The Photoelectric Effect (AQA AS Physics)

Exam Questions

3 hours43 questions
1a2 marks

The work function energy of sodium is 2.28 eV.

State what is meant by work function energy.

1b2 marks

The electronvolt is a unit of energy. 

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

1c2 marks

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

1d3 marks

Determine the threshold frequency of sodium. 

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2a6 marks

A physics teacher gives her class an excerpt which summarises the theory of the photoelectric effect, as shown in Figure 1. 

Some of the information is missing.

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She also provides a list of keywords for students to consider, as shown below: 

Intensity

Photoelectrons

Frequency

Maximum

Electromagnetic

Minimum

 

Complete the missing information in Figure 1 using keywords from the list provided. 

You may use any keyword once, more than once, or not at all.

2b3 marks

The physics teacher then asks her class to consider the equation for photoelectricity, which she writes as: 

               hf = ϕ E subscript K open parentheses m a x close parentheses end subscript 

Explain the meaning of each term in the photoelectricity equation:  

   (i)      hf

   (ii)      ϕ 

   (iii)   E subscript k open parentheses m a x close parentheses end subscript

2c2 marks

One of the students in the physics class recognises the form of the photoelectricity equation. 

They say that it looks very similar to the equation of a straight line. 

Sketch a graph of E subscript k open parentheses m a x close parentheses end subscript against f on the axes provided in Figure 2:

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2d1 mark

State the value of the gradient of the graph sketched in part (c).

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3a3 marks

The graph in Figure 1 shows how the maximum kinetic energy E subscript k open parentheses m a x close parentheses end subscript of photoelectrons released from the surface of a metal varies with the frequency f of incident light.

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Explain, with reference to both frequency and energy, why no photoelectrons are emitted when the incident light is below a frequency of 4.4 × 1014 Hz. 

3b1 mark

State the property of the graph in Figure 1 which would be used to determine a value for Planck’s constant. 

3c2 marks

Use the graph in Figure 1 to determine a value for the maximum kinetic energy, in Joules, of a photoelectron when the incident light is of frequency f = 8 × 1014 Hz. 

3d1 mark

State the experimental adjustment which could be made in order to reduce the maximum kinetic energy of released photoelectrons.

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4a1 mark

Apparatus to investigate the photoelectric effect is set up as shown in Figure 1 below:

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The incident electromagnetic radiation is above the threshold frequency of the metal photocathode. 

State what happens at the metal photocathode when the electromagnetic radiation is incident on its surface.

4b2 marks

As a result of the incident electromagnetic radiation, a photocurrent is detected in the ammeter in Figure 1. 

State what happens to the reading on the ammeter when: 

       (i)the intensity of the incident electromagnetic radiation is increased but the frequency remains constant

       (ii)the frequency of the incident electromagnetic radiation is increased but the intensity remains constant

4c3 marks

The frequency of the incident radiation is 1.4 × 1018 Hz and the work function of the metal photocathode is 2.5 eV.   

 Calculate the maximum kinetic energy of the emitted photoelectrons.

4d1 mark

Circle the sentence below which best describes where in the metal photocathode the photoelectron with the maximum kinetic energy originated from: 

Near the metal surface 

Deep within the metal

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5a3 marks

The graph in Figure 1 shows how the maximum kinetic energy K of emitted photoelectrons from a metal surface varies with the frequency f of incident light.

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Add another line to the graph in Figure 1 that shows how K will vary with f for a different metal with a greater threshold frequency.

5b1 mark

State which feature of the graph in Figure 1 is used to determine the work function of the metal.

5c2 marks

The kinetic energy of emitted photoelectrons is often measured in electronvolts. 

Define the electronvolt.

5d3 marks

Calculate the energy transferred to a photoelectron by a photon of wavelength 400 nm.

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1a4 marks

The photoelectric effect is represented by the equation  

               h f= Φ begin mathsize 20px style E subscript k end style

 Name the following terms and explain their significance in this equation:

  • h f
  • Φ
1b4 marks

A copper plate is illuminated with ultraviolet radiation of wavelength of 150 nm. The work function of copper is 5.0 eV. 

Calculate the maximum kinetic energy of the liberated electrons in eV.

1c4 marks

The radiation is maintained at the same frequency but the intensity is halved. 

 State and explain what changes, if any, occur to the number of electrons released per second and to the maximum kinetic energy of these electrons.

