7. Electricity & Magnetism Flashcards
What is a magnetic field?
A region of space where magnetic material can experience a force
What type of poles attract?
Unlike poles
What type of poles repel?
Like poles
What is inside a compass?
A tiny bar magnet
How does a compass show that the earth generates its own magnetic field?
When the compasses are not near a magnet they point north
Which direction do field lines point in?
North to South
What does it mean when field lines are closer together?
They are stronger
Do field lines ever touch or cross?
No
Where is the magnetic field strongest?
At the poles of the magnet
What do the direction of the field lines show?
The direction of the force that would act on a tiny N-pole placed at that point
What are magnetic materials made of?
Molecular magnets
What are molecular magnets?
Tiny magnets with N and S poles
What are domains?
Groups of molecular magnets
How are the molecular magnets when a material is unmagnetised?
The unmagnetised domains point in random directions
How are the molecular magnets when a material is magnetised?
Most molecular magnets are aligned
What does saturated mean when talking about a magnet?
When all molecular magnets are aligned
What happens when a magnet breaks?
Two magnets are simply made
Is iron a soft or hard magnetic material?
Soft
What are the properties of a soft magnetic material?
- easy to magnetise
* will demagnetise easily (so useful in electromagnets)
What type of magnetic material is used for electromagnets?
Soft
Why is soft magnetic material used in electromagnets?
It is easy to magnetise and demagnetise
Is steel a hard or soft magnetic material?
Hard
What are the properties of a hard magnetic material?
- harder to magnetise
* also hard to demagnetise
What is hard magnetic material used for?
Permanent magnets e.g. needles in compasses
What is an electromagnet?
A solenoid with an iron core inside
What is a solenoid?
A coil of wire
What happens when a current is passed along the wire in an electromagnet?
A magnetic field is created and as a result the iron core is magnetised
What happens in an electromagnet when the current is switched off?
The iron bar loses it’s magnetism because it’s a temporary magnet
What can the strength of the magnetic field in an electromagnet be increased by?
- increasing the voltage or decreasing the resistance - to INCREASE THE CURRENT
- increasing the number of turns on the coil
- inserting an iron core
Where are electromagnets used?
- cranes
* in hospitals dealing with eye injuries - remove steel splinters
How does an electric bell work?
- bell-push completes circuit and current flows through electromagnet
- iron is attracted towards electromagnet and hammer hits gong
- movement breaks circuit so current stops and electromagnet is switched off
- spring pulls iron back so contact is made and sequence repeats
When will a wire NOT experience a force when placed in a magnetic field?
If it’s parallel to the direction of the field
