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Physics Gcse > ⭐️SP12/SP13-Magnetism, Motor Effect And Electromagnetic Induction > Flashcards

⭐️SP12/SP13-Magnetism, Motor Effect And Electromagnetic Induction Flashcards

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1
Q

What is a permanent magnet?

A

A magnet that’s always magnetic

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2
Q

What is a magnetic field?

A

The space around a magnet where it can attract the materials iron, steel, nickel and colbalt

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3
Q

What is an induced magnet?

A

Where a piece of magnetic material is in a magnetic field and becomes a magnet its self and stops being a magnet when taken out

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4
Q

What can you use to find the shape of a magnetic field?

A

Using plotting compasses

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5
Q

Give examples where magnets are used

A

Electric motors, generators, loudspeakers and things like for latches am life holders

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6
Q

How do plotting compasses work?

A

The needle is a very small magnet and this points to the earths North Pole because the south is attracted to it

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7
Q

Why are compass needles weighted at one end?

A

To keep them level

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8
Q

What is the evidence for the earth’s magnetic field?

A

The behaviour of compasses

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9
Q

What is the earths magnetic field caused by?

A

Electric currents in the molten outer core made of a mixture of iron and nickel

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10
Q

Explain the magnetic field outside a solanoid

A

The field outside is weaker because fields from one side of the coil tend to cancel court fields on the other side of the coil

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11
Q

Explain the magnetic field inside a solenoid

A

The field is very strong because the individual fields add together to form a very strong field

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12
Q

What is an electromagnet?

A

A coil of wire with a current flowing through it

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13
Q

What happens of you put iron in an electromagnet? What does the iron become?

A

You make the magnetic field stronger, the iron becomes a temporary magnet because it’s only magnetic while the field from the electromagnet is affecting it

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14
Q

What is caused when a current flows through a wire?

A

A magnetic field

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15
Q

What does the direction of a magnetic field on a wire carrying a current depend on and what happens of this changes direction?

A

Depends on the direction of current and if this changes direction, so does the direction of magnetic field

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16
Q

What does the strength of a magnetic field around an electrical wire depend on?

A

The size of the current so the higher the current the stronger the field

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17
Q

Where is the magnetic field around a wire strongest?

A

Closer to the wire

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18
Q

What is a solanoid?

A

A coil of wire with a magnetic field around it

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19
Q

What happens when a wire is placed between two magnets?

A

It experiences a force as the current created a magnetic field and this interacts with the magnetic field between the magnets

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20
Q

When is the force a wire carrying current the greatest?

When is the force at 0?

A

When the wire is at right angles to the magnetic field produced by the magnets (as the wire has to be between two magnets to feel the force in the first place
0 when the wire is in the same direction as the magnetic field

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21
Q

What is the motor effect?

A

When a wire carrying a current experiences a force when placed between two magnets

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22
Q

What does the direction of the force in a wire carrying a current between two magnets depend on?

A

The direction of the magnetic field and the current

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23
Q

How can you use Fleming’s left hand rule?

A

To determine the direction if the current in the motor effect so:
The force is the thumb F
Magnetic field is the index finger B
The current is the index finger L

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24
Q

How do you find the force on a conductor carrying current at right angles to the magnetic field? Use units

A

Force (N) = magnetic field strength (N/ Am) or ( Tesla (T)) x current (A) x length (m)
F = B x I x L

25
Q

What causes the rotation in electric motors?

A

The force on a conductor in a magnetic field

26
Q

What are carbon brushes on an electric motor used for?

A

Make electrical contacts between the circuit and motor

27
Q

Describe how an electric motor works

A

There is a force in each part of the wire carrying a current in the magnetic field and so using a coil with many turns of the wire increases the total force turning the coil

28
Q

What does the split ring commutator do?

A

It ensures the force on the coil always turns it in the same direction by making the current is always flowing in the correct direction to make the coil continue to spin

29
Q

What can a changing magnetic field induce?

A

A voltage or potential difference in a wire causing a current to flow

30
Q

How can a potential difference be induced?

A
  • changing magnetic field
  • if a wire is moved in a magnetic field and this wire is often made into a coil so there is more wire in the changing magnetic field
31
Q

What does the size of an induced potential difference depend on?

