P4.1 Flashcards
What is a magnet?
Any object that has a magnetic field around it. A magnet will exert a force on a magnetic material
Behaviour of magnets?
Magnets have a N and S pole.
Like poles repel
Unlike / opposite poles attract
Direction of attraction in magnets?
Where do magnets move?
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
What is a permanent magnet?
Always has a magnetic field around it. Can attract/repel other permanent magnets, but also sometimes non-magnets
How does induced magnetism work?
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
Describe the Earth’s magnetic field
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.
Explain Earth’s geographic vs magnetic poles
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.
What happens when current flows in a wire?
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)
Describe magnetic field lines around a wire
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
How do you work out direction of magnetic field?
The Corkscrew Rule
- RIGHT hand
- Thumb points in direction of current, finger wrap around to give direction on magnetic field
What is a solenoid?
- 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.
How to increase magnetic field strength of a solenoid / electromagnet?
Increase:
1) number of coils in wire
2) size of current through wire
3) change material of core inside the coils
Relationship between field strength and distance?
Strength falls off as the square of the distance
What is magnetic field, B measured in?
Magnetic field of Earth?
Strength of mag field 1 cm from current carrying wire of 5A?
Teslas (T)
- 01 mT
- 1 mT