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.
a. the focal point of a lens. b. the focal length of a lens. c. the clear and sharply defined condition of an image. d. the position of a viewed object or the adjustment of an optical device necessary to produce a clear image: out of focus.