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Physics > P15 : Magnetism > Flashcards

P15 : Magnetism Flashcards

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1
Q

what are permanent magnets?

A

produce its own magnetic field ( doesnt lose magnetism)

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2
Q

what is an induced magnet?

A

when a magnetic material is placed in a magnetic field
- temporarily magnetic

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3
Q

magnetic field?

A

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

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4
Q

how are magnetic fields drawn?

A
  • from north to south
  • lines spaced out -> weaker attraction
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5
Q

what is the geographical north/south pole?

A

geographic north pole - magnetic south pole
geographic south pole - magnetic north pole

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6
Q

what is a solenoid/ how does it increase magnetic effect ?

A

long current-carrying coil used to generate a uniform magnetic field within its core
- coiling wire causes field to align/ form giant single field

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7
Q

how is the strength of magnetic field around solenoid increased?

A
  • increase size of current
  • increase no. coils
  • adding iron core through centre of coils
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8
Q

how does iron core increase magnetic strength?

A
  • easier for magnetic field lines to pass through air
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9
Q

what are electromagnets?

A

solenoids with an iron core

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10
Q

how can magnetic field of electromagnet be swicthed on/off?

A

On : - CURRENT FLOWS
off - no current flows

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11
Q

motor effect?

A

A wire with current flowing through it is placed in a magnetic field and experiences a force
- if wire is 90 degrees to magnetic field - experiences force
- if wire is parallel to magnetic field- no force

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12
Q

factors affecting force exerted in motor effect?

A
  • increasing current in wire - increase magnetic field around wire
  • use stronger magnets - increase field between 2 poles
  • place wire at 90 degrees to magnetic field
  • increase no. turns in coil
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13
Q

how to determine direction of force (thrust) on current carrying wire ?

A

Fleming’s left hand Rule
thumb - thrust
first finger - field
second finger - current

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14
Q

what is the right hand thumb rule?

A
  • used to work out direction of magnetic field
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15
Q

how do electric motors rotate?

A
  • current flows 90 degrees to direction of magnetic field –> magnetic field created around coil
  • magnetic field from coil and from magnets interact
  • results in force exerted on coil
  • as current will flow in opposite directions in each side of coil, the force will move one side of coil up/down –> rotation until in vertical position (forces act up and down)
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16
Q

how to increase speed of rotation of coil D.C motors?

A

increasing current/stronger magnet

17
Q

how is direction of rotation of coil changed?

A
  • reverse direction of current
  • reversing direction of magnetic field by reversing poles
18
Q

what does a loudspeaker consist of?

A

a coil of wire wrapped around one pole of permanent magnet

19
Q

what makes the coil oscillate in loudspeakers?

A
  • an alternating current passes through the coil in loudspeaker
  • creates changing magnetic field - current is constantly changing direction, so magnetic field is too
  • magnetic field produced around coil interacts with field around magnet - exert force on coil
  • as magnetic field direction is changing , force exerted on coil changes direction - makes coil oscillate
20
Q

what is the generator effect?

A

When there is a relative movement between a conductor and a magnetic field/magnetic field changes a potential difference is induced across the conductor.

21
Q

what happens when a wire (conductor) is put into a fixed magnetic field?

A

wire cuts through field lines
- induced Potential difference on wire

22
Q

factors effecting induced potential difference?

A
  1. speed at which wire,coil or magnet moves
    - increase speed - increase rate at which magnetic field lines are cut–> MORE PD
  2. no. turns on the coils in wire
    - more coils means more mganetic field lines cut –> MORE PD
  3. size of coil
  4. strength of magnetic field
  5. orientation of poles on magnet - effects direction of pd
23
Q

what is Lenz’s law?

A

The direction of an induced potential difference always opposes the change that produces it
- This means that any magnetic field created by the potential difference will act so that it tries to stop the wire or magnet from moving

24
Q

uses of generator effect?

A
  • generate AC in ALTERNATOR
  • generate DC in DYNAMO
25
Q

When is a current induced?

A

when the conductor is part of a complete circuit

26
Q

how is AC generated in alternator?

A

as one side of coil moves up through magnetic field - produced PD in one direction
- other side of coil moves down so pd changes direction

27
Q

how is DC generated in dynamo?

A
  • as coil rotates , it cuts through field lines –> induced PD
  • split ring commutator chnges connections between brushes and coil every time coil is perpendicular to magnetic field , so coil moves in same direction
28
Q

purpose of split ring commutator?

A

changes the current direction every half turn

29
Q

how do microphones use the generator effect? and function of microphone?

A
  • sound waves cause diaphragm to vibrate
  • diaphragm causes coil to VIBRATE
  • coil cuts field lines –> induced alternating PD of coil, bc coil always changes direction

Convert sound waves into variations in current

30
Q

what do transformers do and consist of?

A

used to increase/decrease pd of alternating current
- primary coil
- secondary coil
- iron core

31
Q

how do transformers work?

A

AC supplied to primary coil –> means it will produce changing magnetic field around coil
- The iron core is easily magnetised, so the changing magnetic field passes through it
- changing magnetic field cuts through secondary coil –> induces an alternating PD (as field is alternating)

  • alternating PD will have same frequency to AC supllied to primary coil
  • if the secondary coil is part of circuit - cause AC current to flow
32
Q

what does output PD of transformer depend on?

A
  • no. turns on primary/secondary coil
  • input pd
33
Q

difference between step up and step down trasnformers?

A

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

step down - decrease volatge
- less turn on secondary coil than primary

Physics (11 decks)

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