P4.2 Flashcards
What happens when a magnetic field of a wire and a normal magnetic field interact
The wire moves in the direction to shorten the magnetic field lines.
How can you predict the movement of the wire
To predict the movement use flemings left hand rule
Thumb = force, middle finger = current, index finger = magnetic field line North to South
Description of the wires movement
The wires move up/down to shorten the field lines as a catapult field is produced as a result of the two magnetic field interacting. As there are move field lines above than below. It causes the wire to move in the direction to shorten the field lines.
How do motors work
In the first stage of the motor the left hand side moves up this is because there are more field lines below than above causing a catapult field and the wire to move up. The opposite happens to the right hand side as there are more field lines above than below causing a catapult field to form and the wire to move down and to shorten the field lines.
At 1/2 way there is no connection to the alternator so the coils stop moving but the momentum of the wires carry them forward.
The direction of the current in the coil and the commutator is reversed. And the wire that was previously going up goes down. This causes the motor to spin.
Formula of force on a wire
F = BIL
What factors affect the speed of the motor
Length of the coil
Number of coils of wire
Strength of magnetic field
Magnitude of current flowing in the coil
When is a P.D induced across a wire
A P.D is induced across the ends of the wire if the wire cuts magnetic field lines
How can you increase the V out
Moving the wire faster
Using a stronger magnetic field
Using more loops
How does an alternator work
In an alternator because of electromagnetic induction when the coil cuts through the field lines a voltage is induced in the ends of it. The induced voltage causes a current to flow. When the coil is perpendicular to the field lines the greatest amount are being cut leading to a peak voltage being generated. When it’s parallel 0V are generated. As it has slip rings there is a constant connection which means as a result A.C current/voltage is generated as current can flow in both directions.
How does a dynamo work
A dynamo works the same way as an alternator but is instead produces a D.C voltage. This is because the output is connected to a split ring commuter meaning only D.C current/voltage is produced.
How can output be increased
Using a stronger magnetic field
Using more turns in the coil
Spinning the coil faster
What do transformers do
Transformers can be used to increase or decrease a potential difference. The potential difference is induced when the magnetic field lines cutting a coil change. If you make a loop of iron with two coils you have made a transformer.
How does a transformer work
An alternating potential difference across the produces an alternating current in the primary coil.
An alternating current in the primary coil produces a magnetic field in the iron core that is always changing.
This induces a changing P.D in the secondary coil
Equation of transformers
Potential difference across primary coil/potential difference across secondary coil = number of turns in primary coil/number of turns in secondary coil
What does a step up transformer have
Has less turns in the primary coil than coils in the secondary coil
