DP Physics (first assessment 2025)

Question EXE.2.HL.TZ0.20

Date	Example questions Example questions	Marks available	[Maximum mark: 8]	Reference code	EXE.2.HL.TZ0.20
Level	HL	Paper	2	Time zone	TZ0
Command term	Deduce, Determine, Outline, Show that, State	Question number	20	Adapted from	N/A

20.

[Maximum mark: 8]

EXE.2.HL.TZ0.20

(a)

The quantity $\frac{h}{m_{e} c}$ is known as the Compton wavelength.

Show that the Compton wavelength is about 2.4 pm.

[1]

Markscheme

2.43 pm ✓

(b)

A photon with a wavelength of 6.00 pm interacts with a stationary electron. After the interaction the photon's wavelength has changed by 2.43 pm.

(b.i)

State the wavelength of the photon after the interaction.

[1]

Markscheme

8.43 pm ✓

(b.ii)

Outline why the wavelength of the photon has changed.

[2]

Markscheme

(Energy of photon inversely prop to wavelength)

photon transfers some of its energy to the electron. ✓

If its energy decreases so its wavelength increases. ✓

(b.iii)

Deduce the scattering angle for the photon.

[2]

Markscheme

(for this interaction)

$Δ λ = \frac{h}{m_{e} c} (1 - \cos θ) = \frac{h}{m_{e} c}$ and therefore $(1 - \cos θ)$ must equal 1 ✓

so cos theta = 0 and theta = 90 deg ✓

(b.iv)

Determine, in J, the kinetic energy of the electron after the interaction.

[2]

Markscheme

(Because energy is conserved)

$E_{k} = h c (\frac{1}{λ_{i}} - \frac{1}{λ_{f}})$

$= 6.63 \times 10^{- 34} \times 3.00 \times 10^{8} (\frac{1}{6.00 \times 10^{- 12}} - \frac{1}{8.43 \times 10^{- 12}})$ ✓

9.6 fJ ✓

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