Magnetism Flashcards
What is a permanent magnet?
A magnet that has its own magnetic field
What is an induced magnet?
An object that can be magnetized by a magnetic field
What materials can a magnet be made from?
iron, steel, cobalt, nickel
What force does induced magnetism cause?
Attraction
What happens to induced magnets after the magnetic field is removed?
Lose magnetism
What is a magnetic field?
A region around a magnet where a force acts on other magnets / magnetic materials
Further away from magnetic field = ?
Weaker force
How can you find the direction of a magnetic field?
With a small compass
How can we prove the earth’s core is magnetic?
Hold a compass away from other magnets - needle will point north / south.
Current flowing though a wire produces a?
Magnetic field
How can we prove current flowing through a wire produces a magnetic field?
By holding a small compass next to the wire and turn circuit on / off - needle will point towards the circuit
What does magnetic field strength depend on in a wire?
- Current flowing through wire
What is the right hand grip rule?
Place right hand in direction of current flow - fingers will curl in the direction of the magnetic field (in a coil)
What is a coiled wire called?
Solenoid
What type of magnetic field does a solenoid produce?
A strong, uniform magnetic field on the inside of the solenoid
How can we improve the strength of a solenoid’s magnetic field?
Increase current
Increase amount of coils
Add an iron core
How many circuits does a relay contain?
2
What is the motor effect?
When a magnetic field of a wire interacts with the magnetic field of 2 other magnets, producing a force.`
What is magnetic flux density?
Strength of the magnetic field
What direction must be wire be at for the motor effect to work?
90deg to the direction of the magnetic field
How do you determine for force’s direction in the motor effect?
Using the left hand rule
What is the left hand rule?
Place thumb, 1st finger and 2nd finger at 90deg angles to each other.
Point 1st finger in the direction of the magnetic field (North - South)
Point 2nd finger in direction of current.
Thumb shows force direction
What is a split - ring commutator?
A split metal ring in contact with 2 brushes
What does the split - ring commutator do?
Changes the direction of current flow in a motor
How does a moving - coil loudspeaker work?
A cone has a coil of wire wrapped around one end
The coil is connected to an AC power supply
Current flowing through the coil generates a magnetic field, interacting the the permanent magnet on the inside of the coil.
Produces a resultant force which moves the cone
What does increasing the current do to a speaker?`
It increases the amplitude of the coil’s movements
This means that the cone is moving more air, so the sound is louder.
What is an alternator?
A coil of wire rotating in a magnetic field
What is the coil connected to in an alternator?
2 metal commutators
What is the role of a commutator?
To allow the current to pass out of a coil
When do we see the maximum potential difference in an alternator / dynamo?
When the coil moves through the magnetic field (horizontal)
When do we see no potential difference in an alternator / dynamo
When the coil isn’t moving through the magnetic field (vertical)
What causes the potential difference to reverse direction in an alternator?
When the coil starts moving in a different direction
Why does an alternator produce alternating current?
Because the coil is connected to a split ring commutator
How do we increase the size of an alternating current?
Increase magnetic field strength
Increase coil turns
Increase coil size
What happens if rotation speed is increased in an alternator / dynamo?
Amplitude of the potential difference increases
Frequency increases
Why does a dynamo produce a direct current?
It uses a split - ring commutator instead of 2 separate ones - both ends of the coil are connected to the same commutator
Sound waves hit a diaphragm, causing it to ___ ?
Vibrate
What happens to the coiled wire as the diaphragm moves (microphone)
It moves in and out of the magnetic field, inducing potential difference across the ends of the wire
What happens to the potential difference as the coil moves backwards / forwards?
It switches direction
What is the frequency of the change in potential difference equal to (microphone)
Sound wave frequency
How many coils in a transformer?
2
The primary coil is connected to an ____ ?
Alternating current
As the current flows through the primary coil, it generates a _____ .
Changing magnetic field
The changing magnetic field passes along the _____ and through the _____.
Iron core, secondary coil
Transformers only work with ______.
Alternating current
Why do transformers not work with direct current?
They produce a constant magnetic field
What is a step up transformer?
A transformer that increases voltage
What is a step down transformer?
A transformer that decreases voltage
In a transformer, power must be _____.
Conserved
