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.
The term âfocal pointâ in photography also applies to optics, where it represents a point in space where rays of light converge after they have been affected by an optical system. In the case of photographic lenses, this is a point behind the lens (inside the camera).