Three tiny oil droplets, P, Q and R, carry static charge and can move freely. Droplet P is positively charged and droplet R is negatively charged. The charge on droplet Q is not known.
When P and Q are brought close together, they move away from each other.
Deduce the sign of the charge on droplet Q. Explain your answer.
Droplet Q is now brought close to droplet R. Using your answer to (a), explain whether Q and R attract or repel, and compare the sizes of the forces acting on the two droplets.
91 exam-style questions on Edexcel GCSE Physics 11.1 Charging by friction, covering 11.1.1 Charging insulators by friction, 11.1.2 Forces between charges, 11.1.3 Electrostatic phenomena, and 11.1.4 Earthing and removing charge. Each one has a worked solution and a mark scheme showing where the marks go.