Physics (AS & A Level) · Feb / March 2017 · Paper 12 · Question 31

A constant potential difference is applied between two horizontal metal plates. A charged oil droplet is held stationary by the electric field between the plates. [diagram: horizontal metal plates with a charged oil droplet between them] As some of the oil evaporates, the droplet loses mass and starts to accelerate. Its charge remains constant. In which direction does the droplet accelerate, and which change needs to be made to the separation of the plates in order to stop this acceleration?

1. Adirection of acceleration: downwards; separation of the plates: decrease
2. Bdirection of acceleration: downwards; separation of the plates: increase
3. Cdirection of acceleration: upwards; separation of the plates: decrease
4. Ddirection of acceleration: upwards; separation of the plates: increase

As printed in the paper