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GCSE PHYSICS PAPER 2 > P7 > Flashcards

P7 Flashcards

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1
Q

Where are the magnetic forces strongest on a magnet?

A

At the poles

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2
Q

Attraction and repulsion between two magnetic poles are examples of what kind of force?

A

Non-contact

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3
Q

What is a permanent magnet?

A

A magnet which produces its own magnetic field

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4
Q

What is an induced magnet?

A

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

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5
Q

How can you demagnetise a permanent magnet?

A

By applying force or heating the magnet as this disorganises the particles

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6
Q

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

A

It loses all/most of its magnetism quickly

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7
Q

What is the magnetic field?

A

The region around a magnet where a force acts on another magnet or on a magnetic material

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8
Q

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

A

one of attraction

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9
Q

What does the strength of the magnet depend on?

A

The distance from the magnet

(the field is strongest at the poles)

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10
Q

In which direction does the magnetic field always go?

A

From North to South

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11
Q

How did explorers navigate the Earth using magnetic fields?

A
  • In magnetic compasses there are small bar magnets
  • The Earth has a magnetic field and the compass needle points in the direction of the Earth’s magnetic field
  • The north of the compass points to the North Pole (Earth’s magnetic South)
  • The south of the compass points to the South Pole (Earth’s magnetic North)
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12
Q

How can you check the direction of the magnetic field?

A
  • right hand
  • thumbs up pointing in the same direction as the current
  • the way your other fingers wrap around (knuckle to tip) is the direction of the magnetic field.
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13
Q

What does the strength of this magnetic field rely on?

A
  • the distance from the wire
  • the current through the wire
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14
Q

What is a solenoid?

A

A coil of current carrying wire

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15
Q

What happens when a current flows through a wire?

A

A magnetic field is produced perpendicular to the wire in concentric circles around it

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16
Q

How does shaping a wire to form a solenoid increase the strength of the magnetic field?

A

The field lines around each loop of wire line up with each other and form a stronger magnetic field. The magnetic field is strongest and uniform through the middle of the solenoid

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17
Q

How can you further increase the strength of the magnetic field of a solenoid?

A

By adding an iron core

18
Q

What is an electromagnet?

A

A solenoid with an iron core

19
Q

What is the motor effect?

A

When a conductor carrying a current is placed in a magnetic field, the magnet producing the field and the conductor exert a force on each other

20
Q

How must the wire be positioned to experience the full force?

A

At 90 degrees to the field (perpendicular)

21
Q

What is Fleming’s left hand rule used for?

A

To determine the direction of the force

  • First Finger= magnetic Field
  • second finger= Current
  • thumb = motion (direction of the Force)
22
Q

What does the force on a conductor in a magnetic field depend on?

A
  • The magnetic flux density measured in tesla (T)
  • The current (amps)
  • The length of the wire in metres
23
Q

What is the equation used to calculate force?

A
  • F= B x I x lF= force (N)B= magnetic flux density (T)I= current (A)l= length (m)
24
Q

What is the basis of an electric motor?

A

A coil of wire carrying a current in a magnetic field tends to rotate.

25
Q

How does a motor work?

A
  • The power supply applies a potential difference across the coil
  • A current flows through the coil
  • A magnetic field is created around the coil
  • The magnetic field interacts with the magnetic field of the permanent magnet
  • This creates a force that makes the coil spin
  • Every half-turn, the direction is reversed by a split-ring commutator
26
Q

What is the function of a split-ring commutator?

A

A split-ring commutator reverses the direction of the current in the wire every half-turn

  • it connects to the circuit with electrical contacts called brushes
27
Q

How can you increase the speed of a motor?

A
  • increase the current
  • increase the strength of the magnetic field
  • increase the number of coils
28
Q

Why do loudspeakers/headphones vibrate when AC current flows through the coil?

A
  • the current flowing through the coil creates a magnetic field
  • this interacts with the permanent magnetic field and produces a resultant force
  • When the direction of the current changes, the direction of the force changes to the opposite direction
  • This causes vibrations in the cone which produce pressure changes in the air to produce sound
29
Q

What is the generator effect?

A

If an electrical conductor moves relative to a magnetic field or if there is a change in the magnetic field around a conductor a potential difference is induced (and current if there’s a complete circuit) across the ends of the conductor

30
Q

How does induced current work?

A

An induced current generates a magnetic field that opposes the original change

(either the movement of the conductor or the change in magnetic field)

31
Q

Explain how alternators work

A
  • generates AC (alternating current)
  • As the coil spins, a current is induced in the coil
  • every half-turn, the current changes direction
32
Q

Explain how dynamos work

A
  • generates DC (direct current)
  • They use a split-ring commutator as their electrical contact
  • This swaps the connection every half-turn to keep current flowing in the same direction
33
Q

What do microphones use the generator effect to do?

A

To convert the pressure variations in sound waves into variation in current in electrical circuits

(converts sound waves into electrical signals)

34
Q

How does a moving-coil microphone work?

A
  • the sound waves cause the diaphragm to oscillate
  • This causes the cone to vibrate which interacts with the permanent magnetic field (it moves through)
  • As a result, a potential difference is induced
35
Q

What is a transformer?

A

A device that changes the potential difference of a device, using the generator effect

36
Q

How is the effect of an alternating current in one coil in inducing current in another used in transformers?

A
  • The current flowing through a primary coil causes a magnetic field
  • this creates an induced magnetic field in the iron
  • an AC causes the induced magnetic field to also alternate
  • the constantly changing magnetic field cuts through the secondary coil
  • this induces an alternating potential difference in the secondary coil (due to the generator effect)
  • if the secondary coil is part of a complete circuit a current will flow with some frequency of AC in the primary coil
37
Q

Why are iron cores used?

A

Iron is easily magnetised

38
Q

What does the ratio of potential differences across the primary and secondary of coils of a transformer depend on?

A

The number of turns on each coil

Vp/Vs = np/ns

Vp/Vs= potential difference (primary and secondary)

np/ns= number of turns on each coil (primary and secondary)

39
Q

How can you manipulate the amount of potential difference induced?

A

by varying the number of coils wrapped around

40
Q

How does potential difference and the number coils differ in step up and step down transformers?

A

step-up: higher potential difference in the secondary coil, more turns on the secondary coil
- increases V

step-down: higher potential difference in the primary coil, more turns on the primary coil
- decreases V

41
Q

What would happen if transformers were 100% efficient?

A

the electrical power input and output would be equal

GCSE PHYSICS PAPER 2 (4 decks)

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