Electromagnetism Flashcards
What is a permanent magnet?
A magnet that produces its own magnetic field all of the time.
What is an induced magnet?
A object that only becomes magnetic when placed inside a magnetic field.
Explain the process of plotting magnetic fields.
- Place compass at a point around a bar magnet.
- Draw a dot where the compass points.
- Move compass to this dot.
- Repeat until a full field is drawn.
What happens if an electrical current flows through a wire?
It produces a magnetic field around the wire
(Electromagnet) What happens when the direction of the current is reversed?
The direction of the field is reversed
What is a solenoid?
A coil of wire
How do you increase the magnetic field produced by a wire?
By bending a wire into a solenoid
What is the shape of a magnetic field around a solenoid similar to?
The magnetic field around a bar magnet
Electric motor: why does the wire spin?
- There is a force experienced on each side of the coil
- The forces are in opposite directions so it spins
Why do current-carrying wires experience a force inside a magnetic field?
The interaction between the field in the wire and the other magnetic field creates a force in the opposite direction.
Motor effect: how can you reverse the direction of the force?
Reverse the current or direction of magnetic field
What does the thumb represent in Fleming’s left hand rule?
Motion
What does the first finger represent in Fleming’s left hand rule?
Field
What does the second finger represent in Fleming’s left hand rule?
Current
How do electric motors work? (4 steps)
- There are magnetic fields from the permanent magnet and current in wire.
- The current is in opposite directions at each side of the coil of wire.
- So there is a force exerted - up on one side and down on the other.
- A split-ring commutator reverses the current as the motor turns so there is an equal force on each side.
How can an electric motor be made to spin faster?
By increasing the current in the coil or strength of magnetic field
How can an electric motor be made to spin in the opposite direction?
By reversing the direction of the current or magnetic field
How does the generator effect work? (5 steps)
- There is a magnetic field around the permanent magnet
- Which moves with the magnet
- The coil cuts through the magnetic field lines
- The coil is part of a complete circuit
- So a potential difference is induced and a current flows
How does a loudspeaker work? (4 points)
- An alternating current is in a solenoid, creating a magnetic field.
- The field from the current interacts with the field from the permanent magnet.
- As the current changes direction, so does the force on the coil.
- This moves a cone, causing compressions and refractions in the air - sound waves
What is the motor effect?
When a conductor placed in a magnetic field experiences a force
When is a potential difference induced across the ends of a conductor?
When the conductor is moving relative to a magnetic field or the field changes
What does ‘induced’ mean?
Created
How do you reverse the direction of an induced potential difference or induced current?
- The movement of the wire or magnetic is reversed
- The polarity of the magnetic is reversed
How does a microphone use the generator effect to create sound waves? (5 steps)
- Coil is attached to a diaphragm
- Which is placed inside a permanent magnet
- When a sound wave hits the diaphragm, it vibrates, so the coil vibrates inside the magnetic field
- Which induces a current in the coil
- The alternating p.d. induced in the coil has the same frequency as the sound waves, which causes the diaphragm to vibrate
How can you increase the strength of a magnetic field produced by a solenoid?
Putting an iron core inside of it
What does the thumb represent in Fleming’s left-hand rule?
Motion
What does the first finger represent in Fleming’s left-hand rule?
Field direction
What does the second finger represent in Fleming’s left-hand rule?
Current direction
What is magnetic flux density?
A measure of the strength of a magnetic field
