Six original Cambridge-style questions on electric charge: the like and unlike rule, charging by friction in terms of electrons, conductors and insulators, and why a charged rod attracts uncharged paper.
State what happens to the force between each pair of charges.
(a) Two negatively charged spheres.
(b) A positively charged sphere and a negatively charged sphere.
(a) They repel. ✓
(b) They attract. ✓
like repel, unlike attract
An acetate rod is rubbed with a dry cloth and becomes positively charged. Explain, in terms of electrons, why the rod becomes positive and state the charge left on the cloth.
A student says, "When you rub a balloon it gains positive charge, and some of that charge then flows away through the air." Identify the two errors in this statement.
Sort the following into conductors and insulators: copper, plastic, graphite, rubber.
Conductors: copper, graphite. ✓
Insulators: plastic, rubber. ✓
A negatively charged rod is held near small pieces of uncharged paper, and the paper jumps up to the rod. The rod is not touching the paper.
Explain why the uncharged paper is attracted.
Two light balls hang side by side on insulating threads. A charged rod is used to give both balls a negative charge, and they swing apart and stay apart.
(a) State why the balls swing apart.
(b) A third ball, known to be uncharged, is brought near one of them. State and explain what is observed.
(a) Both balls carry the same (negative) charge, and like charges repel. ✓
(b) The charged ball attracts the uncharged ball, by inducing an opposite charge on its near side. ✓✓
Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.