A
  • the number of turns in a coil of wire
  • the strength of the magnetic field
  • how fast the magnetic field changes or moves past the coil (reversing the direction of this reversed the direction of the induced potential difference)
32
Q

What if a potential difference causes a current to flow when a magnet is moved through a loop of wire?

A

The magnetic field of the current opposes the original change

33
Q

What does a generator consist of?

A

A coil of Wire that is rotated inside a magnetic field and the ends of the coil are connected to slip rings

34
Q

How does a generator work?

A

As the coil of wire turns, a voltage is induced in the wire.

35
Q

In a generator, what are the carbon brushes used for?

A

They maintain electrical contact with an external circuit by pressing on the slip rings

36
Q

What current does a generator produce?

A

An alternating current so it’s often called an alternator

37
Q

What extra component does a generator in a power station and car have?

A

A rotating electromagnet surrounded by coils of wire

38
Q

What is a dynamo? What kind of current does it produce?

A

A generator with a commutator so produces a direct current

39
Q

What does a commutator do?

A

Switches over the connections every half turn of the coil in a dynamo and so producing a form of direct of direct current because it causes the current in the external circuit to flow in the same direction all the time

40
Q

What do microphones do?

A

They convert the pressure variations in sound waves into variations in current in electrical circuits

41
Q

What do loudspeakers do?

A

They convert variations in an electrical current into sound waves

42
Q

Give the steps to how a microphone works

A
  1. Sound waves hit a flexible diaphragm that’s attached to a coil of wire
  2. The coil of wire surrounds one pole of a permanent magnet and is surrounded by the other pole
  3. As the diaphragm moves, a current is generated in the coil
  4. The movement of the coil depends on the properties of the sound wave
43
Q

Give the steps of how a loudspeaker works

A
  1. The diaphragm is replaced with a paper cone
  2. The coil is wrapped around one pole of a permanent magnet so the A.C. signal causes a force on the coil
  3. When the current is reversed, the force acts in the opposite direction
  4. These movements make the cone vibrate creating the variations in pressure that cause sound waves
44
Q

What does a step up transformer do?

A

Increases the voltage and decreases the current at the same time

45
Q

What does a step down transformer do?

A

Makes the voltage lower and the current higher

46
Q

Where in the national grid is energy wasted by heating the most?

A

Along the transmission lines

47
Q

What’s the voltage of electricity that leaves the power station ?

A

25kV

48
Q

Describe the path of electricity along the national grid with the amount of voltage at each point

A
  1. Electricity leaves the power station at 25kV
  2. A step up transformer increases voltage to 400kV where it goes to the transmission lines
  3. A step down transformer reduces the voltage to 33kV or 11kV for factories
  4. Another step down transformer then reduces the 33kV or 11kV electricity down to 230V for homes and offices
49
Q

After leaving the power station, why is the voltage increased at the step up transformers?

A

To reduce the amount of energy wasted by heating in the transmission lines (pylons)

50
Q

What is a transformer made with?

A

Two coils of insulated wire wound onto an iron core. There is no electrical connection between the two coils

51
Q

What are the coils like on a transformer?

A

The primary coil being the first one has less turns than the secondary coil

52
Q

Why do transformers only work with alternating current? (State only what happens in the primary coil)

A

As when the direction of p.d. Changes many times per second, the a.c. In the primary coil creates a continuously changing magnetic field and the iron core of the transformer carries this magnetic field to the secondary coil

53
Q

What happens in the secondary coil of a transformer?

A

The changing magnetic field induces a changing p.d. In the secondary coil and this is greater in the secondary coil if it has more turns than the primary coil

54
Q

What is the potential difference?

A

The energy transferred by each coulomb of charge that flows through a wire

55
Q

How do you calculate the electrical power?

A 
Electrical power (W) = current (A) x p.d.(V) 
Or

Electrical power W = current squared A x resistance in ohms

56
Q

Give the formula for if a transformer is 100% efficient

A

P.d. Across primary coil (V) x current in primary coil (A) = pd across secondary coil (V) x current in secondary coil (A)

57
Q

Why are calculations related to transformers useful?

A

They can help you explain why transmitting power at high voltage is more sufficient

58
Q

What equations do you need with transformer questions

A

Power W = energy transferred J / time S
Electrical power W = current A x pd V
Electrical power W = current squared A x resistance in ohms

Physics Gcse (22 decks)

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