P7 Flashcards
Magnetic field
The area where a force acts on another magnet or magnetic material
Poles
The place on a magnet where the magnetic force is the strongest
Like poles
repel
Unlike poles
attract
Permanent magnet
Produces its own magnetic field
Induced magnet
A material that becomes magnetic when placed in a magnetic field
Magnetic metals
iron, cobalt, nickel and steel
The force between a magnet and a magnetic material
always attraction
Direction of magnetic field lines
North to south
Magnetic compass
Works by using the earths magnetic field facing the bar magnet towards the north
How to plot magnetic field patterns
Place a magnet on an A4 paper, move a compass equal distances and plot where the pin faces
How is a magnetic field produced around a wire?
A current is induced.(The stronger the current the syringe the magnetic field)
How to increase the strength of a magnetic field through a wire
Coil it making it a solenoid
Magnetic field in a solenoid
Strong and uniform
Electromagnetic
a solenoid with a soft iron core
Magnetic field around a solenoid
A similar shape to a bar magnet
Fleming left had rule
Thumb = force
Index finger = magnetic field
Middle finger = Current direction
Electric motor
a coil of wire carrying a current will have a rotating magnetic field( right hand thumb rule)
Alternator
produces AC
Dynamo
Produces DC
Magnetic field of an induced current
opposes the original change
Factors affecting the size of the induced potential difference/current
Speed of the magnets movement or size of the magnetic field
How to reverse the direction of an induced current
change the direction of the magnets movement or magnetic field
Use of the generation affect
In dynamos or alternators
Microphones
Use the generator effect to convert the pressure variations in sound waves to variations in electrical circuit’s
Transformer
Has a primary and secondary coil to step up or down the current and P.D respectively
Why is an iron core used in transformers
it is easily magnetised
What determines the ratio of P.D over transformer coils
The ratio of turns on each coil
Step-up transformer
Vs > Vp
Step-down transformer
Vs < Vp
Vp and Vs
Primary voltage and the secondary voltage
np and ns
Primary number of coils and secondary number of coils
100% efficient transformer
Electrical input is the same as the electrical output
How a transformer works
- AC flows through the primary coil
- This AC induces and alternating magnetic field
- The alternating magnetic field in the iron core induces alternating PD in the secondary coil
- AC flows through the secondary coil
Magnetic flux density
The strength of a magnetic field measured in Tesla (T)
Solenoid
long straight coil of wire
