Q. An image of the sun is formed by a lens, of the focal length of 30cm, on the metal surface of a photoelectric cell and a photoelectric current I is produced. The lens forming the image is then replaced by another of the same diameter but of focal length 15cm. The photoelectric current in this case is
Sol: As diameter of lens is same , hence it will collect equal amount of light . So , Intensity of light remains same . The photoelectric current will also be same .