magnetism + electromagnetism Flashcards
In induced Magnete, what do the materials not have?
Fixed poles.
How can materials be made into temporary magnets?
By being ‘stroked’ with a permanent magnet.
How does stroking a material with a permanent magnet make it a temporary magnet?
As it aligns the domains in the material in all the same direction.
What does current produce around a wire?
A magnetic field.
What rule determines the direction of current?
The right hand grip rule.
Which finger points in the direction of the current in the ‘right hand grip rule’?
Thumb.
What does every other finger in the ‘right hand grip rule’ represent?
The direction of the field.
The greater the current…
The stronger the magnetic field.
The greater the distance from the wire…
The weaker the field.
Coiling the wire in a solenoid causes…
The field to align and form one giant field.
Why does the iron core in the centre of the solenoid increase its strength?
As it is easier for magnetic field lines to pass through in comparison to air.
What are 5 factors that affect strength?
~Size of current
~Length
~Cross sectional area
~Number of coils
~Soft iron core
In the motor effect, a magnet and a wire will also exert a force as…
The two magnetic fields generated by the magnet and the current in the wire interact.
What shape is the magnetic field around a wire?
Circular.
What shape is the magnetic field between two magnets?
Straight.
How does the conventional current move in Fleming’s left hand rule?
Moves in the opposite direction to the electrons.
How do you calculate force using magnetic flux density?
Force = magnetic flux density x current x length
What is magnetic flux density measured in?
Tesla and is the number of flux lines per metre squared.
How do permanent magnets lie in electric motors?
In fixed positions.
What is between the permanent magnets in an electric motor?
A coil of current carrying wire lies on an axis.
Why does an electric motor rotate?
Force on one side moves that side up and force on the other side (where current flows in the opposite direction) moves down.
When is a potential difference induced across the conductor?
When there is a relative movement between a conductor and a magnetic field.
A current flows if the conductor forms…
A complete circuit.
When the current prod yes its own magnetic field, it opposes…
The change inducing it.
When the turbine spins in an electric generator, the movement causes…
The wire to cut through the magnetic field and creates a potential difference.
When does an AC flow in an electrical generator?
When the coil of wire is connected to a complete circuit.
When is a DC produced in an electric generator?
If the ends are connected to a split ring commutator.
What does a split ring commutator reverse and why?
The current each half - rotation so the current remains positive (dynamo system).
What is produced when the cone moves in a loudspeaker?
Pressure variations which make sound.
What interacts in loudspeakers causing the coil to move?
The magnetic fields from the current and the magnet.
What is the current produced in dynamic microphones proportional to?
The sound signal.
What is at the centre of a dynamic microphone?
A fixed magnet with a coil of wire around it that is free to move.
Pressure variations in sound waves in dynamic microphones cause…
The coil to move and current is induced as it moves.
More coils on the secondary in transformers means…
It is a step up transformer as voltage will increase as the changing field will cut through more of the secondary wire inducing a larger potential difference.
Fewer coils on the secondary in transformers means…
It is a step down transformer as a smaller potential difference forms.
Number of coils on primary
——————————————- =
Number of coils on secondary
Pd of primary
———————
Pd of secondary
