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physics > Topic 6: Magnetism and Electromagnetism > Flashcards

Topic 6: Magnetism and Electromagnetism Flashcards

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1
Q

What does a current carrying wire create?

A

magnetic field

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2
Q

The larger the electric current…

A

the stronger the magnetic field

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3
Q

What is the magnetic field around a current carrying straight wire?

A

concentric circles - with wire in the centre (right hand rule)

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4
Q

What is the magnetic field like in the centre of a solenoid?

A

strong and uniform

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5
Q

What is the motor effect?

A

when a current carrying wire is put between magnetic poles and the 2 magnetic fields effect one another - results in a force on the wire causing wire to move

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6
Q

Why do wires experience a force when moving through magnetic field?

A

electrons in current (charged particles) are not moving parallel to the field lines

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7
Q

Motor effect: strength of force increases…

A

strength of magnetic field

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8
Q

Motor effect: as current increases…

A

force increases

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9
Q

Motor effect: Reversing the current or magnetic field does what to the force?

A

reverses the direction of the force

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10
Q

Why is iron used in transformers?

A

as it is magnetically soft - can demagnetise 50 times a second

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11
Q

Motor effect: what angle does the wire have to be at to experience a full force?

A

90 degrees

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12
Q

Fleming’s left hand rule: what does the thumb represent?

A

direction of force

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13
Q

Fleming’s left hand rule: what does the first finger represent?

A

direction of magnetic field

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14
Q

Fleming’s left hand rule: what does the middle finger represent?

A

direction of current

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15
Q

What does a split ring commutator do?

A

swaps direction of current every half turn of motor, to keep motor going in same direction

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16
Q

2 ways to reverse direction of motor

A
  1. swap magnetic poles over
  2. swap polarity of d.c. supply
17
Q

4 ways to increase speed of motor

A
  1. increase current
  2. increase no. turns of coil
  3. increase magnetic field strength
  4. add soft iron core
18
Q

Loudspeakers work because of the…

A

Motor Effect

19
Q

Loudspeakers: 1. what type of signals are fed to the coil of wire in the speaker?

A

a.c. electrical signals - from an amplifier

20
Q

Loudspeakers: 2. as the coil is surrounded by a permanent magnet a force is…

A

exerted on the coil - making it move back and forwards

21
Q

Loudspeakers: 3. the coil moving back and forwards makes…

A

the cone vibrate and create sounds

22
Q

What is electromagnetic induction?

A

creation of a voltage in a wire which is experiencing a change in magnetic field

23
Q

What is the Dynamo effect?

A

using electromagnetic induction to generate electricity from kinetic energy

24
Q

2 situations in which EM induction is achieved

A
  1. electrical conductor moves through a magnetic field
  2. the magnetic field through an electrical conductor changes (bigger or smaller or reverses)
25
Q

If the direction of a conductor through a magnetic field is reversed, then the induced voltage/ current will be…

A

reversed too

26
Q

3 ways to increase the voltage from electromagnetic induction

A
  1. increase strength of magnet
  2. increase no. turns of coil
  3. increase speed of movement
27
Q

How does a generator work?

A
  1. rotate a coil in a magnetic field
  2. as coil spins, current is induced in coil
  3. current changes direction every half turn
  4. slip rings and brushes means that the current doesn’t swap direction every half turn
  5. produces AC voltage
28
Q

What do transformers do?

A

change the size of the voltage of an alternating current

29
Q

What is a transformer made up of?

A

primary and secondary coil - joined with an iron core

30
Q

How do step-up transformers work?

A

increase the voltage - more turns on secondary coil than primary coil

31
Q

How do step-down transformers work?

A

decrease the voltage - more turns on primary coil than secondary coil

32
Q

How is a step-up transformer used in transmitting mains electricity?

A

boost voltage before it is transmitted (after power station)

33
Q

How is a step-down transformer used in transmitting mains electricity?

A

used at end of journey - reduce voltage so it is safer for domestic use (reduced to about 230V)

physics (10 decks)

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