P4.1

Question 1

What is a magnet?

Answer 1

Any object that has a magnetic field around it. A magnet will exert a force on a magnetic material

Question 2

Behaviour of magnets?

Answer 2

Magnets have a N and S pole.
Like poles repel
Unlike / opposite poles attract

Question 3

Direction of attraction in magnets?

Where do magnets move?

Answer 3

Field lines go from N to S.
The closer / denser the field lines, the stronger the magnet. (Aka Magnetic Flux density)

In the direction that makes field lines shorten

Question 4

What is a permanent magnet?

Answer 4

Always has a magnetic field around it. Can attract/repel other permanent magnets, but also sometimes non-magnets

Question 5

How does induced magnetism work?

Answer 5

Magnetic materials are made of domains (small magnetic regions) that point in directions. When a permanent magnet is brought close, all domains line up, and magnetism is induced (early steel, iron).

Some hard magnetic materials - domains remain lined up after permanent magnet is moved
Some soft magnetic materials - domains return to original position

Question 6

Describe the Earth’s magnetic field

Answer 6

Earth behaves as if there is a huge bar magnet inside it, therefore it has a magnetic field around it, with a N and S pole that exert (small but noticeable) forces upon every magnetic material on earth.

Question 7

Explain Earth’s geographic vs magnetic poles

Answer 7

The North Pole is named so since N pole of magnets point in this direction.
Since N pole is attracted to S pole, the Earth’s geographical N pole oil actually the magnetic S pole.

Question 8

What happens when current flows in a wire?

Answer 8

A magnetic field is generated around it.

Discovery by Michael Faraday in 1830

Don’t normally notice this magnetic field around wire bc it’s very small (solenoids can increase size of mag field)

Question 9

Describe magnetic field lines around a wire

Answer 9

Exists in concentric rings

Space between consecutive field lines increase with increasing distance

If wire is carrying a greater current, fired lines closer together to show stronger magnetic field

Question 10

How do you work out direction of magnetic field?

Answer 10

The Corkscrew Rule

• RIGHT hand
• Thumb points in direction of current, finger wrap around to give direction on magnetic field

Question 11

What is a solenoid?

Answer 11

• device that acts to increase strength / size of magnetic field around a current carrying wire
• able to produce mag fields much stringer than found in natural magnets
• able to produce electromagnets
• wire looped many tines around a piece of metal (not magnet!) that can be magnetised, like iron.

Question 12

How to increase magnetic field strength of a solenoid / electromagnet?

Answer 12

Increase:

1) number of coils in wire
2) size of current through wire

3) change material of core inside the coils

Question 13

Relationship between field strength and distance?

Answer 13

Strength falls off as the square of the distance

Question 14

What is magnetic field, B measured in?

Magnetic field of Earth?

Strength of mag field 1 cm from current carrying wire of 5A?

Answer 14

Teslas (T)

0. 01 mT
1. 1 mT