DP Physics (first assessment 2025)

Question EXE.2.HL.TZ0.18b

Date	Example questions Example questions	Marks available	[Maximum mark: 4]	Reference code	EXE.2.HL.TZ0.18b
Level	HL	Paper	2	Time zone	TZ0
Command term	Estimate	Question number	b	Adapted from	N/A

[Maximum mark: 4]

EXE.2.HL.TZ0.18b

The beam is produced by accelerating electrons through an electric potential difference U.

(b)

A typical interatomic distance in the graphite crystal is of the order of $2 \times 10^{- 10}$ m. Estimate the minimum value of U for the pattern in (a) to be formed on the screen.

[4]

Markscheme

The de Broglie wavelength of the electrons should be comparable to or shorter than the interatomic distance / $2 \times 10^{- 10}$ m ✓

Momentum of electrons $\approx \frac{6.63 \times 10^{- 34}}{2 \times 10^{- 10}}$ « $= 3.32 \times 10^{- 2}$ N s» ✓

Kinetic energy of electrons = « $\frac{p^{2}}{2 m} = \frac{{(3.32 \times 10^{- 24})}^{2}}{2 \times 9.11 \times 10^{- 31}} =$ » $6.0 \times 10^{- 18}$ «J» ✓

U = « $\frac{E}{e} = \frac{6.10 \times 10^{- 18}}{1.6 \times 10^{- 19}} =$ »40 «V» ✓

Syllabus sections

E. Nuclear and quantum physics

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

Question EXE.2.HL.TZ0.18b

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