Electromagnetism
What is electromagnetism?
Electromagnetism is when electric currents produce their own magnetic fields.
A fan, a printer, a fuel pump, a cassette player and a large conveyor system. What do all these have in common?
They all use electric motors to work.
Name the effect that causes a coil of current-carrying wire in an electric motor to move.
The motor effect.
What are the three vector quantities associated with Fleming’s Left-hand rule?
The magnetic field, the current, and the force.
Is the electric motor discussed here an a.c. motor or a d.c. motor?
A d.c. motor.
What can we use to observe the direction of the magnetic field surrounding an electromagnet?
Compasses can be used to show the direction of the magnetic field surrounding an electromagnet.
What is an electric motor?
An electric motor is a device that converts electrical energy to mechanical energy, usually by utilising the phenomenon known as electromagnetism.
What is the motor effect?
The Motor Effect is...
-how a current-carrying wire/coil is able to exert a force on a permanent magnet.
-how a wire/coil can exert a force on another current-carrying wire/coil near it.
-how a current-carrying wire in the presence of a magnetic field will experience a force.
What does the thumb represent?
The thumb gives the direction of the force.
Electric motors are devices that convert _____ energy into _____ energy.
electrical; mechanical
Describe what electromagnetic induction is.
Electromagnetic induction is the process of generating electric current with a magnetic field.
What is the purpose of a commutator?
To reverse the direction of current every half turn in a motor.
What formula is used to calculate the strength of the force?
Force = Magnetic Flux Density x Current x Length of Wire
What does the first finger represent?
The first finger gives the direction of the magnetic field (N to S).
Why might a current-carrying wire be placed between a magnetic field?
To produce a force from the interaction of magnetic fields.
What happens when we reverse the current in an electromagnet?
The magnetic field around an electromagnet will be reversed as well.
What are the 3 ways we can increase the speed of the rotations?
1. Increase the current
2. Add more turns to the coil
3. Increase the magnetic flux density, possibly by using a stronger magnet
Name one factor that does not affect the size of a force in on a current-carrying conductor placed in a magnetic field?
Answers may vary; example: gravity
What does the second finger represent?
The second finger gives the direction of the current (+ to -).
What are the essential features of an electric motor?
1. Coil of wire
2. Two magnets
3. Split-ring commutator
4. Two brushes (springy wires that press against both metal sections of the commutator)
What are the 4 ways to make an electromagnet stronger?
1. Increase the current that flows through the solenoid.
2. Increase the number of coils while keeping the length the same.
3. Decrease the length of the coil while keeping the number of turns the same.
4. Use an iron core as iron is a soft magnetic material.
A simple electric motor can be built using ___ between ___.
A simple electric motor can be built using a coil of wire that is free to rotate between two opposite magnetic poles.
What causes the motor effect?
A current-carrying wire exerting a force on a permanent magnet.
What is Fleming’s Left-hand rule?
A visual mnemonic device that allows people to find the direction of force/motion of the conductor in an electric motor when the magnetic field direction and the current direction are known.
Detail how an electric motor works.