A-LevelPhysicsElectric fields9702/43 · May/June 2018 · Q65 Marks
State what is meant by electric field strength.
- (a)State what is meant by electric field strength.[1]
- (b)An isolated metal sphere A of radius 26cm is positively charged. Sphere A is shown in Fig. 6.1. [Figure 6.1] Electrical breakdown (a spark) occurs when the electric field strength at the surface of the sphere exceeds 2.0 × 10⁴ Vm⁻¹. Calculate the maximum charge Q that can be stored on the sphere.[2]
- (c)A second isolated metal sphere B, also with charge +Q, has a radius of 52 cm. Calculate the additional charge, in terms of Q, that may be stored on this sphere before electrical breakdown occurs.[2]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.
- [B1] force per unit charge
- [C1] E = Q/(4πε₀r²)
- [A1] 2.0 × 10⁴ = Q / (4π × 8.85 × 10⁻¹² × 0.26²); charge = 1.5 × 10⁻⁷C
- [C1] charge (= Q [52/26]²) = 4Q
- [A1] additional charge = 3Q
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