You need to buy enough fleece that you can cut your strips the stretchy direction CRAZY LITTLE PROJECTS TV Matching thread First measure your head to see how big it is Incidentally when measuring heads we discovered that my 4 year olds head is almost as big as mine Hes got quite the noggin Now grab your fleece You are going to notice that if you pull it one direction it is stretchy the other way not so much You need to cut 2 strips that are 4 wide by the measurement of your head so mine was 225 but make sure that the long measurement is cut so that your strips are stretchy Now put the strips one of top of the other if your fleece has a right side make sure the right sides are together on the inside Sew down each of the long sides leaving the short ends open Turn right side out and top stitch along each of the long edges Then grab both of the ends and zigzag them together And thats it Youve got a headband If it is too large no problem just zigzag in a little farther Filed Under Quick Easy Crafts Sewing Patterns Valentine Throw Pillows Penguin Hooded Towel Tutorial MAKE Life Happy Subscribe now for free sewing patterns fun craft ideas yummy dessert recipes emailed right to your inbox and its all FREE Marketing by

O B I I O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O

crazy little projects
ear warmer headband


What Sewing Supplies to Buy for Beginning Sewing August 3 2017 by Amber 59 Comments Whats the Project So youre ready to get started learning to sew but you dont know what sewing supplies notions and equipment you need in order to get going This list will help Youve got that machine and you are ready to get started sewing You know youre going to need some sewing supplies in order to get going but what do you need There are SO many gadgets and notionsbobbins and seam rippers measuring tapes and chalk pencils scissors pins and so much more And thats not to mention all of the fabric So how do you know what to get It can be intimidating when you dont know what you are doing as you get started sewing but it doesnt have to be hard There are a handful of sewing supplies that you will want to have on hand before you get started Then you can build up other accessories as you go CRAZY LITTLE PROJECTS TV Before you get too stressed out let me walk you through the supplies you want to grab before you get started Sewing Supplies Needed for Beginning Sewing This contains affiliate links Scissors A great pair of scissors is a must have when sewing These will need to be fabric only scissors meaning you dont use them for anything else This will keep them sharp and will be perfect for cutting your fabric These are the sewing scissors I recommend Theyre pink hello perfection and they cut great Pins Another very basic supply that you will need are some pins Actually lots of pins I really like them to have large heads on them so that they are easy to grab like these ones And you will want a pin cushion of some sort to keep them on I love a magnetic one because its easy to grab them and put them back without too much effort Seam Ripper As much as you dont want to youre going to be using a seam ripper when you sew and probably frequently Ive been sewing for years and years and still use mine on just about every project that I sew I love this one because its large enough for your hands to comfortably hold and the top is designed to help you grab the little threads and get them out of there Bobbins Bobbins are the part of your thread that comes up from the bottom You will always need one in your machine but the truth is its a pain to wind new bobbin every time so you will want a pack of bobbins so that you can keep them in all the colors of your thread and not have to wind new ones with each project Every machine uses a different typesome metal and some plastic So double check your users manual before you order But these are my favorites Thread And speaking of thread youre going to need some You will always want thread in the color of what you are sewing so it can be a little bit tricky to get all the colors you will eventually want Start with white and black for sure and maybe get a handful of other colors to get you going Then as you buy fabric for new projects make sure that you grab matching thread I recommend Coats and Clark thread if you can get it Measuring Tape It will be very handy to have a measuring tape on hand when you sew so you might as well grab one now Its a cheap addition to your sewing supplies stash and will come in handy all the time Heres the one I love to use Fabric The fun part Obviously you are going to need fabric in order to get started sewing right But where to even begin Dont worry over time you will build up your fabric stashprobably so that you have more fabric than you can possibly use Because buying fabric is fun If you need help on how to buy fabric I cover that in this tutorial here Sewing Machine Needles You might want to keep a few extra sewing machine needles handy because they WILL break occasionally and its a pain if you have to run out to the store to get new ones all the time Check which kind your machine needs but these are likely to work Other Sewing Supplies Those are the basics that Ive already covered Those are things that you really need to get in order to get started sewing Theres a handful of other things you might want to have on hand These are less crucial from the getgo but if youre looking to stock up grab some of these things Elastic Zippers Bias Tape Chalk pencils Rotary Cutter and Cutting Mat Velcro Hopefully this list of sewing supplies helps you get going on your journey to learn to sew You Might Also Like Getting Started Sewing Everything You Need to Learn to Sew How to Buy Fabric Pin It Filed Under Learn to Sew Learn to Sew Lessons Sew Something Sewing Classes Sewing Favorites Sewing Tips Books That Keep You on the Edge of Your Seat Best Summer Reads for Women MAKE Life Happy Subscribe now for free sewing patterns fun craft ideas yummy dessert recipes emailed right to your inbox and its all FREE Marketing by

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Prev FOLLOW CRÈME DE LA CRÈME about the event HAUTE COUTURE SHOW THE LOCATION WHO WILL BE HERE REGISTRATION DETAILS SUNDAY NOVEMBER 18 2018 FAIRMONT HOTEL VANCOUVER 900 West Georgia Street Vancouver BC V6C 2W6 1100AM to 530PM WEDDING SHOWCASE 100PM HAUTE COUTURE FASHION SHOW 330PM ENCORE PRESENTATION TICKETS 60 PER PERSON AT THE DOOR includes fashion show scrumptious tastings fullscale pampering gift bag which will be filled with goodies by the time you leave the showcase Romance enchantment and unbelievable elegance embodies this years soiree One Day A culmination of all your dreams and expectations When the crème de la crème of Vancouver assemble to present infinite possibilities 0150 Player error The player is having trouble Well have it back up and running as soon as possible CRÈME DE LA CRÈME CRÈME DE LA CRÈME raises the standard of wedding shows with an unmatched haute couture fashion show trendsetting designs and showcase of products and services that convey style artistry and excellence 2018 EXHIBITORS See the full list of all those participating in this years Grand Wedding Showcase

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