Charge and electric fields
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 1 worked example, 4 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- The balloon and the hair
- Two kinds of charge
- Charging by friction
Read the transcript of the teaching part
Last time
Before we start: last time, in Magnets, poles and magnetic fields, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
The balloon and the hair
Rub a balloon on your hair, and it sticks to the wall. Your hair stands on end, and sometimes you get a tiny spark. Nothing seems to have changed, but tiny particles have moved, and that has given the balloon an electric charge.
Two kinds of charge
There are two kinds of electric charge, positive and negative. Atoms contain positive protons and negative electrons. Normally an atom is neutral: it has equal numbers of protons and electrons. Like charges repel. Unlike charges attract.
Charging by friction
When two insulators are rubbed together, electrons are transferred from one to the other. The protons do not move. The material that gains electrons becomes negatively charged. The one that loses electrons becomes positively charged. The two objects end up with equal and opposite charges, so the total charge is the same as it was before.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Electric fields · Charge and charging by friction · Electric fields.
The whole chapter: Electrical Quantities, Electrical Quantities.
Chapter 4.2: Electrical quantities
- Charge and electric fields 5 min
- Electric current, d.c. and a.c. 5 min
- E.m.f., potential difference and cells 6 min
- Resistance and Ohm's law 5 min
Also for O Level Physics 5054
Which topics come up most in O Level Physics 5054 past papers, counted from every paper since 2004.