CAPE Physics Unit 2 · 2006 · Paper 2 · Question 3(a)(iii)

A Millikan's oil drop experiment where a droplet is held stationary between two parallel horizontal plates when mg = qE.

To hold the drop stationary when the charge changes the p.d. must be adjusted. Draw a diagram of a circuit which could be connected to P and Q to achieve this, assuming that a power supply with a fixed output of 400\text{ V d.c.} is available.

This question uses a figure or table from the paper — you'll see it when you practise.