Electromagnetism Flashcards
What direction does magnetic field always travel
North to South
What does the spacing between magnetic field lines show
The strength of the magnetic field
What magnetic field does a wire produce
a circular magnetic field
what magnetic field does a solenoid produce
one similar to a bar magnet. But the direction depends on the direction of current.
what happens to magnetic field when current is decreased through a wire
it decreases
What does the thumb represent in Fleming’s left hand rule
Motion (force)
What does the first finger represent in Fleming’s left hand rule
magnetic field
What does the second finger represent in Fleming’s left hand rule
current
What is the equation for Force in a generator
F = IBL
force(N) = current(A) x magnetic field(T) x length of wire(m)
What does B represent in physics
Magnetic flux density (Tesla)
What does L represent in physics - magnetism
Length of the wire (metres)
What is force measured in
Newtons
How can force be increased in a motor(3)
- increase the current
- increase the length of the wire
- increase the magnetic field
How do you increase the magnetism of a solenoid
Increase the number of turns/coils
What device uses the motor effect
Electric motors
What is electromagnetic induction
Inducing a current by cutting magnetic field lines with a wire/coil
If you move a wire parallel through a magnetic field will a current be produced
No
If you move a wire so that it cuts through a magnetic field will it produce current
Yes
How can you increase size of the current produced when generating electricity with a straight wire (3)
- increase the strength of the magnetic field
- increase the speed of the movement
- increase the length of wire within the magnetic field
Which hand is used for motors
Left
Which hand is used for generators
Right
How can induced current be increased in a generator (5)
- increase strength of the magnetic field
- increase the speed of rotation
- add more turns to the coil
- use a coil with a larger area
- adding an iron core to the coil
What type of current is induced from a generator
A.C.
What happens to voltage when the magnetic field is twice as strong in a generator
It doubles
What happens to voltage when the coil is spun twice as fast in a generator
- it doubles
- each half revolution is twice as fast
What do split rings do
Rotate with the coil
What do carbon brushes do
Maintain constant contact with the slip rings to transfer current to the external circuit
How is a current induced in the secondary coil of a transformer (3)
The alternating current in the primary coil produces an alternating magnetic field. This cuts through the secondary coil, inducing an alternating current.
Why are soft iron cores in transformers laminated
The magnetic field causes them to heat. This wastes energy and is less efficient. Laminations reduce heat loss.
What two coils are involved in a transformer
Primary and Secondary coils
