An image of the sun is formed by a lens of focal length 30 cm on the metal surface of a photoelectric cell and it produces a current I. The lens forming the image is then replaced by another lens of the same diameter but of focal length 15 cm. The photoelectric current in this case will be: (In both cases the plate is kept at the focal plane and normal to the axis lens)
Correct answer: C. I
- A. I/2
- B. 2I
- C. I
- D. 4I
Explanation
Lenses of the same diameter collect equal amount of light. Intensity is the measure of amount of light colleted, hence the intnensity remains the same. Intensity is measured by the photoelectric current which would also remain the same. Photoelectric current = (I)
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Classical physics cannot explain blackbody radiation and related observations, leading to Planck’s quantum theory, in which energy is emitted or absorbed in discrete packets. Photons provide the particle model of light, with energy and momentum linked to frequency and wavelength, including the photoelectric effect and its threshold frequency.
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