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MODEL PAPER 5 — Physics STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsMODEL PAPER 51 Mark
MCQ
Assertion (A): When ultraviolet light is incident on a photocell, its stopping potential is $V _0$ and the maximum kinetic energy of the photoelectrons is $K _{\max }$. When the ultraviolet light is replaced by X-rays, both $V _0$ and $K _{\max }$. increase.
Reason (R): Photoelectrons are emitted with speeds ranging from zero to a maximum value because of the range of frequencies present in the incident light.
  • A
    Both A and R are true and R is the correct explanation of A.
  • B
    Both A and R are true but R is not the correct explanation of A.
  • C
    A is true but R is false.
  • D
    A is false but R is true.
✓

Answer

(c) A is true but R is false.
Explanation: We know that
$eV _0= K _{\max }= hv -\phi$
where $\phi$ is the work function.
Hence, as v increases (note that the frequency of X -rays is greater than that of $U . V$. rays), both $V _0$ and $K _{\text {max }}$ increase. So, $A$ is true but $R$ is false.

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