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2a3 marks

Calculate the longest wavelength of electromagnetic radiation that will cause photoelectric emission at a clean sodium surface. Express your answer to an appropriate number of significant figures. 

Work function of sodium Φ = 3.94 × 10–19 J. 

2b3 marks

Calculate the maximum kinetic energy of the electrons emitted when electromagnetic radiation of frequency 1.05 × 1015 Hz is incident on the surface in eV. 

2c2 marks

Explain why the kinetic energy of the emitted electrons from part (b) is a maximum value.

2d2 marks

Explain, with reference to the work function, why electrons are not emitted if the frequency of the electromagnetic radiation is below a certain value.

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3a3 marks

Figure 1 shows a photocell which uses the photoelectric effect to provide a current in an external circuit.

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Ultraviolet radiation is incident on the photo-emissive surface. It has a wavelength of 150 nm and the current is 1.8 µA. 

Give the value of the current when the intensity of the incident radiation is doubled. State and explain this effect on the current.

             

3b3 marks

There is current only if the frequency of the electromagnetic radiation is above a certain value called the threshold frequency. 

 Explain, in terms of energy, why this threshold frequency exists.

3c3 marks

The wavelength of the incident radiation is increased and at 280 nm the current falls to zero. 

Calculate the threshold frequency and the work function Φ.

3d3 marks

The student changes the material of the photoemissive surface to one with a work function of 1.7 eV. 

The frequency of the electromagnetic radiation the student now uses is 6.4 × 1014 Hz. 

Calculate the maximum kinetic energy, in J, of the electrons emitted from the photoemissive surface.

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4a2 marks

State and explain which aspect of wave-particle duality­ is demonstrated by the photoelectric effect.

4b3 marks

A particular photocell is designed to emit electrons when visible light is incident on its cathode. When orange light with wavelength 620 nm is incident on the cathode the electrons are emitted with almost zero kinetic energy. 

Calculate the work function of the cathode material in eV.

4c4 marks

Ultra-violet radiation of photon energy 4.2 × 10–19 J and of the same intensity as the visible light in part (b) is now incident on the cathode. 

Calculate the maximum velocity of the emitted electrons.

4d2 marks

State and explain the effect on the number of electrons emitted per second resulting from this change of UV radiation instead of visible light on the cathode.   

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5a2 marks

Photoelectrons are emitted from a metal surface when photons of a certain frequency hit the surface. 

State two factors that increase the maximum kinetic energy of the emitted photoelectrons.

5b3 marks

When monochromatic light is shone on a zinc surface, electrons with a range of energies up to a maximum of 5.72 × 10–20 J are released. The work function of zinc is 6.88 × 10–19 J.

Explain why the emitted electrons have a range of kinetic energies up to a maximum value.

5c3 marks

Calculate the threshold frequency of the zinc surface. Give your answer to an appropriate number of significant figures.

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1a2 marks

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

Figure 1 shows how the maximum kinetic energy K E subscript m a x end subscript  of these electrons varies with frequency f.

Figure 1

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Sketch on Figure 1 the shape of the graph that would be obtained if the experiment is repeated using metal with a greater work function.

1b3 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. Figure 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.

                        Figure 2

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

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

1c6 marks

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

1d3 marks

Suggest and explain an experimental change to the setup as shown in Figure 2 that would reduce the photocurrent measured.

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2a3 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 Figure 1 below:

                           Figure 1

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Use Figure 1 to show that the workfunction of the metal is 2.1 eV.

2b4 marks

A student uses the shape of the curve in Figure 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.

2c4 marks

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

2d4 marks

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

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3a5 marks

Figure 1a shows the apparatus used in an experiment designed to investigate the photoelectric effect. 

Light falls on to a photo-sensitive metal, and the kinetic energy of the fastest moving emitted electrons can be measured by increasing the voltage provided by the battery until the ammeter reading is zero. 

Figure 1b shows the results obtained for monochromatic light of various frequencies.

                              Figure 1a

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                           Figure 1b

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Use Figure 1b to determine the work function of the photo-sensitive metal in electronvolts.

3b4 marks

Calculate the speed of the fastest moving electron emitted by light of wavelength 500 nm

3c3 marks

The photo-sensitive metal is removed from the apparatus and irradiated with photons of energy 4 eV. Loss of electrons causes the metal to acquire a positive potential. 

What is the potential at which no further loss of electrons from the surface occurs?

Explain how you arrive at your answer.

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