Syllabus Edition

First teaching 2023

First exams 2025

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Uniform Electric Fields (CIE A Level Physics)

Exam Questions

50 mins5 questions
1a
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1 mark

Define electric field strength.

1b
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2 marks

A uniform electric field is produced between two vertical metal plates shown in Fig. 1.1.

7-4-s-q--q3b-easy-aqa-a-level-physics

Fig. 1.1

On Fig. 1.1, draw lines to represent the electric field between the plates.

1c
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3 marks

The metal plates are 50 mm apart. When the switch is closed, the plates are charged by a 200 V dc supply, as shown in Fig 1.2.

7-4-s-q--q3c-easy-aqa-a-level-physics

Fig. 1.2

Calculate the electric field strength between the plates when the switch is closed.

State an appropriate unit for your answer.

1d
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3 marks

A small polystyrene ball of charge –0.15 μC is suspended between the metal plates, as shown in Fig. 1.3.

7-4-s-q--q3d-easy-aqa-a-level-physics

Fig. 1.3

(i)
State the direction of the force acting on the charge.
[1]
(ii)
Calculate the magnitude of the force acting on the charge.
[2]

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2a
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3 marks

A uniform electric field is produced between two charged parallel plates, A and B. A positively charged alpha particle enters the electric field and deflects, as shown in Fig. 1.1.

7-4-s-q--q4a-easy-aqa-a-level-physics

Fig. 1.1

On Fig. 1.1,

(i)
label plates A and B with (+) or (−) to show the charges
[1]
(ii)
draw lines to represent the electric field between the plates.
[2]
2b
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4 marks

State and explain the effect on the deflection of the alpha particle when

(i)
the potential difference applied between A and B is increased
[2]
(ii)
the separation of A and B is increased.
[2]
2c
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4 marks

The alpha particle is replaced by a beta particle. The separation of the plates and the potential difference applied across them is kept the same.

State and explain two properties of alpha and beta particles that can affect the amount these particles deflect in an electric field.

2d
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2 marks

The alpha particle is replaced by a negatively charged particle which has the same mass and magnitude of charge as an alpha particle, as shown in Fig. 1.2.

The separation of the plates and the potential difference applied across them is kept the same.

7-4-s-q--q4d-easy-aqa-a-level-physics

Fig. 1.2

On Fig. 1.2, draw the path of the negatively charged particle between the parallel plates.

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1a
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2 marks

State what is indicated by the direction of the electric field line.

1b
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3 marks

Fig. 1.1 shows a pair of parallel metal plates with a potential difference (p.d.) of 3500 V between them.

 18-1-3b-m-metal-plates-electric-fields-sq-cie-a-level
Fig. 1.1
  

The plates are separated by a distance of 4.6 cm. The plates are in a vacuum. 

 

On Fig. 1.1, draw five lines to represent the electric field in the region between the plates. 

1c
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2 marks

Calculate the strength of the electric field between the plates.

 
 
electric field strength = .................................... N C−1 
1d
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2 marks

A moving electron eneters the region between the plates from the left, as shown in Fig. 1.2.

  
 18-1-3d-m-metal-plates-electron-sq-cie-a-level
Fig. 1.2
 

The electron is deflected by the electric field.

 

On Fig. 1.2, draw a line to show the path of the electron as it moves through and out of the region of the electric field.

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2a
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2 marks

Fig 1.1 shows an electron that enters an electric field at right angles to the field. 

electron-parabola

Fig 1.1

Sketch the path of the electron on Fig 1.1 once it enters the uniform electric field. State the shape of this trajectory.
2b
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2 marks

A positron enters the field at right angles instead, as shown in Fig 1.2.

18-2-m-q2b-sq-cie-ial-physics

Fig 1.2

Sketch the path of the positron on Fig 1.2.

2c
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2 marks

Fig 1.3 shows a small polystyrene ball which is suspended between two vertical metal plates, P1 and P2, distance d apart that are initially uncharged.

The ball carries a charge of –0.17 μC. 

7-4-s-q--q3b-medium-aqa-a-level-physics

Fig 1.3

When the switch is closed, a p.d. of 400 V is applied between P1 and P2 and the ball experiences an electrostatic force of 34 mN. 

Calculate the value d.

2d
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2 marks

Because of the electrostatic force acting on it, the ball is displaced from its original position. It comes to rest when the suspended thread makes an angle θ  with the vertical, as shown in Fig 1.4. 

7-4-s-q--q3c-medium-aqa-a-level-physics

Fig 1.4

On Fig 1.4, mark and label the forces that act on the ball when it is in this position.

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3a
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1 mark

An electric field exists in the space between two charged metal plates in Fig 1.1.

18-2-m-q3a-sq-cie-ial-physics

Fig 1.1

Sketch the graph on Fig 1.2 of the variation of electric field strength E  with distance d  from A along the line AB.

18-2-m-q3a2-sq-cie-ial-physics

Fig 1.2

3b
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3 marks

The force on a proton placed between the plates is 50 nN and the separation of the plates is 24 mm.

Calculate the potential difference between the plates.

3c
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4 marks

A negatively charged particle of mass 5.0 g remains stationary exactly halfway from each plate, as shown in Fig 1.3.

18-2-m-q3c-sq-cie-ial-physics

Fig 1.3

Calculate the charge of the particle.

3d
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3 marks

State and explain what will happen to the particle if the separation of the plates starts to decrease.

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