DP Physics (first assessment 2025)

Question 21M.2.HL.TZ1.10

Date	May 2021	Marks available	[Maximum mark: 7]	Reference code	21M.2.HL.TZ1.10
Level	HL	Paper	2	Time zone	TZ1
Command term	Calculate, Describe, Show that	Question number	10	Adapted from	N/A

10.

[Maximum mark: 7]

21M.2.HL.TZ1.10

In an electric circuit used to investigate the photoelectric effect, the voltage is varied until the reading in the ammeter is zero. The stopping voltage that produces this reading is 1.40 V.

(a)

Describe the photoelectric effect.

[2]

Markscheme

electrons are ejected from the surface of a metal ✓

after gaining energy from photons/electromagnetic radiation ✓

there is a minimum «threshold» energy/frequency
OR
maximum «threshold» wavelength ✓

(b)

Show that the maximum velocity of the photoelectrons is $700 {km s}^{- 1}$ .

[2]

Markscheme

« $e V = \frac{1}{2} m v^{2}$ » and manipulation to get $v$ ✓

$v = \sqrt{\frac{2 \times 1.6 \times 10^{- 19} \times 1.4}{9.1 \times 10^{- 31}}}$ OR $702 « {km s}^{- 1} »$ ✓

Must see either complete substitution or calculation to at least 3 s.f. for MP2

(c)

The photoelectrons are emitted from a sodium surface. Sodium has a work function of 2.3 eV.

Calculate the wavelength of the radiation incident on the sodium. State an appropriate unit for your answer.

[3]

Markscheme

$E = 2.3 + 1.4$ ✓

$λ = \frac{6.63 \times 10^{- 34} \times 3 \times 10^{8}}{3.7 \times 1.6 \times 10^{- 19}}$ ✓

$= 3.4 \times 10^{- 7} m OR 340 nm$ ✓

Must see an appropriate unit to award MP3.

Syllabus sections

E. Nuclear and quantum physics » E.2 Quantum physics

B. The particulate nature of matter » B.5 Current and circuits

Question 21M.2.HL.TZ1.10

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