what is a magnetic field?
a region around a magnet where a non contact magnetic force acts on another magnet or magnetic material
what are the 4 magnetic materials?
- iron
- nickel
- cobalt
- steel
how can you describe the force between a magnet and a magnetic material?
always attractive
what is a permanent magnet?
produces its own magnetic field
what is an induced magnet?
a magnetic material that becomes a magnet when placed in a magnetic field
what is a uniform field?
one that has the same strength and direction at all points
what causes the earths magnetic field?
movement of the molten iron outer core
what is a solenoid?
a coiled current carrying wire
what is the right hand grip rule
thumb points in the direction of the north pole
fingers point in direction of current
what are three ways to increase the strength of the magnetic field around a solenoid
- increase the current
- increase the number of turns in the coil or bring the turns of the coil closer together
- inserting an iron core
how can you create an electromagnet
- coil insulated wire around iron core
- add crocodile clios onto each end of the insulated wire
- use the connecting wires to connect each crocodile clío to a terminal of the power supply
- turn on the power supply to magnetise the electromagnet
advantages of electromagnets over permanent magnets
- can be turned on and off with current
- strength can be changed by changing current
- can be easily made into a variety of shapes and less expensive to be made
answer frame for electromagnets
- circuit is complete
- current flows through wire
- a magnetic field is produced around the coil
- iron core becomes magnetised and electromagnet turns on
- electromagnet attracts…
what is an electrical motor?
uses electrical energy to produce a turning effect
motor effect sentence structure
- when current passes through a wire (or any conductor) it creates a magnetic field
- this field interacts with the permanent magnetic field
- and creates a force on the wire that is perpendicular to the direction of the current and the permanent magnetic field
explain how flemings left hand rule can be used to predict the direction a rod will move (5)
- hold thumb, first finger and second finger of left hand at right angles to eachother
- first finger represents field pointing (direction)
- second finger represents current pointing (direction)
- thumb points in direction of force
- therefore rod moves (direction)
how does an electric motor work
- when current flows through the coil, a magnetic field is created
- this field interacts with the permanent magnetic field creating a force in the sides of the coil
- sides of the coil perpendicular to the magnetic field experience w force acting in opposite directions
- causing coil to rotate
- the split ring commutator reverses the direction of current every half turn
- each half turn, the two halves of the split ring commutator swap contact from one brush to another, so the commutator reversed the current in the coil
- this keeps forces acting in the same direction
- keeping the coil rotating continuously in one direction
generator effect sentence structure:
- conductor cuts through the magnetic field/ magnetic field cuts through conductor
- changing magnetic field
- potential difference is induced across the conductor
- if the conductor is part of a complete circuit, current will flow
4 factors that change the magnitude of induced potential difference
- increase the strength of the magnetic field
- increase the speed/ motion of object
- increase the number of turns in the coil
- increase the area of the coil
2 ways to change the direction of induced potential difference
- reverse direction of motion
- reverse direction of magnetic field
why can a transformer be adjusted to have different numbers of turns on the secondary coil
- to vary the output pd
- so that you don’t need a different generator for each type of device
what is the purpose of slip rings
provides a continuous connection between / stops wires from twisting together
explain why the handle of an alternator becomes much easier to turn when power supply is disconnected
- there is no induced current
- so no magnetic field
- to oppose the movement of the coil
what is the function of a microphone?
to convert the pressure variations in sound waves into variations in current/ pd
