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Physics > Electromagnets > Flashcards

Electromagnets Flashcards

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1
Q

Which metals are magnetic?

A
  • Iron
  • Cobalt
  • Nickel
  • Steel
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2
Q

Which direction do magnetic field lined flow in?

A

From north to south.

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3
Q

What is a permanent magnet?

A

A material that produces its own magnetic field.

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4
Q

What is an induced magnet?

A

A material that becomes a magnet when placed in a magnetic field.

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5
Q

What causes the Earth’s magnetic field?

A

The molten iron outer core.

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6
Q

Why do compasses point to the north pole?

A

It is the magnetic south pole.

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7
Q

What is a magnetic field?

A

The area around a magnet where a force will be exerted on another magnet/magnetic material.

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8
Q

Which end is the south pole of a solenoid?

A

The end where the current flows clockwise.

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9
Q

Which end is the north pole of a solenoid?

A

The end where the current flows anti-clockwise.

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10
Q

How can the strength of a solenoid by increased?

A
  • Increasing the number of turns
  • Increasing the current
  • Adding an iron core
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11
Q

What is Fleming’s left hand rule?

A

Thumb: Motion
First finger: Magnetic field
Second finger: Current

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12
Q

How can the force on a wire in a magnetic field be increased?

A
  • Increasing the current
  • Increasing the magnetic flux density
  • Increasing the length of wire in the magnetic field
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13
Q

What happens if current flows through a wire in the same direction as the magnetic field?

A

The force on the wire is 0N

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14
Q

What is the motor effect?

A

Force acting on a wire placed in a magnetic field when current flows through it.

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15
Q

Why is a split ring commutator used in a DC motor?

A

It reverses the direction of the current every half turn so the coil experiences a force in the same direction, despite each side cutting through the magnetic field line in the opposite direction.

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16
Q

Why does the motor continue spinning even though the brushes disconnect every half turn?

A

Its momentum keeps it spinning until the brushes reconnect.

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17
Q

Why does the coil of a motor spin?

A
  • The current in the coil creates a magnetic field
  • This interacts with the permanent magnet
  • The current flows in opposite directions on the two sides of the coil
  • The forces act in opposite directions, making it spin.
18
Q

How does a loudspeaker work?

A
  • AC current in coil reverses poles of solinoid
  • Interaction between magnetic fields causes vibrations in the cone
  • This moves air molecules, creating the pressure variations needed for sound waves.
19
Q

What is electromagnetic induction?

A

Potential difference induced in a conductor when it cuts through magnetic field lines, causing current to flow.

20
Q

Why do you have to do work when moving a magnet through a coil of wire?

A
  • The polarity of the solenoid will change to oppose the movement
  • Energy used is transferred along the coil of wire
21
Q

When moving a bar magnet in a coil of wire to induce a potential difference, how do you create a higher potential difference?

A

Moving the magnet faster.

22
Q

What is an alternator?

A

An AC generator.

23
Q

How can an induced current be increased?

A
  • Increasing the speed of the coils rotation
  • Increasing the strength of the magnetic field
  • Increasing the number of turns in the coil
  • Increasing the total area of the coil
24
Q

What is a dynamo?

A

A DC generator.

25
Q

Why are slip rings and brushes used in an AC generator?

A
  • They ensure that the wires do not get tangled
  • The brushes are an electrical contact
26
Q

What happens if a DC generator is rotated twice as fast?

A
  • The frequency is doubled
  • The amplitude is doubled
27
Q

Why are electromagnets used instead of permanent magnets for a scrapyard crane?

A

They can be turned off to drop objects.

28
Q

How does a circuit breaker work?

A
  • Push switch is held in place iron bolt
  • Electromagnet is put into the circuit next to the bolt
  • When the current gets too high, the magnet pulls out the bolt
29
Q

How does an electric bell work?

A
  • Electromagnet attracts metal arm
  • Arm hits the gong and breaks the circuit connection
  • This switches off the electromagnet
  • Arm moves back
  • The circuit is completed again
30
Q

What is a relay switch?

A
  • An electromagnetic switch
  • Allows a small circuit to turn on/off a much larger circuit.
31
Q

What are the 2 ways a relay switch can be used?

A
  • A switch
  • An amplifyer
32
Q

How does a relay switch work?

A
  • It has a coil of wire which becomes a temporary magnet
  • This attracts a switch for a larger circuit, turning it on/off
33
Q

How does a microphone work?

A
  • Sound waves move diaphragm
  • Diaphragm moves a coil, making it cut through magnetic field lines
  • This induces a potential difference in the coil
  • Electrical signal matches the sound waves
34
Q

How does a transformer work?

A
  • AC in primary coil induces a changing magnetic field in the core
  • Secondary coil cuts through changing fie;d lines, so alternating potential difference is induced
  • Number of turns on each side determines the voltage output
35
Q

What does a step up transformer do?

A

Increases voltage and decreases current.

36
Q

What does a step down transformer do?

A

Decreases voltage and increases current.

37
Q

Which side is the primary coil on a step up transformer?

A

The coil with less turns on it.

38
Q

Which side is the primary coil on a step down transformer?

A

The coil with more tuns on it.

39
Q

What are the 2 uses of transformers?

A
  • Increasing efficiency in power transmission
  • Changing mains voltage for different devices
40
Q

What are transformer cores made from?

A

Iron.

Physics (8 decks)

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