6 Magnetism and electromagnetism Flashcards
What can magnets do?
- Repel and attract eachother
- Attract magnetic substances
Magnetic Materials
When placed in a magnetic field, becomes a magnet
Magnetic Elements
- Iron
- Cobalt
- Nickel
What can materials containing a magnetic element be
Magnetic or non-magnetic
Properties of magnetically hard materials
Retain magnetism when removed from a magnetic field
* Difficult to magnetise and demagnetise
e.g. steel
Properties of magnetically soft materials
Lose magnetism when removed from a magnetic field
e.g. iron
Magnetic Field Line
Represent strength and direction of a magnetic field
Features of Magnetic Field Lines
- Go from north to south
- Never cross
- Closer field lines = stronger field
Uniform Magnetic Field
Field lines are parallel and equally spaced apart
When opposite poles of 2 permanent magnets are put together
Null/neutral point
Where there is no magnetic field
When like poles of 2 permanent magnets are put together
What an electrical current in a conductor produce?
A magnetic field around it
Construction of electromagnets
- Wrap solenoid around a core
- For a strong electromagnet, core should be iron
What affects the strength of an electromagnet?
- No. of turns
- Current
What is a solenoid
A coil of wire
How to construct the field lines around a magnet
- Sprinkle iron filings
- Tap card to distribute iron filings
- Use compass to show direction of lines
- Mark where the compass points
- Move compass to multiple places and along same line
Motor Effect
When a charged particle (e.g. electron) moves in a magnetic field, there is a force.
As long as its motion is not parallel to the field
Factors that effect the motor effect
- Greater current = greater strength of magnetic field = greater force
- Reversing current or field direction = reverses direction of force
How to predict the direction of the force in a magnetic field
Flemings Left Hand Rule
* Force
* Field
* Current
Examples of when the motor effect is used
- Electric Motor
- Loudspeaker
Motor Effect: Electric Motor
- Made up of a cell which can rotate on a spindle.
- Located within a magnetic field (magnets on either side)
Motor Effect: Loudspeaker
- An alternating current flows through a coil of wire (located between the poles of a magnet) producing a magnetic field
- This interacts with the magnetic field of the permanent magnet
- Puts a force on the coil (oscillates) and causes the speaker to oscillate = longitudinal sound wave
Electromagnetic Induction
When a conductor cuts through a magnetic field, or a magnetic field changes through it = voltage is induced
Experiment: Electromagnetic Induction
Move a bar magnet in and out of a coil of wire
Coil of wire is connected to an ammeter\
- Moving magnet in and out of cell = alternating current
- Moving it in and out quicker = bigger current
- Pulling in and out = changes direction of current
How to produce an alternating current
The conductor or the magnetic field must be moving
Structure of a Transformer
2 coils linked by a core (made of a magnetic material)
How can the size of the induced voltage be increased in a transformer?
Increase:
* Speed of rotation
* Strength of magnetic field
* Number of turns on coil
* Area of coil
How a transformer works
- Primary/input coil acts as an electromagnet which produces a magnetic field
- This magnetic field induces a current in the secondary/output coil
The National Grid Structure
Power Station
Step - up Transformer
National Grid (pylons)
Step - Down Transformer
Homes
The National Grid
- To reduce power loss in transmission:
* power loss is proportional to current squared
* so high voltage is used - Wires on pylons are very high voltage (400000V)
- Too high for homes, so step - down transformer is used.
Direct Current
Current moves in a single direction
