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Physics · 2025 · 3 marks
Dual Nature of Radiation and MatterEinstein’s Photoelectric Equation: Energy Quantum of Radiation3 marksUnderstandshort answer
CBSE 2025 · Region 1 · Set 1 · Q26
Answer the following giving reason: (a) All the photo electrons do not eject with the same kinetic energy when monochromatic light is incident on a…
Answer the following giving reason:
(a)
All the photo electrons do not eject with the same kinetic energy when monochromatic light is incident on a metal surface.
(b)
The saturation current in case (a) is different for different intensity.
(c)
If one goes on increasing the wavelength of light incident on a metal surface, keeping its intensity constant, emission of photo electrons stop at a certain wavelength for this metal.
Marking-scheme solution
Reason for
a) All photoelectrons not having same Kinetic Energy. $\displaystyle 1$
b) Having different saturation current for different intensity. $\displaystyle 1$
c) Stopping of emission of photoelectrons at a certain wavelength. $\displaystyle 1$
(a)
When monochromatic light is incident on a metal surface then more/less tightly bound electrons will emerge with less/more kinetic energy. So all the photoelectrons do not eject with same kinetic energy.
(b)
Maximum number of photoelectrons ejected per second (saturation current) is directly proportional to the Intensity of incident radiation Hence saturation current is different for different intensities.
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CBSE Class 12 Physics past-paper question from the 2025 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.