A2 Daily A Level Physics question
In a vacuum photoelectric experiment, a clean metal surface is illuminated by monochromatic light of fixed frequency well above the threshold. The anode is held sufficiently positive to collect all emitted electrons. If the light intensity is doubled while the frequency is unchanged, which statement must be true?
Answer
The correct answer is C.
Correct: C — The saturation photoelectric current doubles because twice as many photons per second arrive. A is wrong: the maximum kinetic energy depends on photon frequency minus the work function, so with frequency unchanged it does not increase. B is wrong: the stopping potential is set by the maximum kinetic energy, which is unchanged if the frequency is the same. C is correct: doubling intensity at fixed frequency doubles the photon arrival rate, so with all electrons collected the current increases by a factor of 2. D is wrong: the work function is a material property and does not change with light intensity.