Electric fields and Coulomb's lawEdexcel A-Level Physics: Subtopic test

1. 1
   A small sphere carries a charge of +2.0 nC. When it is placed at a point P in an electric field it experiences a force of 6.0 × 10⁻⁵ N.

   (a)

   Which statement correctly defines an electric field?

   [1 mark]

   • AA region where a mass experiences a force
   • BA region where an electric current flows
   • CA region where a charged particle experiences a force
   • DThe energy transferred per unit charge

   (b)

   The sphere is replaced by a sphere carrying a charge of −2.0 nC at the same point P. Which row describes the force on it?

   [1 mark]

   • ASame magnitude, opposite direction
   • BSame magnitude, same direction
   • CTwice the magnitude, same direction
   • DZero

   (c)

   Calculate the electric field strength at P.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Two small charged spheres, X and Y, carry charges of +3.0 nC and +5.0 nC. They are in a vacuum with their centres 0.060 m apart. The spheres may be treated as point charges.

   (a)

   Which statement about the electrostatic force between X and Y is correct?

   [1 mark]

   • AIt is attractive and larger on the 5.0 nC sphere
   • BIt is attractive and equal on both spheres
   • CIt is repulsive and larger on the 5.0 nC sphere
   • DIt is repulsive and equal in magnitude on both spheres

   (b)

   The spheres are moved so that their separation is doubled to 0.12 m. What is the force between them now compared with the original force?

   [1 mark]

   • AOne half
   • BOne quarter
   • CTwice
   • DFour times

   (c)

   Calculate the magnitude of the force between X and Y.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A point charge of +6.0 nC is fixed in a vacuum. A student investigates the electric field around it at a point Q that is 0.15 m from the charge.

   (a)

   Calculate the electric field strength at Q and state its direction.

   [3 marks]

   (b)

   A proton is released from rest at Q. Calculate the initial force on the proton and its initial acceleration.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Two small identical metal spheres, A and B, each carry the same positive charge. Sphere A is held in a fixed position. Sphere B has a mass of 2.0 × 10⁻³ kg and floats in equilibrium directly above A, with the centres of the spheres 0.040 m apart. B is supported only by the electrical repulsion. The spheres may be treated as point charges.

   (a)

   Calculate the charge on each sphere. Hence calculate the separation at which a sphere of twice the mass of B would float in equilibrium above A, if A and B carry the same charges as before.

   [6 marks]

   (b)

   Sphere B is nudged slightly upwards and released. Explain what happens to B, and comment on one assumption made in applying Coulomb's law to this situation.

   [6 marks]

   Total for question 4: 12 marks

End of questions