# Electromagnetic Induction

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• Created by: LZ95
• Created on: 17-04-14 21:31
What is electromagnetic induction?
When a wire cuts across the lines of a magnetic field, causing an induced emf
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What is the induced emf increased by?
Moving the wire faster, using a stronger magnet and making the wire into a coil
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In which two situations does the emf become 0?
1. When the wire is parallel to the field lines 2. When the motion between the wire + magnet stops
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When a road with free electrons is passed through a magnetic field, what happens to the electrons?
They are moved to one end of the rod, away from the other end, by the magnetic force.
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When working out the direction of the force in this situation, which rule would you use?
Fleming's right hand rule
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What does the rate of transfer of energy from the source of emf to other components equal to?
Product of induced emf and current
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Induced emf in a circuit = rate of change of flux linkage through the circuit
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What must the relationship be between the applied and magnetic force to keep a conductor moving through the field?
Applied force must be equal and opposite to magnetic force.
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Which way does the current pass in a North Pole?
Anticlockwise
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Which way does the current pass in a South Pole?
Clockwise
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What is Lenz's law?
Direction of the induced current is always such as to oppose the change that caused the current.
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What is the unit for magnetic flux?
Weber (Wb)
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Name 4 ways in which peak emf can be increased
Increasing the speed, using a stronger magnet, using a larger coil and increasing the no. of turns of coil
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Why is the induced emf referred to as the 'back emf'?
As it acts against p.d.
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What are the emf and current like at low speed?
Current = high, emf = low
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What are the emf and current like at high speed?
emf = high, current = low
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What is a typical A.C. generator?
A rectangular coil spinning in a uniform magnetic field.
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When is the max emf achieved?
When the sides of the coil cut at right angles along the field lines
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What does a transformer do?
Changes an alternating p.d. to a different peak value
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What does a transformer consist of?
A primary and a secondary coil, wrapped around the same iron core.
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What happens when the primary coil is connected to a source of alternating p.d.?
Alternating magnetic field is produced in the core, passing through the secondary coil.
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What does the changing magnetic field produce in the secondary coil?
An alternating emf
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What are the properties of a step up transformer?
Voltage is stepped up and current is stepped down, as there are more turns on the secondary coil
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What are the properties of a step down transformer?
Voltage is stepped down and current is stepped up, as there are more turns on the primary coil
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Name 3 ways in which a transformer can be made more efficient
Low resistance windings, laminated core and soft iron core
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How do low resistance windings improve efficiency?
They reduce the power wasted due to the heating effect of the current
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How does a laminated core improve efficiency?
Induced currents (eddy currents) reduced so magnetic flux is as high as possible.
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How does a soft iron core improve efficiency?
It is easily magnetised + demagnetised which reduces the power wasted in repeated magnetisation + demagnetisation of the core
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At what frequency and voltage does the national grid generate A.C.?
50Hz and 25kV
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## Other cards in this set

### Card 2

#### Front

What is the induced emf increased by?

#### Back

Moving the wire faster, using a stronger magnet and making the wire into a coil

### Card 3

#### Front

In which two situations does the emf become 0?

### Card 4

#### Front

When a road with free electrons is passed through a magnetic field, what happens to the electrons?

### Card 5

#### Front

When working out the direction of the force in this situation, which rule would you use?