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AQA Physics > Magnetism and electromagnetism > Flashcards

Magnetism and electromagnetism Flashcards

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1
Q

Where are the magnetic forces strongest for a magnet

A

the poles

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2
Q

A permanent magnet produces its own _______

A

magnetic field

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3
Q

What is an induced magnet?

A

a material that becomes a magnet when it’s placed in a magnetic field

it loses magnetism when removed from the magnetic field

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4
Q

Induced magnetism always causes a ________

A

force of attraction

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5
Q

Magnetic field definition

A

the region around a magnet where a force acts on another magnet or/and magnetic material

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6
Q

The force between a magnetic and a magnetic material is _________

A

always one of attraction

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7
Q

What does the force of the magnetic field depend on?

A

the distance of the field from the magnet

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8
Q

What is the direction of the magnetic field lines?

A

North to south pole

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9
Q

How do we know about the Earth magnetic field?

A

A magnetic compass contains a small bar magnet.

The compass needle points in the direction of theEarth’s magnetic field.

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10
Q

What happens when current flows through a conducting wire?

A

a magnetic field is produced around the write

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11
Q

How to increase the strength of a magnetic field?

A
  • increase the amount of current through the wire
  • the decrease the distance from the wire
  • shape the wire into a solenoid
  • add an iron core
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12
Q

Describe the magnetic field lines inside a solenoid?

A

strong and uniform

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13
Q

How can you experiment the effects of “the size of current” and the “distance” from a wire

A

by placing magnetic compass at different points along the wire and turning the power supply on and off

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14
Q

Why does a solenoid increase the magnetic field strength?

A
  • it concentrates a longer piece of wire into a smaller area

- the lopped shape means that the magnetic field lines around the wire are all in the same direction

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15
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

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16
Q

What is the motor effect caused by?

A

the field created by the current interacting with the magnetic field

17
Q

How can the force in the motor effect be increased?

A

increasing :

  • the size of the current
  • the length of conductor in the magnetic field
  • the flux density (density of the field lines around a magnet)
18
Q

What is the formula to find the force of something when you have flux density?

A

F= BIL

Force = magnetic flux density x current x length (of wire within the field)

19
Q

What would happen to the direction of the force, if the direction of the current or magnetic field is reversed?

A

it will reverse

20
Q

How can the direction of the force on the conductor be found?

A

with Flemings left-hand rule

21
Q

What is an electric motor?

A

A coil of wire carrying a current in a magnetic field and rotates

22
Q

Why do electric motors rotate?

A

because the current going up one side of the coil is in the opposite direction to the current coming back down the other side, so one side moves up and the other moves down

23
Q

What do the carbon brushes in electric circuits do?

A

allow the electric current to pass onto the split-ring commutator

24
Q

Why does a coil stop when it reaches 90 degrees (vertical position) if it didn’t have a split-ring commutator?

A

because the current would continue to flow through each side of the coil in the same direction (opposite directions), so the direction of the forces exerted on both sides wouldn’t change.

this means the tip od the coil will be pulled upwards and the bottom downwards so the coil will stop rotating

25
Q

What is a split-ring commutator?

A

a device used to reverse the direction of flow of an electric current in motors and generators

26
Q

How is electric current passed onto the split-ring commutator?

A

the spilt ring is connected to conducting brushes

27
Q

How do coils rotate continuously?

A

each time the coil passes the vertical position, the direction in which current flows around the coil reverses

this reverses the direction of the force exerted on each side of the coil which in turn cause continued rotation in the clockwise rotation

28
Q

How do you make the coil rotate faster?

How do you make the coil turn in the opposite direction?

A

increasing the current or the magnetic field

reversing the current or the magnetic field

29
Q

What do headphones and loudspeakers use the motor effect for?

A

to convert variations in current in electrical circuits to the pressure variations in sound waves

it converts electrical energy into kinetic and sound energy

30
Q

How do you find the direction of field lines?

A

right-hand grip

31
Q

How do you find the north pole of a solenoid

A

right-hand grip:

  • fingers represent the direction of current flow
  • thumb will point to the north pole of the solenoid
32
Q

How do Loudspeakers work?

A

1) when a current flows through the coil, both the coil and the speaker core experience a force due to the magnetic field. The speaker core moves
2) Because the current is alternating when the direction of the current through the coil reverses, so too does the direction of the force exerted on it and the speaker core
3) this causes the speaker core to vibrate back and forth, producing a sound wave
4) the air around the core also vibrates creating variations in pressure that cause a sound wave

33
Q

How do scrapyards work?

A

Scrap vehicles are lifted in a scrap yard using powerful electromagnets attached to cranes

when the current is turned on, the electromagnet attracts magnetic material below it

when the current is turned off, there is no more magnetic force

34
Q

How do circuit breakers work?

A

this is a switch in series with an electromagnet, held by a spring

when the current is too large, the switch is pulled open by the electromagnet and it stays open until it is reset manually

35
Q

How do electric bells work?

A

1) When the switch is pushed, the electromagnet is magnetised
2) The electromagnet attracts the armature
3) The hammer strikes the gong and breaks the circuit
4) the armature springs back, completing the circuit again and remagnetizing the electromagnet
5) the cycle repeats for as long the button remains pushed

36
Q

How do relays work?

A

Relays are used to switch an electrical machine on or off

1) a small current through the coil of the electromagnet magnetises the iron core
2) this pulls the armature onto the electromagnet, whose other end pushes the contacts together, completing the circuit.
3) When the current is switched off, the contacts open again, switching the circuit off.

AQA Physics (22 decks)

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