A-LevelPhysicsElectric fields9702/42 · Oct/Nov 2019 · Q98 Marks
Define what is meant by electric potential at a point.
- (a)Define what is meant by electric potential at a point.[2]
- (b)(i)the initial kinetic energy E_K, in J, of an α-particle emitted from the source E_K = ..................................................... J [1][1]
- (b)(ii)the distance d of closest approach of an α-particle to a gold nucleus. d = ..................................................... m [4][4]
- (c)Use your answer in (b)(ii) to comment on the possible diameter of a gold nucleus.[1]
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 (Oct/Nov 2019). The mark or mark type is shown in brackets.
- [B1] work done per unit charge
- [B1] (work done) moving positive charge from infinity
- [A1] energy = 4.8 × 1.60 × 10⁻¹³ = 7.7 × 10⁻¹³ J
- [C1] E_p = Qq / 4πε₀d
- [C1] Q=79e and q=2e
- [C1] 7.68 × 10⁻¹³ = (79 × 2 × {1.60 × 10⁻¹⁹}² / (4π × 8.85 × 10⁻¹² × d)
- [A1] d = 4.7 x 10⁻¹⁴ m
- [B1] (diameter must be) less than/equal to 10⁻¹³ or 10⁻¹⁴ m
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