The assumption that black-body radiation is thermal leads to an accurate prediction: the total amount of emitted energy goes up with the temperature according to a definite rule, the Stefan–Boltzmann law (1879–84). But it was also known that the colour of the light given off by a hot object changes with the temperature, so that "white hot" is hotter than "red hot". Nevertheless, Wilhelm Wien discovered the mathematical relationship between the peaks of the curves at different temperatures, by using the principle of adiabatic invariance. At each different temperature, the curve is moved over by Wien's displacement law (1893). Wien also proposed an approximation for the spectrum of the object, which was correct at high frequencies (short wavelength) but not at low frequencies (long wavelength). It still was not clear why the spectrum of a hot object had the form that it has (see diagram). COUNT 14
QSN1 What do scientists assume black body radiation is? ANS1 thermal QSN2 What kind of prediction does the assumption that black body radiation is thermal lead to? ANS2 accurate QSN3 What type of changes in the light a hot object emits as the object's temperature changes? ANS3 colour QSN4 What law describes the changes in light emitted by a hot object? ANS4 Stefan–Boltzmann law QSN5 What assumption that black-body radiation is what leads to an accurate prediction? ANS5 thermal QSN6 What does the Stefan-Boltzmann law state? ANS6 the total amount of emitted energy goes up with the temperature according to a definite rule QSN7 What about a hot object changes with the temperature? ANS7 the colour of the light QSN8 What color is hotter than "red hot"? ANS8 white hot QSN9 What did Wilhelm Wien discover? ANS9 the mathematical relationship between the peaks of the curves at different temperatures QSN10 What rule predicts that emitted energy increases with temperature? ANS10 the Stefan–Boltzmann law QSN11 What characteristic of the light emitted by a hot object changes with temperature? ANS11 the colour of the light given off QSN12 Who discovered the mathematical relationship between peaks and curves of light at different temperatures? ANS12 Wilhelm Wien QSN13 The rule that adjust the curve at different temperatures is known as what? ANS13 Wien's displacement law QSN14 Wien's spectrum model could not predict accurate at what end of the spectrum? ANS14 at low frequencies (long wavelength)