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Physics > Topic 7: Magnetism and Electromagnetism > Flashcards

Topic 7: Magnetism and Electromagnetism Flashcards

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1
Q

What do two unlike poles do?

A

Attract each other

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2
Q

What do two like poles do?

A

Repel each other

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3
Q

What is a permanent magnet?

A

A magnet 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 are 2 rules of induced magnets?

A
  1. Always cause a force of attraction
  2. Loses its magnetism quickly when removed from a magnetic field
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6
Q

Which way do field lines go?

A

From north to south

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7
Q

How can you plot a magnetic field pattern using a compass? [4]

A
  1. Inside a compass is a tiny bar magnet
  2. North pole of this magnet is attracted to the south pole of any other magnet
  3. So the compass points in the direction of the magnetic field it is in
  4. You can move a compass around a magnet and trace its position to plot a magnetic field pattern
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8
Q

How does the behaviour of a magnetic compass show that the core of the Earth must be magnetic?

A

When not near a magnet, compasses always point north

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9
Q

What happens when a current flows through a wire?

A

A magnetic field is created

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10
Q

What does shaping a wire to form a solenoid do?

A

Increases the strength of the magnetic field

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11
Q

How can you increase the strength of an electromagnet?

A
  1. Increase the current
  2. Add an iron core
  3. Increase the number of turns of the solenoid (whilst keeping the length of wire the same)
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12
Q

When does the motor effect occur?

A

When a current-carrying wire is placed in a magnetic field

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13
Q

How does the wire have to be orientated to feel the full force in the magnetic field?

A

At 90° to the magnetic field

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14
Q

In Fleming’s left-hand rule, what does your first finger represent?

A

Direction of field (magentic field)

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15
Q

In Fleming’s left-hand rule, what does your second finger represent?

A

Direction of current

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16
Q

In Fleming’s left-hand rule, what does your thumb represent?

A

Direction of motion (force)

17
Q

Explain how a motor turns in terms of forces

A

One side of the coil acts up and one acts down and because the coil is on a spindle it rotates

18
Q

Explain how a split-ring commutator makes an electric motor spin [4]

A
  1. It swaps the positive and negative connections every half turn
  2. This swaps the direction of the current every half turn
  3. Therefore, the forces acting on the coil will always be in the same direction
  4. The coil will rotate in the same direction and spin
19
Q

How can the speed of a motor be increased? [3]

A
  1. Increasing the current
  2. Adding more turns to the coil
  3. Using stronger magnets
20
Q

State the ‘generator effect’

A

The induction of a potential difference in a wire which is moving relative to a magnetic field, or experiencing a change in magnetic field

21
Q

How can you increase the strength of the induced current in a generator? [3]

A
  1. Increase strength of magnetic field
  2. Increase speed wire is moved at
  3. Add more turns to coil
22
Q

Describe how dynamos work [4]

A
  1. A coil of wire is turned inside of a magnet
  2. This induces a magnetic field and a current in the coil of the wire
  3. The split-ring commutator switches the connections every half turn
  4. This causes the current to be a direct current
23
Q

What type of current do dynamos produce?

A

Direct current

24
Q

Describe how alternators work [4]

A
  1. A coil of wire is turned inside of a magnet
  2. This induces a magentic field and a current in the coil of the wire
  3. The slip rings and brushes mean that the connections don’t change every half turn
  4. This causes the current to be an alternating current
25
Q

What type of current do alternators produce?

A

Alternating current

26
Q

Explain how loudspeakers work? [6]

A
  1. An alternating current flows through wire and creates a magnetic field in the coil
  2. The magnetic field of the coil interacts with the magnetic field of the permanent magnet
  3. The interacting magnetic fields will exert a force on the coil, causing it to move back and forth along the magnet
  4. This causes the cone to change shape
  5. As the current is alternating, its magnetic field and force it experiences will also alternate. This means that the coil of wire and cone rapidly move back and forth, meaning they vibrate
  6. These vibrations are so fast that they cause pressure variations in the air - which are sound waves
27
Q

Explain how microphones work? [4]

A
  1. Sound waves hit the diaphragm
  2. This causes the diaphragm and coil of wire to move
  3. As the wire is moving within the magnetic field of the permanent magnet, it will generate a current
  4. The frequency and amplitude of the sound waves will determine how much the diaphragm vibrates, and therefore determine the frequency and amplitude of the current
28
Q

What do transformers do?

A

Step-up and step-down the p.d

29
Q

How do step-up transformers increase the p.d (number of coils)?

A

They have more turns on the secondary coil than the primary coil

30
Q

How do step-down transformers decrease the p.d (number of coils)?

A

They have more turns on the primary coil than the secondary coil

31
Q

Explain how a transformer works [5]

A
  1. An alternating p.d is applied across the primary coil
  2. This causes a current to flow and generates a magnetic field
  3. This alternating current then induces an alternating magnetic field in the iron core
  4. This induces a p.d across the secondary coil
  5. This causes a current to flow
32
Q

Why is iron used in transformers?

A

It is easily magnetised

33
Q

What technique is used to determine the direction of the field lines in a wire?

A

Right hand rule

34
Q

In an electromagnet, what happens to the magnetic field when the current is turned off?

A

Magnetic field dissapears

35
Q

What effect do loudspeakers use?

A

Motor effect

36
Q

What effect do microphones use?

A

Generator effect

37
Q

What type of current do loudspeakers and microphones create?

A

Alternating current

Physics (8 decks)

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