magnets and magnetic fields Flashcards
1
Q
temporary magnets
A
- e.g. things made or iron, steel or cobalt
- temporarily become magnets when placed in a magnet field
- stop being magnets when the field leaves
2
Q
how can you tell that a magnetic field is uniform
A
- the strengths of the fields are constant
- the distance between the poles are equal
- the spacing of field lines are equal
3
Q
what is the right hand rule
A
- used to deduce the direction of the magnetic field by using the direction of the current in the wire
- (put your thumb in the direction of the conventional current)
4
Q
solenoid
A
- a long coil of wire which has a strong even magnetic field inside but weaker outside
- inside the solenoid, the fields caused by each individual coil add up to form a strong field, but outside they cancel to give a weak field
5
Q
ways to make a wire stronger
A
- increase current
- wrap in a coil
6
Q
equation for force using magnetic field strength
A
force = field x current x length of wire in magnet
7
Q
what is a tesla
A
- 1 tesla = 1 newton per amp
- the tesla is the field strength which would exert a force of 1 newton on each 1 metre of wire carrying a current of 1 amp at right angles to the field
8
Q
what is the motor effect
A
- the force experienced when you place a current-carrying wire in a magnetic field
- this force acts perpendicular to both the direction of the current and the direction of the magnet
9
Q
Flemings left hand rule
A
- used to find the direction of a force
- make a scissor shape with your left hand
- thumb = motion
- first finger = field (N to S)
- second finger = current (+ to -)
10
Q
electromagnetic induction
A
- when magnetic field lines ‘cut’ a wire and a voltage is induced in that wire
11
Q
how to increase the strength of the induced current
A
- increasing the strength of the magnet field
- increasing the speed that the wires or magnets move at
- adding more turns to our coil
12
Q
lenz’s law
A
- the induced current will flow in a direction to try to oppose the change that caused it
- e.g. if the magnet approaches north pole first, the current in the coil will flow to create a north pole to push the magnet away
13
Q
how does a transformer work
A
- the AC goes through a primary coil, and exits the secondary coil which creates a magnetic field
- the primary and secondary coil works as an electromagnet
14
Q
what does the iron core do in a transformer
A
- it carries the magnetic field from the primary coil to the secondary coil
15
Q
what is the difference between a step up and step down transformer
A
- a step up transformer has more turns on the secondary coil and so increases voltage
- a step down transformer has fewer turns on the secondary coil and so decreases voltage
