Topic 7: Electromagnetism Flashcards

1
Q

Describe the direction of magnetic fields in a magnet

A

Out from the north, in through the south

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2
Q

Where is the magnetic field in a magnet most strongest?

A

The poles

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3
Q

What do magnets do?

A

Attraction and repulsion

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4
Q

How do you change the size of the induced potential difference?

A
  • change the strength of the magnetic field - larger potential difference
  • move the wire or magnets more quickly - bigger potential difference
  • shape the wire into a coil - bigger potential difference
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5
Q

Describe the generator effect (electromagnetic induction)

A
  • magnetic field around a permanent magnet
  • wire moves within the magnetic field
  • induces p.d in the wire, which results in an alternating current
  • this wire has to be part of a complete circuit
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6
Q

What is an alternator?

A

A coil of wire rotating in a magnetic field

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7
Q

Describe how alternators generate an alternating current

A
  • the coil moves through the magnetic field
  • a potential difference is induced (across the coil)
  • there is a complete circuit, so a current is induced (in the coil)
  • every half turn, the potential difference reverses direction
  • so every half turn the current changes direction
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8
Q

Describe how a sound wave is produced in loud speakers and microphones

A
  • the current creates a magnetic field (around the coil)
  • (which) interacts with the permanent magnetic field
  • producing a (resultant) force causing the coil/ cone to move
  • (when the) direction of the current (AC) reverses, the direction of the (resultant) force reverses, producing a sound wave
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9
Q

Describe how in both transformers of the National Grid, how an alternating current is caused

A
  • an alternating current in primary coil
  • induces an alternating magnetic field in the core
  • induces an alternating p.d. in secondary coil
  • causing an alternating current, if it is a complete circuit
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10
Q

Describe how sound waves are produced in a loud speaker

A
  • the alternating current creates a magnetic field around the cone
  • which interacts with the magnetic field in permanent magnet
  • this generates force on the cone - causing it to vibrate
  • when the direction of the alternating current reverses, the direction of the resultant force reverses producing a sound wave
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11
Q

Describe how dynamos generate direct current

A

Dynamos work in the same way as alternators, apart from one important difference
They have a split-ring commutator instead of slip rings
This swaps the connection every half turn to keep the current flowing in the same direction

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12
Q

Describe how a solenoid can increase the strength of the magnetic field that the wire produces

A
  • you can increase the strength of the magnetic field that the wire produces by wrapping the wire into a coil called a solenoid
  • this happens because the field lines around each loop of wire line up with each other
  • this results in lots of field lines pointing in the same direction that are very close to each other
  • the magnetic field inside a solenoid is strong and uniform
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13
Q

Explain why when there’s a current in the coil, the coil rotates continuously

A
  • the sides of the coil experience a force in opposite directions
  • the forces cause moments that act in the same direction
  • the carbon brush rotates as the force acts on it
  • the split-ring commutator swaps the contacts every half turn to keep the motor rotating in the same direction
  • the commutator reverses the current
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