Two metals have different work functions under the same beam. How much do their maximum kinetic energies differ?

By exactly the difference in work functions, because the photon energy is the same and Kmax = hf minus W changes only with W.

Why does the photocurrent stop rising once it saturates?

The number of electrons available per second is fixed by the photon rate and the quantum efficiency; extra voltage only collects them all.

Photoelectric Effect Practice Paper 4: mixed calculations and comparisons

2026-11-03

S · 6

This paper mixes the whole chapter: photon energy and threshold, maximum kinetic energy and stopping voltage, photon streams and current, a comparison of two metals, and the Planck constant from a graph. Keep the units explicit and never mix eV with joules. Every value is checked by computer.

Quick answer　From 6.0e14 Hz the photon carries 2.49 eV; threshold 7.24e14 Hz; 550 nm gives 2.26 eV; stopping voltage 2.0 V; 200 nm against 4.5 eV leaves 1.72 eV; 2.0e14 electrons per second; 2.51e15 photons per second; a difference of 0.50 eV; h = 6.4e-34 with 2.2 eV; energy depends on frequency.

01　Paper details (check answers afterwards)

Item	Detail
Questions	10 questions
Suggested time	25 minutes
Difficulty mix	Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1
Chapter	Chapter: Photoelectric Effect
Level	S6

02　Questions (10 items)

FoundationWhat is the energy in eV of a photon of frequency 6.0e14 Hz?
FoundationWhat is the threshold frequency of a metal with work function 3.0 eV?
FoundationWhat is the energy in eV of a photon of wavelength 550 nm?
FoundationThe maximum kinetic energy of the photoelectrons is 2.0 eV. What is the stopping voltage?
IntermediateLight of 200 nm falls on a metal of work function 4.5 eV. What is the maximum kinetic energy?
IntermediateThe saturation photocurrent is 32 microamperes. How many photoelectrons reach the anode each second?
IntermediateA 1.0 mW beam of 500 nm light. How many photons leave it each second?
ChallengeThe same 350 nm beam strikes two metals with work functions 2.0 eV and 2.5 eV. How much do the maximum kinetic energies differ?
ChallengeThe stopping voltage is 0.20 V at 6.0e14 Hz and 1.00 V at 8.0e14 Hz. Find h and the work function.
Error redoA student says photon energy depends on intensity. Where is the error?

03　Answers and one-line notes

#	Answer	One-line note
1	2.49 eV.	6.63e-34 times 6.0e14 = 3.98e-19 J, divided by 1.60e-19.
2	7.24e14 Hz.	f0 = W over h = 4.80e-19 divided by 6.63e-34.
3	2.26 eV, that is 3.62e-19 J.	E = hc over lambda = 1.989e-25 divided by 5.50e-7 = 3.616e-19 J.
4	2.0 V.	The stopping voltage in volts equals the maximum kinetic energy in eV.
5	About 1.72 eV.	The photon carries 9.95e-19 J, that is 6.22 eV; subtract 4.5 eV.
6	2.0e14 electrons.	Electrons per second = I over e = 32e-6 divided by 1.60e-19.
7	About 2.51e15 photons.	Each photon carries 3.98e-19 J, so 1.0e-3 divided by 3.98e-19.
8	They differ by 0.50 eV, with values 1.55 eV and 1.05 eV.	The photon carries 3.55 eV; subtracting each work function gives the two values, whose difference is the difference in work functions.
9	h = 6.4e-34 J s and the work function is 2.2 eV.	Gradient = e times delta V over delta f = 1.60e-19 times 0.80 divided by 2.0e14; then hf minus eVs gives W = 3.52e-19 J.
10	Photon energy is fixed by frequency alone, E = hf; intensity sets only the number of photons per second.	This error comes from carrying the wave idea that energy depends on amplitude over to photons.

04　What to do after marking

After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
Repeat the same item two days later; move to the next paper only when both attempts are correct.
Parents only need the answer and note columns; there is no need to explain every item.

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Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.