A metal key is placed on an insulating support. Electrons carrying 3 nC3\ \mathrm{nC}3 nC of negative charge then leave the key, and its charge becomes +7 nC+7\ \mathrm{nC}+7 nC. The key is brought near an object carrying +3 nC+3\ \mathrm{nC}+3 nC. Which statement identifies the key's initial charge and predicts the interaction?
The key initially had a charge of +4 nC+4\ \mathrm{nC}+4 nC and the objects attract.
The key initially had a charge of +10 nC+10\ \mathrm{nC}+10 nC and the objects repel.
The key initially had a charge of +4 nC+4\ \mathrm{nC}+4 nC and the objects repel.
The key initially had a charge of +10 nC+10\ \mathrm{nC}+10 nC and the objects attract.
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.