Electric Charges and Fields

Lesson

Part 1 — where electric charge comes from, how charges push and pull, and the field that carries the push.

In this lesson you will

Concept

Frictional electricity

Rubbing two different materials together transfers electrons from one to the other:

The material that gains electrons becomes negative; the one that loses them becomes equally positive.
A glass rod rubbed with silk becomes positive; an ebonite rod rubbed with fur becomes negative.
Only electrons move: the positive nuclei stay fixed in the materials.

Concept

Charges are of two kinds, positive and negative: like charges repel, unlike charges attract.

Conductors (metals, the human body, salt water) have charges free to move through them.
Insulators (glass, plastic, dry air) hold their charges in place where they are put.
A charged rod picks up bits of paper because it pulls their charges slightly apart (polarises them) and then attracts the nearer, opposite side.