A metal sphere has a charge of −12 nC-12\ \mathrm{nC}−12 nC. It is connected briefly to Earth and its charge becomes −5 nC-5\ \mathrm{nC}−5 nC. What has happened?
Electrons carrying 7 nC7\ \mathrm{nC}7 nC of negative charge have entered the sphere.
Electrons carrying 17 nC17\ \mathrm{nC}17 nC of negative charge have left the sphere.
Electrons carrying 7 nC7\ \mathrm{nC}7 nC of negative charge have left the sphere.
Electrons carrying 17 nC17\ \mathrm{nC}17 nC of negative charge have entered the sphere.
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.