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Physics > 2.7 Magnetism and Electromagnetism > Flashcards

2.7 Magnetism and Electromagnetism Flashcards

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1
Q

Where are the magnetic forces strongest at?

A

The poles of a magnet

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2
Q

What do two unlike poles do?

A

Attract

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3
Q

What do two like poles do?

A

Repel

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4
Q

Give 2 examples of non-contact forces in Magnetism

A

Attraction and Repulsion

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5
Q

What is a permanent magnet

A permanant magnet…

A

A permanent magnet is a magnet that produces its own magnetic field

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6
Q

What is an induced magnet

A

An induced magnet is a material that becomes a magnet when it is placed in a magnetic field

An example of an induced magnet is iron filings

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7
Q

What happens when an induced magnet is removed from its magnetic field?

A

It loses its magnetism quickly

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8
Q

What type of magnet only causes forces of attraction?

A

Induced Magnets

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9
Q

How can you check if a magnet is permanent?

A

By checking if it repels another magnet

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10
Q

Differences between a permanent and induced magnet

A

Difference 1:
- A permanent magnet is a magnet that produces its own magnetic field
- An induced magnet becomes a magnet when placed in a magnetic field

Difference 2:
- An induced magnet always causes forces of attraction
- A permanent magnet causes forces of attraction as well as repulsion

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11
Q

Which 4 materials are magnetic

A
  • Iron
  • Steel
  • Cobalt
  • Nickel
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12
Q

What is a magnetic field?

A

A magnetic field is the region around a magnet where a non-contact magnetic force acts on another magnet OR a magnetic material

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13
Q

What is the force between a magnet and a magnetic material?

A

Attraction

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14
Q

What factor affects the strength of the magnetic field of a bar magnet

A
  • The distance from the magnet.
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15
Q

Where is the direction of a magnetic field line?

A

The direction of a magnetic field line is from the north (seeking) pole of a magnet to the south(seeking) pole of the magnet

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16
Q

What does a magnetic compass contain?

A

A small bar magnet that points in the direction of the Earth’s magnetic field

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17
Q

How is the behaviour of a magnetic compass related to evidence that the core of the Earth is magnetic

A
  • A magnetic compass contains a small bar magnet.
  • A compass needle always aligns towards the same place on Earth
  • This provides evidence that the Earth’s core must be magnetic
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18
Q

PRACTICAL QUESTION:

Plot the magnetic field of a bar magnet

A
  • Place the bar magnet on a piece of paper
  • Place the compass near the North pole of the magnet
  • Mark the direction the needle points towards
  • Move the compass so that the South pole of the needle touches the point that has just been marked
  • Mark the new point where the needle points towards
  • Repeat this until the South pole has been reached
  • Connect the marks to show the field lines
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19
Q

What happens when current flows through a wire?

A

It creates a magnetic field around the wire

20
Q

How can the direction of the magnetic field in a wire be found?

A

Using the right hand rule

21
Q

How can we increase the strength of a magnetic field around a wire?

A
  • Increase the size of the current
22
Q

What does the direction of the magnetic field of a wire depend on?

A

The direction of the magnetic field of the wire depends on the direction of the current
(right hand rule)

23
Q

What is a solenoid?

A

A solenoid is coil of wire that is coiled into a spiral shape

24
Q

What does a solenoid do?

A

Strengthens the magnetic field produced by a current through a wire

25
Q

How can we increase the strength of the magnetic field around a wire?

A

Shaping a wire to form a solenoid increases the strength of the magnetic field around current in a wire

26
Q

Describe the Magnetic field inside a solenoid

A

The magnetic field inside a solenoid is strong and uniform

27
Q

Describe the Magnetic field outside a solenoid

A

The magnetic field around a solenoid has a similar shape to the magnetic field around a bar magnet

28
Q

What does the direction of the magnetic field of a wire depend on?

