User: The greenhouse effect is a result of A. absorption and radiation of energy in the hydrosphere. B. consumption of fruits and vegetables that produce a biofuel. C. absorption and radiation of energy in the atmosphere.
A principal focus or focal point is a special focus: 1  For a lens, or a spherical or parabolic mirror, it is a point onto which collimated light parallel to the axis is focused. Since light can pass through a lens in either direction, a lens has two focal pointsâone on each side.
focus noun (POSITION) âº earth science [ C/U ] A focus is also the exact position inside the earth where an earthquake begins. âº A photograph or an image seen through a device with a lens, such as a microscope, telescope, or camera, that is in focus is clear and one that is out of focus is not clear.