Quick answer: An electric field is the region around a charge where other charges feel a force, with strength is E = F / q in N/C. This Physics 11-12 test on electric field has 8 questions worth 20 marks, to do in 45 minutes: defining field strength, two charged spheres and changing the distance. The mark scheme is on a separate page; free printable PDF.
This test covers field strength, Coulomb’s law, uniform fields, potential and energy. Use k = 8.99 × 10⁹ N m²/C², e = 1.60 × 10⁻¹⁹ C and me = 9.11 × 10⁻³¹ kg. Show your working and give each result with its unit.
Level: Physics grades 11-12 (A Level · IB · Class 11-12) · Curriculum: IB D.2
Question 1 Defining field strength (2 marks)
Define electric field strength and state one unit for it.
Question 2 Two charged spheres (3 marks)
A +5.0 nC sphere and a −3.0 nC sphere are 6.0 cm apart in air.
- Calculate the magnitude of the force between them. (2 marks)
- State whether the force is attractive or repulsive and explain why. (1 mark)
Question 3 Changing the distance (2 marks)
The force between two point charges is 1.8 × 10⁻³ N when they are 2.0 cm apart. Calculate the force when they are 6.0 cm apart.
Question 4 Field between plates (3 marks)
Two parallel plates 3.0 cm apart have a potential difference of 900 V.
- Calculate the electric field strength between them. (1 mark)
- Calculate the force on a 1.5 nC charge between the plates. (2 marks)
Question 5 Field lines (2 marks)
Explain why two electric field lines can never cross, and what the spacing of the lines shows.
Question 6 Electron gun (3 marks)
An electron is accelerated from rest through a potential difference of 2.5 kV.
- Calculate the kinetic energy gained, in joules. (1 mark)
- Calculate the speed of the electron. (2 marks)
Question 7 Potential between plates (2 marks)
The diagram shows two plates with potentials of 80 V (top) and 0 V (bottom).
Calculate the potential at P and the field strength between the plates.
Question 8 Potential of a point charge (3 marks)
A small sphere carries +5.0 nC.
- Calculate the electric potential at 0.25 m from its centre. (2 marks)
- Calculate the work needed to bring a proton from infinity to that point. (1 mark)
