Electricity and magnetism, Year 7: more practice

They repel each other

HintThink about what happens to like poles.

The whyLike poles repel and unlike poles attract. This is why two north poles resist being pushed together, even though they are not touching.

Two smaller magnets, each with a north and a south pole

HintCan you ever separate one end from the other?

The whyEvery piece of a magnet has both poles, however small the piece. Cutting never separates north from south.

From the north pole to the south pole

HintLines leave one end and arrive at the other.

The whyThe arrows on field lines show the direction a free north pole would be pushed. Outside the magnet, that is away from north and towards south.

Where the field lines are closest together

HintLook at how crowded the drawn arrows are.

The whyField lines bunch up near the poles, where the magnet's push and pull is strongest, and spread out further away.

A magnetic south pole

HintUnlike poles attract.

The whyThe compass needle's north end is attracted to the Earth's pole near the geographic north, so that pole behaves as a magnetic south pole.

The steel affects the compass needle

HintWhat is the pointer sensitive to?

The whyA compass needle is a small magnet. Steel near it becomes magnetised and its field is stronger than the Earth's weak field, so the needle points the wrong way.

Negatively charged

HintElectrons carry a particular kind of charge.

The whyElectrons are negatively charged. Gaining them leaves the rod with more negative charge than positive, so it is negatively charged.

Electrons

HintOnly one kind of charged particle is free to move.

The whyOnly electrons move; the protons stay fixed in the atoms. The material that loses electrons ends up positive and the one that gains them negative.

Negative

HintWhich kinds of pair push apart?

The whyOnly like charges repel. Attraction would not prove anything, because a charged rod also attracts an uncharged one, but repulsion does.

They move towards each other

HintOpposites do something that like charges do not.

The whyUnlike charges attract. The balloons pull together without touching, so the force is a non-contact force.