JEE Main 2025 · 4 April · morning · Single correct · +4 / −1
Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R
Assertion A : In photoelectric effect, on increasing the intensity of incident light the stopping potential increases.
Reason R : Increase in intensity of light increases the rate of photoelectrons emitted, provided the frequency of incident light is greater than threshold frequency.
In the light of the above statements, choose the correct answer from the options given below
- (a) Both A and R are true and R is the correct explanation of A
- (b) A is false but R is true
- (c) Both A and R are true but R is NOT the correct explanation of A
- (d) A is true but R is false
Answer and solution
Answer (b) A is false but R is true
Solution
Physics sir · 4 steps
Stopping potential depends on each photon's energy, not on how many photons arrive.
- What sets stopping potential. The stopping potential V₀ must stop the fastest electron, so eV₀ equals the maximum kinetic energy. That energy comes from a single photon.
eV₀ = Kₘₐₓ = hν - φ
- Check Assertion A. The right side depends only on the frequency ν and the work function φ. Raising the intensity at the same frequency leaves each photon's energy hν unchanged, so V₀ stays the same. A is false.
- Check Reason R. Higher intensity means more photons strike the surface each second. When ν is above the threshold frequency, each absorbed photon can free one electron, so more photoelectrons come out per second and the photocurrent rises. R is true.
- So. A is false and R is true, which is option (b).
The idea to keep. Intensity controls how many electrons come out (the current). Frequency controls how fast they come out (the stopping potential). Keep these two effects separate.
Answer from the NTA final answer key. Solution by PrepWiser.