Quantum physics: A Level Physics questions with answers
Free Quantum physics questions for A Level Physics (9702), part of Thermal & modern physics. Each question has the answer and the marking points an examiner would look for.
Electron diffraction provides evidence for the wave nature of particles.
(a)
Calculate the de Broglie wavelength of an electron accelerated through 2000 V.
[3]
(b)
Explain how the diffraction pattern changes if the accelerating voltage increases.
[2]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
2.7 × 10−11 m
eV = p2/2m C1 p = 2.41 × 10−23 N s C1 λ = h/p = 2.7 × 10−11 m A1
3
(b)
rings smaller
momentum increases so wavelength decreases B1 rings become smaller (less diffraction) B1
2
Question 2Structured · 8 marksA* challenge
The lowest four energy levels of hydrogen are −13.6 eV, −3.40 eV, −1.51 eV and −0.85 eV.
(a)
Explain how line emission spectra provide evidence for discrete electron energy levels.
[2]
(b)
State the number of different photon energies that can be emitted from these four levels.
[1]
(c)
Calculate the wavelength of the photon emitted when an electron moves from the third level to the second level.
[3]
(d)
State the region of the electromagnetic spectrum of this photon.
[1]
(e)
State one piece of evidence that electrons behave as waves.
[1]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
specific photon energies
each line is a specific frequency, so photons have specific energies B1 electrons can only lose energy in discrete amounts between levels B1
2
(b)
6
6 B1
1
(c)
6.58 × 10−7 m
ΔE = 1.89 eV = 3.02 × 10−19 J C1 λ = hc/ΔE C1 = 6.58 × 10−7 m A1
3
(d)
visible
visible light B1
1
(e)
electron diffraction
electron diffraction (e.g. through graphite) B1
1
Question 3Structured · 9 marks
Fig. 3.1 shows some of the energy levels of a hydrogen atom. The arrow shows one electron transition.
Fig. 3.1
(a)
Explain why the energy levels are given negative values.
[2]
(b)
Calculate the wavelength of the photon emitted in the transition shown in Fig. 3.1.
[3]
(c)
State the region of the electromagnetic spectrum of this photon.
[1]
(d)
Explain how the line spectrum of hydrogen provides evidence for discrete energy levels.
[2]
(e)
Calculate the ionisation energy of hydrogen in joules.
[1]
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Part
Answer and marking points
Marks
(a)
zero energy = electron free (at infinity); bound electron has less energy
the energy of a free electron (at infinity) is defined as zero B1 bound electrons have less energy so their energies are negative B1
2
(b)
4.88 × 10−7 m
ΔE = 2.55 eV = 4.08 × 10−19 J C1 λ = hc/ΔE C1 4.88 × 10−7 m A1
3
(c)
visible
visible B1
1
(d)
only specific wavelengths emitted; each corresponds to a transition between fixed levels
only certain wavelengths (lines) are emitted B1 each photon energy equals the difference between two fixed energy levels, so energy levels are discrete B1
2
(e)
2.18 × 10−18 J
13.6 × 1.60 × 10−19 = 2.18 × 10−18 J B1
1
Question 4Structured · 3 marks
Electromagnetic radiation of wavelength 336 nm is incident on a metal surface with work function 3.6 eV. Calculate the maximum kinetic energy of the emitted electrons in eV.
[3]
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Part
Answer and marking points
Marks
0.0998 eV
E = hc/λ C1 Emax = hf − φ C1 0.0998 A1
3
Question 5Structured · 10 marks
Ultraviolet radiation of wavelength 250 nm falls on a metal surface with a work function of 2.3 eV.
(a)
State what is meant by a photon.
[1]
(b)
Calculate the energy of a photon of this radiation, in joules.
[2]
(c)
Use your answer to (b) to calculate the maximum kinetic energy of the emitted photoelectrons.
[2]
(d)
Calculate the threshold frequency for this metal.
[2]
(e)
Explain why increasing the intensity of the radiation increases the photoelectric current but not the maximum kinetic energy of the electrons.
[3]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
quantum of electromagnetic energy
a discrete packet (quantum) of electromagnetic energy B1
more photons per second, more electrons; each photon energy unchanged, KE depends on f
higher intensity means more photons per second B1 so more electrons are emitted per second (larger current) B1 each photon still has energy hf, so the maximum kinetic energy is unchanged B1
3
Question 6Structured · 5 marks
Line spectra are evidence for discrete energy levels.
(a)
Explain how an emission line spectrum is produced.
[3]
(b)
A transition between levels −3.40 eV and −13.6 eV occurs. Calculate the wavelength emitted.
[2]
Show answers and mark scheme
Part
Answer and marking points
Marks
(a)
electrons drop between levels emitting photons of specific energy
electrons in atoms are excited to higher levels B1 they drop to lower levels B1 emitting photons with energy equal to the difference, so specific wavelengths B1
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Original Cambridge-style practice questions written for mentorriyaz.in. These are not Cambridge past paper questions, and this site is not affiliated with or endorsed by Cambridge University Press & Assessment. Updated 2026-11-04. Paper generator · mentorriyaz.in