Syllabus Edition

First teaching 2023

First exams 2025

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Photoelectric Effect (CIE A Level Physics)

Exam Questions

1 hour8 questions
1a
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2 marks

In an experiment to investigate the photoelectric effect, a beam of photons is incident on the surface of a metal.

State what is meant by the term photon.

1b
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3 marks

The photoelectric equation is given by:

h f space equals space ϕ space plus space 1 half m v squared subscript m a x end subscript 

Explain the meaning of each term in the photoelectric equation:

(i)
h f
[1]
(ii)
ϕ
[1]
(iii)
1 half m v squared subscript m a x end subscript
[1]
1c
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3 marks

Outline how the photon model of light is used to explain the photoelectric effect.

1d
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3 marks
(i)
Sketch a graph of E subscript K left parenthesis m a x right parenthesis end subscript  against f on the axes provided.
[2]

qu2c-fig-2

 

(ii)
State the quantity represented by the gradient of the graph.

[1]

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2a
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1 mark

Photons are emitted from an ultraviolet (UV) lamp and are incident on a metal photocathode.

Outline what happens at the metal photocathode when the photons are incident on its surface.

2b
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2 marks

No photoelectron emission is observed from the metal surface when the incident light is below a certain frequency.

Outline why the wave theory for light cannot explain this observation.

2c
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4 marks

The work function of the metal in the photocathode is 2.4 eV.

Outline what is meant by

(i)
work function
[2]
(ii)
threshold frequency
[2]
2d
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4 marks

The energy of the incident UV photons is 10.2 eV.

Calculate:

(i)
The threshold frequency of the metal.
[2]
(ii)
The maximum kinetic energy, in J, of the emitted electrons.
[2]

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3a
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2 marks

The work function of sodium is 2.28 eV.

State what is meant by work function.

3b
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2 marks

The electronvolt is a unit of energy. 

Show that 2.28 eV is equivalent to 3.65 × 10–19 J.

3c
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2 marks

State what is meant by the threshold frequency of a metal.

3d
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3 marks

Calculate the threshold frequency of sodium. 

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1a
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2 marks

Describe two phenomena associated with the photoelectric effect that cannot be explained using a wave theory of light.

1 ....................................................................................................................

2 ....................................................................................................................

1b
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5 marks

The maximum energy Emax of electrons emitted from a metal surface when illuminated by light of wavelength λ is given by the expression

            E subscript m a x end subscript equals h c open parentheses 1 over lambda minus 1 over lambda subscript 0 close parentheses

where h is the Planck constant and c is the speed of light.

(i)
Identify the symbol lambda subscript 0.

[1]

(ii)
The variation with 1 over lambda of Emax for the metal surface is shown in Fig. 8.1.

q8b-ii-paper-4-specimen-2022-cie-ial-physics

Fig. 8.1

Use Fig. 8.1 to determine the magnitude of λo.



λo
= ....................................... m [1]

(iii)
Use the gradient of Fig. 8.1 to determine a value for the Planck constant h. Show your working.





h
= ................................. J s [3]

1c
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2 marks

The metal surface in (b) becomes oxidised.

Photoelectric emission is still observed but the work function energy is increased.

On Fig. 8.1, draw a line to show the variation with 1 over lambda of Emax for the oxidized surface.

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2a
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2 marks

State what is meant by a photon.

2b
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5 marks

Electromagnetic radiation of a varying frequency f and constant intensity I is used to illuminate a metal surface. At certain frequencies, electrons are emitted from the surface of the metal.  

(i)
State the name of this phenomenon.
[1] 
(ii)
The variation with f of the maximum kinetic energy EMAX of the emitted electrons is shown in Fig. 1.1.
7ssNjDy__22-1-2b-m-photoelectric-effect-energy-frequency-graph-cie-ial-sq
Fig. 1.1
 

Describe four conclusions that can be drawn from the graph in Fig. 1.1. The conclusions may be qualitative or quantitative.  

[1]

2c
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4 marks

The experiment in (b) is carried out twice more. Each time one change is made to the method used. 

State, and explain, how the graph obtained would compare with Fig. 1.1. when: 

(i)
the same metal is used, but with electromagnetic radiation of intensity I over 2
 
[2]
(ii)
a different metal is used, but the intensity of the radiation is the same.
 
[2]

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3a
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2 marks

State what is meant by the work function energy of a metal.

3b
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2 marks

Ultraviolet radiation of frequency 8.5 × 1014 Hz is incident, in a vacuum, on a metal surface. The power of the radiation incident on the surface is 9.45 mW. Photoelectrons are emitted with a maximum kinetic energy of 2.1 × 10–19 J. 
Determine the number of photons incident on the surface per unit time.

 
number per unit time = ...................................... s−1
3c
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2 marks

Calculate the work function energy Φ of the metal.

 
Φ = ....................................... J 
3d
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3 marks

The frequency of the radiation incident on the surface in (b) is decreased while the power remains constant 

State and explain the effect of this change on: 

(i)
the maximum kinetic energy of the photoelectron
 
[2]
(ii)
the rate of emission of the photoelectron.
 
[1]

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1a
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2 marks

When electromagnetic radiation of frequency f is incident on a particular metal surface, photoelectrons are emitted. 

Fig. 1.1 shows how the maximum kinetic energy K E subscript m a x end subscript  of these electrons varies with frequency f.

2-4-s-q--q2a-hard-aqa-a-level-physics

Fig. 1.1

Sketch on Fig. 1.1 the shape of the graph that would be obtained if the experiment is repeated using metal with a greater work function.

1b
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3 marks

A certain metal with a work function of 2.2 eV is selected to create two parallel plates. These are connected in a circuit to a sensitive ammeter and a power source, such that a uniform electric field of 140 N C–1 exists between them. Fig. 1.2 shows the two plates, labelled A and B, separated by 25 mm in a vacuum. 

Electromagnetic radiation of wavelength 255 nm is incident on plate B, such that photoelectrons are emitted from B and move towards A. The ammeter detects a photocurrent in the circuit.

2-4-s-q--q2b-hard-aqa-a-level-physics

Fig. 1.2

State the direction of the electric field between the plates, given the photocurrent is at a maximum.

Explain your answer.

1c
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6 marks

Show that the maximum possible speed of the photoelectrons as they reach plate A is approximately 1.5 × 106 m s–1.

1d
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3 marks

Suggest and explain an experimental change to the circuit, part of which is shown in Fig. 1.2, that would reduce the photocurrent measured.

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2a
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3 marks

The maximum kinetic energy, K E subscript m a x end subscript  of photoelectrons varies with the wavelength of incident light on a metal surface. This is shown in Fig. 1.1 below:

2-4-s-q--q3a-hard-aqa-a-level-physics

Fig. 1.1

Use Fig. 1.1 to show that the work function of the metal is 2.1 eV.

2b
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4 marks

A student uses the shape of the curve in Fig. 1.1 to state that maximum kinetic energy is inversely proportional to the incident wavelength.

By referring to the photoelectricity equation, discuss the validity of this statement.

2c
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4 marks

Calculate the de Broglie wavelength of photoelectrons emitted from the metal surface for incident light of wavelength 500 nm. 

2d
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4 marks

Discuss the experimental changes that would reduce the minimum de Broglie wavelength of the emitted photoelectrons.

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