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CIE Physics GCSETopic 4.6 - Electromagnetic Effects
Flashcards
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What is electromagnetic induction?
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What is electromagnetic induction?
The production of a potential difference caused by relative movement between a conductor and a magnetic field.
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In what direction is the potential difference induced? (supplement)
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In what direction is the potential difference induced? (supplement)
In the opposite direction to the movement which produced it.
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When is a current produced?
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When is a current produced?
When the ends of the coil are connected to a complete circuit.
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How can you increase the induced EMF?
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How can you increase the induced EMF?
● Moving the wire more quickly● Increasing the length of wire● Using a stronger magnetic field
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How can you work out the direction of the induced current? (supplement)
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How can you work out the direction of the induced current? (supplement)
Using Fleming’s right hand rule.
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How are electrical generators set up?
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How are electric generators set up?
In the same way as a motor, with a rectangular loop of wire between permanent magnets. The main difference is the presence of a turbine to spin the coil.
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Describe how an electrical generator works
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Describe how an electrical generator works
● A turbine spins the coil of wire between the magnets.
● The wire cuts through the magnetic field, experiencing a changing magnetic field.
● A potential difference is induced.● A current is produced.
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What kind of current is produced by an ordinary generator?
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What kind of current is produced by an ordinary generator?
An alternating current.
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How does a split ring commutator work? (supplement)
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How does a split ring commutator work? (supplement)
It disconnects and reconnects the wires every half rotation, switching the current so the motor spins continuously.
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How do transformers work?
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How do transformers work?
● An alternating current flows through the primary coil, producing an alternating magnetic field.
● This causes the secondary coil to experience a changing magnetic field, inducing a potential difference, which produces an alternating current in the secondary coil.
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Why do step up transformers increase voltage?
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Why do step up transformers increase voltage?
There are more coils experiencing the change, so a larger p.d. is induced.
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State one assumption used in transformer calculations (supplement)
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State one assumption used in transformer calculations (supplement)
The transformer is 100% efficient (the power is assumed to be the same in both coils).
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Give the transformer equations linking number of coils, p.d. and current
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Give the transformer equations linking the number of coils, p.d. and current
N₁
N₂
I₂
I₁
V₁
V₂= =
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What is produced around a current carrying wire?
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What is produced around a current carrying wire?
A magnetic field.
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How can you determine the direction of a magnetic field around a wire?
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How can you determine the direction of a magnetic field around a wire?
Using the Right Hand Grip Rule. Produce a thumbs-up shape with your right hand and point your thumb in the direction of the flow of current. The field lines wrap around in the direction of your fingers.
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What is a solenoid?
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What is a solenoid?
A coil of wire with a magnetic field, which can be used as an electromagnet.
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How does coiling a wire affect the magnetic field?
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How does coiling a wire affect the magnetic field?
It increases the field strength, as the magnetic fields of each turn of wire are added together.
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How can you increase the strength of a solenoid magnet?
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How can you increase the strength of a solenoid magnet?
● Using an iron core to carry field lines (as they travel more easily through metal than air)
● Increase the number of turns in the coil● Increase the current
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What is the motor effect?
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What is the motor effect?
If a current-carrying wire is placed in a magnetic field it experiences a force, pushing the wire out of/away from the field.
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Describe the mechanism of the motor effect
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Describe the mechanism of the motor effect● When a current-carrying wire produces a
magnetic field within the field of a permanent magnet, the two fields interact.
● The wire experiences a force pushing it away from the magnetic field, at right angles to the direction of the permanent field and the current.
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How can you predict the direction of the motor effect? (supplement)
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How can you predict the direction of the motor effect? (supplement)
Using Fleming’s left hand rule.Thumb = MovementFirst finger = FieldSecond finger = Current
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What is conventional current? (supplement)
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What is conventional current? (supplement)
A model for current which flows in the opposite direction to electrons. Conventional current flows from positive to negative.
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What kind of current is used in Fleming’s rule? (supplement)
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What kind of current is used in Fleming’s rule? (supplement)
Conventional current.
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Which factors affect the strength of the motor force?
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Which factors affect the strength of the motor force?
● The length of wire placed in the field● The current in the wire● The strength of the permanent field
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