Electric potential and field patternsEdexcel International A Level Physics: Subtopic test

1. 1
   Two large, flat, parallel metal plates are 4.0 cm apart in a vacuum. A potential difference of 600 V is maintained between them, with the upper plate positive.

   (a)

   Which statement describes the electric field in the region between the plates, away from the edges?

   [1 mark]

   • AIt is uniform, with parallel and equally spaced field lines
   • BIt is radial, with field lines that spread out from the upper plate
   • CIt is strongest next to the positive plate and weakest next to the negative plate
   • DIt is zero in the middle and largest near each plate

   (b)

   What is the magnitude of the electric field strength between the plates?

   [1 mark]

   • A24 V m⁻¹
   • B15 V m⁻¹
   • C3.8 × 10⁵ V m⁻¹
   • D1.5 × 10⁴ V m⁻¹

   (c)

   A proton is placed in the field between the plates. Calculate the force on the proton and state its direction. (Charge of a proton = 1.60 × 10⁻¹⁹ C.)

   [2 marks]

   Total for question 1: 4 marks

2. 2
   An isolated small sphere carries a charge of +8.0 nC in a vacuum. Its charge may be treated as a point charge at its centre.

   (a)

   What is the electric potential at a distance of 0.20 m from the centre of the sphere?

   [1 mark]

   • A1.8 × 10³ V
   • B360 V
   • C72 V
   • D180 V

   (b)

   What is the electric potential at a distance of 0.10 m from the centre of the sphere?

   [1 mark]

   • A90 V
   • B180 V
   • C720 V
   • D1440 V

   (c)

   Calculate the work done by an external force in moving a +2.0 nC charge slowly from 0.40 m to 0.20 m from the centre of the sphere.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Along a straight line in a region of electric field, the potential falls uniformly from 240 V at a point X to 80 V at a point Y. The distance XY is 0.040 m.

   (a)

   Calculate the electric field strength between X and Y, assuming it is uniform, and state its direction.

   [3 marks]

   (b)

   A charge of +3.0 nC moves from X to Y. Calculate the change in its electric potential energy and state whether the energy increases or decreases. Explain what happens to this energy if no other forces act on it.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An isolated charged metal sphere of radius 5.0 cm carries a charge of +5.0 nC in a vacuum. Its charge may be treated as if it were all at the centre of the sphere.

   (a)

   Describe the field lines and equipotentials around this sphere and compare them with those in the uniform field between two parallel charged plates. Explain how the diagrams show where the field is strongest.

   [6 marks]

   (b)

   Calculate the potential at the surface of the sphere and at a point 0.20 m from its centre. Hence find the work done in moving a +1.0 nC charge from the 0.20 m point to the surface. Calculate the electric field strength at the surface and state whether the potential energy of the charge increases or decreases.

   [6 marks]

   Total for question 4: 12 marks

End of questions