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Physics > P15- Electromagnetism > Flashcards

P15- Electromagnetism Flashcards

1
Q

Rule of attraction of the poles?

A

Like poles repel
Opposite poles attract

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2
Q

3 magnetic metals?

A

Iron, cobalt, nickel

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3
Q

Magnetic field def?

A

Region around a magnet

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4
Q

Where do magnetic compasses always point and why?

A

North as Earth’s core is magnetic

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5
Q

Magnetic field lines on a bar magnet?
Which direction do they travel?

A

Travel from north to south, closer together at poles

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6
Q

Distance from magnet affecting strength of magnetic field?

A

Greater distance, weaker magnetic field

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7
Q

What is induced magnetism?

A

Magnetism created in an unmagnetised magnetic material by placing it in a magnetic field

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8
Q

Why is steel used in permanent magnets instead of iron?

A

Steel doesn’t lose its magnetism easily, iron does

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9
Q

Solenoid def?
Why is it helpful?
Why is it better?

A

Long coil of insulated wire
Produces a magnetic field when current is passed through the wire
Stronger field than if straight

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10
Q

Increased current affecting a solenoid’s magnetic field?
Reversed current affecting a solenoid’s magnetic field?

A

Increased current= increased strength of field
Reversed current= direction reversed

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11
Q

Magnetic field lines around a solenoid look like?
Key fact?

A

Like a bar magnet but each line is a complete loop as it passes through the solenoid

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12
Q

Magnetic field lines inside a solenoid are all..? (2 things)

A

Parallel and in the same direction

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13
Q

Magnetic field lines around a wire look like..?

A

Circles around a wire in a bullseye shape

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14
Q

Electromagnet

A

Solenoid that creates a magnetic field created when current passes through, can be turned on and off

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15
Q

4 uses for an electromagnet

A

Scrapyard cranes, circuit breakers, electric bells, relays

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16
Q

How does an electric bell work?

A

Current flows through electromagnet, creating magnetic field. This attracts the iron armature, causing the hammer to strike and ring the gong. This opens another switch and breaks the circuit. The electromagnet is switched off and loses its magnetic field so the hammer springs back into its original position and the process repeats.

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17
Q

How does a circuit breaker work?

A

When too much current passes through the coil the electromagnet becomes magnetised and attracts the switch. This opens the switch, breaks the circuit and needs to be reset manually.

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18
Q

How does a relay work?
And what does it do?

A

Current through the electromagnet attracts armature. This closes the switch gap, switches on the machine. Smaller current is used to switch on a machine with a larger current

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19
Q

How does a scrapyard crane work?

A

Strong electromagnets are attached to cranes, attracts steel frame of vehicles when its on. When off the vehicle frame falls off the electromagnet.

20
Q

Motor effect def?

A

A force acting on a wire in a magnetic field when current passes through the wire.

21
Q

How to increase the size of the force in the motor effect?

A

Increased current
Stronger magnet

22
Q

What does the size of the force in the motor effect depend on?
When is the force greatest?
When is the force zero?

A

The angle between the wire and magnetic field lines
When wire is perpendicular to magnetic field lines
When wire is parallel to magnetic field lines

23
Q

How does Fleming’s left hand rule work?

A

Palm facing me
First finger= magnetic field from N to S
Second finger= current
Thumb= direction of force

24
Q

Magnetic flux density def? and unit?

A

Measure of the strength of a magnetic field (Tesla, T)

25
Why does the coil spin in an electric motor?
A force acts on each side of the coil due to the motor effect The forces are in opposite directions
26
Generator effect def?
When motion between a conductor and a magnetic field creates current, ie a magnet is moved into a coil of wire
27
Electromagnetic induction def?
A potential difference being induced in a conductor (a wire) when it crosses magnetic field lines
28
Why is a current produced when moving a magnet into a coil?
Movement of the magnet induces a potential difference in the coil This causes a current as the coil is part of a complete circuit
29
How to make the current and pd greater in the generator effect? Reverse direction?
Stronger magnet, faster movement, tighter coil Pulling magnet in opposite direction from coil
30
What effect does the generator effect have on the original magnet? How does this create current?
It creates a magnetic field which opposes the original magnet. The magnets repel, work is done by the person moving the magnet, so current is generated
31
Alternator def?
An alternating-current generator with a coil spinning in a magnetic field with two slip-rings
32
Why does an alternator produce alternating current?
The coil passes through the magnetic field creating current, then doesn't pass through magnetic field, stopping the current. As this happens the direction changes as each side is connected to a different ring.
33
Commutator job?
To allow current to pass out of the coil in the generator effect
34
What does the display of an oscilloscope look like of an a.c generator? When is it at its peak? When is it at 0?
When the sides of the coil cross directly through magnetic field lines When the sides of the coil are not touching the magnetic field lines
35
How to increase the size of alternating current produced by the generator effect? Increasing the speed of rotation of the coil does...?
Stronger magnet, more turns in the coil Increases the size and frequency of alternating current
36
Dynamo def?
A direct current generator with a split-ring commutator
37
Why does a dynamo produce direct current?
The coil passes through the magnetic field creating current, then doesn't pass through magnetic field, stopping the current. As this happens the direction stays the same as each side is connected to a opposite sides of one ring.
38
What does the display of an oscilloscope look like of a dynamo? When is it at its peak? When is it at 0? What do two peaks represent?
When the sides of the coil cross directly through magnetic field lines When the sides of the coil are not touching the magnetic field lines Two peaks is one full cycle
39
How does a moving coil microphone work?
Pressure from sound waves cause the diaphragm to vibrate, so the coil vibrates too, causing it to move perpendicular to the magnetic field so a pd is induced. As it is a complete circuit, current is induced which is the same frequency as the sound waves.
40
How does a moving coil loudspeaker work?
Coil is in a magnetic field, motor effect on the current in the coil creates a force. The supplied alternating current changes direction, changing the direction of the force. The cone vibrates in and out due to this change of force , causing sound waves at the same frequency of the alternating pd.
41
What are transformers used for? What happens to one based on the other? How do transformers do this?
Changing the current and potential difference They lower one and increase the other Use electromagnetic induction
42
Step-up transformer effect on pd & current? Step-down transformer effect on pd & current?
Increase pd, decrease current Decrease pd, increase current
43
How do transformers work (detailed) and what do they look like?
-Alternating current passes through primary coil, induces an alternating magnetic field in iron core -Magnetic field lines pass through secondary coil -Magnetic field in secondary coil induces an alternating pd across the secondary coil -If secondary coil is connected in a complete circuit, an alternating current will be produced
44
Why does a transformer only work with a.c?
A changing magnetic field is required to induce a.c in the secondary coil
45
Difference between a step-up or step-down transformer and why?
A step-up has more turns in the secondary coil so the pd is increased and the current is decreased
46
Key fact about transformer efficiency?
They are very efficient so they are assumed to have 100% efficiency
47
Why is the potential difference increased in the national grid?
To reduce the current so less heating effect takes place, so less energy is transferred to the surroundings

Physics (18 decks)

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