A

The direction of the magnetic field depends on the direction of the current in the wire
(Right hand rule)

29
Q

How does a solenoid increase the magnetic effect of current compared to a simple wire?

A

The small magnetic fields caused by the current in each coil add together to make a stronger overall magnetic field that act in the same direction

30
Q

How can we increase the strength of a solenoid

A
  • Increasing the current that flows through the solenoid
  • Increasing the number of turns of wire in the solenoid
  • Adding an iron core to the inside of the solenoid
31
Q

What is an electromagnet?

A

An electromagnet is a solenoid with an iron core inside

32
Q

What is the key difference between a magnet and an electromagnet?

A

An electromagnet can be switched on and off

33
Q

What effect does an iron core have on a solenoid?

Why?

A

It strengthens the solenoid’s magnetic field as the iron inside the solenoid becomes an induced magnet when the solenoid is switched on

34
Q

Fleming’s Left Hand Rule

A
  • Thumb - Force
  • First Finger - Magnetic Field (N to S)
  • Second Finger - Current

FBI

35
Q

What is the motor effect?

A

The motor effect is when a conductor carrying a current (such as a wire) is placed in a magnetic field, and the magnet producing the field and the conductor exert a force on each other

36
Q

What does the wire carrying the current have to be for the motor effect to be the most effective?

A

At right angles to the magnetic field

37
Q

How can the size of the force on the conductor be increased (in a motor effect)

A
  • Increasing the current
  • Using a stronger magnet
38
Q

What is magnetix flux density?

A

Magnetic flux density is a measure of the strength of the magnetic field

39
Q

Formula for the force of a wire carrying current at right angles to a magnetic field?

A

F = B I L
force = magnetic flux density × current × length

Force in N
B in T (Tesla)
Current in Amps
Length in m

40
Q

How does an electric motor work?

A
  1. When a coil of wire that carries a current is placed at right angles inside a magnetic field, it exerts a force where one side of the coil moves up and the other moves down (As we can see using Fleming’s left hand rule)
  2. This causes the coil to rotate in a clockwise or anticlockwise movement until the loop of wire is now rotated 90 degrees.
  3. At this point, there is no connection to the battery because of the gap in the split-ring commutator
  4. The coil of wire has momentum, so it keeps on moving
  5. The split-ring commutator, which is a metal ring, swaps the connections with the battery through the small graphite brushes (which allow electric current to pass through the ring)
  6. This allowsthe motor to keep rotating in the same direction.
41
Q

What is the function of the split ring commutator?

A

The split ring commutator keeps the motor rotating in the same direction by allowing the current in the coil to change direction each half-turn as the coil rotates.

42
Q

How do loudspeakers and headphones work?

A

Loudspeakers and headphones use the motor effect to convert variations in current in electrical circuits to the pressure variations in sound waves.

43
Q

Explain how loudspeakers work

NOT FINISHED

A
  1. A loudspeaker consists of a coil of wire which is wrapped around one pole of a permanent magnet
  2. An alternating current passes through the coil of the loudspeaker. This creates a changing magnetic field around the coil
  3. As the current is constantly changing direction, the direction of the magnetic field will be constantly changing
  4. The magnetic field produced around the coil interacts with the field from the permanent magnet
  5. This produces a resultant force, causing the coil/cone to move
  6. The force exerted on the coil is constantly changing as the magnetic field is constantly changing
  7. This causes the coil to osciallate, producing sound waves
44
Q

How can a potential difference be induced across the ends of a conductor (e.g. a wire)?

A

A potential difference be induced across the ends of an electrical conductor when:
- it cuts through the magnetic field, moving relative to it
- there is a changing magnetic field around the wire

45
Q

What is the generator effect?

A
  • The generator effect is when a potential difference is induced across the ends of a conductor (e.g. wire)
  • When the conductor is part of a complete circuit, the induced potential difference makes an electric current pass around the circuit

Physics (10 decks)

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