A polythene rod is rubbed with a dry cloth. The rod becomes negatively charged.
(a) Explain how the rod becomes negatively charged. [2]
(b) State the charge on the cloth after rubbing. [1]
(c) A second negatively charged polythene rod is brought close to the first rod, which is hanging freely.
State what happens to the first rod. [1]
- (a) electrons are transferred / move (by friction)(1)
- (a) from the cloth to the rod 'electrons move from the cloth to the rod' or 'the rod gains electrons from the cloth' scores both marks; 'the rod gains electrons' alone scores 1; reject any answer in which positive charges move(1)
- (b) positive (charge) allow equal and opposite charge(1)
- (c) it moves away / is repelled(1)
- Answer: (a) electrons transfer from the cloth to the rod (b) positive (c) it is repelled
- Examiner tip: Only electrons are transferred when an insulator is charged by friction: any answer about positive charges moving loses the mark.