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Physics > Electromagnetism (Chapter P5/P15) > Flashcards

Electromagnetism (Chapter P5/P15) Flashcards

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1
Q

What is a magnetic field

A

A region around a magnet where magnetic materials experience attractive magnetic forces

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2
Q

How do you make a stronger electromagnet

A

More turns of wire on the coil
Add an iron core
Use a larger current

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3
Q

What is a solenoid

A

A long coil of insulated wire which produces a strong magnetic field

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4
Q

What is a use of a electromagnet

A

Electric bell

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5
Q

what is a relay

A

A switch operated by an electromagnet

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6
Q

What is the motor effect

A

It is when a force is exerted on a wire when between magnets and carrying a current

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7
Q

How can we predict the motor effect

A

The left hand rule

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8
Q

How does an electric motor work

A

The force between the 2 magnetic fields from the magnets and the wire cause the coil to turn.
The commutator allows the coil to fully spin in 1 direction

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9
Q

How do you reverse the spin of a motor

A

Change the direction of the current

Switch the magnets around

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10
Q

How does a loud speaker work

A

A coil of wire wrapped around a tube is placed over the north pole magnet.
The alternating current means that the direction of the coil is changing.
This causes the coil to create sound waves

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11
Q

what is the equation for force involving magnetic flux density

A 
Force = Magnetic Flux Density x Current x Length of Wire
F = B x I x L
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12
Q

What is electromagnetic induction

A

It is the creation of current by moving magnets near a circuit

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13
Q

How can you increase the current induced by electromagnetic induction

A

Changing the speed of the magnet
Using a stronger magnet
Use more coils

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14
Q

What is an alternator

A

It is a machine which uses the motor effect to create a alternating potential difference

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15
Q

How does an alternator work

A

The coil rotates between two magnets and every half cycle the slip rings change charge and the current flows the opposite direction in the circuit

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16
Q

What is a dynamo

A

It is a machine that uses the generator effect to create a direct current

17
Q

How does a dynamo work

A

The coil rotates between two magnets and instead of slip rings there is a commutator.
The commutator keeps the two connections the same charge and so creates a direct current

18
Q

What are the similarities between a dynamo and an alternator

A

Both use the generator effect
Both use a conductor passing through a magnetic field
Both create a current from a potential difference

19
Q

What are the differences between a dynamo and an alternator

A

The dynamo generator uses split rings instead of slip rings
The dynamo generator creates a direct current instead of an alternating current
A alternator’s arm of coil reverses every 180 degrees of rotation whereas the dynamos generator’s split rings lose contact every 180 degrees of rotation

20
Q

what is a transformer

A

It is a machine which changes the current across a wire

21
Q

How does a transformer work

A

An a.c. current in the primary coil creates a changing magnetic field in the iron core
This magnetic filed goes through the secondary coil and induces a potential difference across it
This creates a current through the secondary coil

22
Q

What is the equation involving number of turns and voltage

A

Np = Vp

Ns Vs

23
Q

What is the equation for power

A

Power = Voltage x Current

24
Q

What material makes up the core of a transformer

A

Magnetically soft iron

25
Q

What is the National Grid

A

It is the system of distributing electricity from power stations to homes

26
Q

What does a step up transformer do

A

It increases the voltage across a wire

27
Q

What does a step down transformer do

A

It decreases the voltage across a wire

28
Q

What voltage is the grid and super grid

A

132,000 Volts and 400,000 Volts

29
Q

what is the equation for power loss

A

P = Current squared x resistance

30
Q

What are the 3 pins called in a plug

A

earth - green and yellow
Live - Brown
Neutral - Blue

31
Q

What is the earth wire

A

It is a connection between the earth and the metal case of the appliance
If the live wire touches the case the electricity flows through the wire to the earth as it has a low resistance

32
Q

What does the square inside a square symbol represent

A

Double insulated

33
Q

what happens when the current flows through the earth wire

A

The fuse melts from the really high current

34
Q

What do double insulated appliances not have

A

An earth wire as there is no metal in the appliance

Physics (15 decks)

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