Electric field strengthAQA A-Level Physics: Mind map

Exam questions on Electric field strength

1. Two horizontal metal plates in a vacuum are 0.040 m apart. They are connected to a 2.0 kV supply, producing a uniform electric field in the gap between them.
   The plate separation is doubled to 0.080 m while the supply is kept at 2.0 kV. Calculate the new electric field strength and state what happens to the force on a given charge in the gap.2 marks
2. A small metal sphere carries a charge of +4.0 nC. Its charge may be treated as a point charge at its centre, and the sphere is isolated in air (take the permittivity of air as that of free space, ε₀ = 8.85 × 10⁻¹² F m⁻¹).
   Explain, with reference to field lines, why the field strength decreases with distance from the sphere.2 marks
3. In a cathode ray tube, an electron travelling horizontally at 2.0 × 10⁷ m s⁻¹ enters the gap between two horizontal parallel plates. The plates are 0.050 m long and 0.040 m apart, and there is a uniform field of 1.5 × 10⁴ V m⁻¹ directed vertically downwards between them. Ignore gravity and edge effects. The electron has charge −1.60 × 10⁻¹⁹ C and mass 9.11 × 10⁻³¹ kg.
   Calculate the magnitude of the vertical acceleration of the electron while it is between the plates.3 marks