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A - Physics GCSE > Topic 6 - Electric and Magnetic Fields > Flashcards

Topic 6 - Electric and Magnetic Fields Flashcards

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1
Q

What is a build up of static caused by?

A

Frictional forces

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2
Q

how does rubbing an insulator transfer electrons and create a static charge

A

negatively charged electrons are scraped off one material onto another

  • as its an insulator the electrons aren’t free to move
  • this builds up static electricity
  • the material becomes electrically charged with a positive static.
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3
Q

Which charged particles are always moved

A

negative electrons

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4
Q

Electrically charged particles exert a ……on each other

A

force

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5
Q

how do forces of attraction change with distance

A

further means weaker

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6
Q

How can an electrically charged object attract uncharged objects (with example)

A

Rubbing a balloon on your head transfers electrons to the balloon leaving it negatively charged
-if you hold the balloon against a wall it will stick because the negatively charges on the wall are repelled and positive charges are attracted to negative balloon

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7
Q

How does attraction by induction occur

A

If a negatively charged object is used to charge a neutral object by induction, then the neutral object will create a positive charge.
(The charged object that is brought near will always repel like charges and attract opposite charges.)

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8
Q

What is earthing

A

sending current down to the earth

provides easy route for static charge so none builds up

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9
Q

How do spark occur

A

If a potential difference is large enough, electrons can jump a gap between charged object and earth making a spark
eg)lightning

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10
Q

Too much static causes….

A

sparks

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11
Q

Why might you get an electric shock getting out of a car

A

static charge builds up on car

static charge jumps to earthed conductor nearby being you and you get a shock

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12
Q

How do electrostatic sprayers work

A
  • spray gun is charged, so paint droplets become negatively charged
  • object being painted has an opposite charge to attract the fine sprays of paint
  • gives an even coat as areas with paint become negative so theres no build up
  • no paint shadows
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13
Q

why is static dangerous in fueling cars/aircraft

A

as fuel flows out of pipe into tank, static can build up which can lead to sparks which might cause an explosion in dusty places

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14
Q

Why is static on planes dangerous and how does it occur

A
  • as a plane flys through the air, friction between the air and plane builds up causing plane to become charged
  • this static can interfere with communication equipment
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15
Q

How does lighting form

A

raindrops and ice bump causing friction and leaves top of cloud positively charged and bottom negative which creates huge voltage and spark which jumps across gap to earth as lightning
-damage homes, start fires

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16
Q

How can objects be earthed to stop charge building up

A

by connecting charged object to the ground using conductor through earthing

  • provides easy route for static charge
  • no build up of static so no sparks
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17
Q

How do electrons flow to ground by earthing if ground charge is:
negative
positive

A

Negative= flow down the conductor

Positive= flow up the conductor

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18
Q

What do electric charges do

A

Create an electric field around any charged object

stronger as you get closer

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19
Q

How is the direction of an electric field defined

A

Field lines go FROM positive TO negative

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20
Q

What happens to a charged object is placed in an electric field? and what is it caused by?

A

it feels a force caused by two charged objects interacting

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21
Q

what happens field lines between charged objects point in opposite directions

A

They repel

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22
Q

How do you get a uniform field

A

between two positively charged parallel plates

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23
Q

How can sparking be explained with electric fields (and therefore static)

A
  • When an object is statically charged it creates its own electric field
  • interactions in this field cause sparking
    eg) plastic comb becomes charged and produces an electric field which can interact with paper without touching them
24
Q

What is ionisation in a electric field

A

Electrons in the air particles to be removed

25
Q

When is air not an insulator

A

when its ionised enough that it becomes more conductive and sparks are made

26
Q

What do magnets produce

A

magnetic fields

27
Q

Where do field lines go to in a magent

A

north to south

28
Q

the closer the field lines the …..the magnetic field

A

stronger

29
Q

where is the magnetic field strongest at

A

the poles

30
Q

What are the 3 main magnetic elements

A

iron, nickel, cobalt

some alloys containing these will also be magnetic like steel

31
Q

What is a permanent magnet

A

produces its own magentic field

32
Q

What is an induced magnet

A

only produces a field when in another magnetic field

putting any magnetic material into a magnetic field it becomes an induced magnet

33
Q

What is magnetic induction

A

force between magnet and magnetic material is always attractive

34
Q

What does magnetically soft mean and give examples

A

Lose their magnetism very quickly

pure iron and nickel iron alloys

35
Q

what does magentically hard mean and give examples

A

lose there magnetism more slowly

permanent magnets are made from magnetically hard materials

36
Q

Name some uses of magnetic fields

A

Doorbells- electromagnets that turn on and off rapidly to repeatedly attract and release an arm which strikes a metal bell

MRI machines- magnetic fields to creat images inside your body without having to use ionsing radiation

37
Q

A moving charge creates a

A

magnetic field

38
Q

explain the right hand rule

A

thumb represents current curled up fingers represent the direction of the magnetic field at right angles to the current

39
Q

in order to experience full force in a motor the wire needs to be at……

A

90 degrees to the magnetic field

if it runs along field it wont experience any force

40
Q

What is flemmings left hand rule

A

Used to explain the motor effect
Thumb = motion
first finger = field
second finger = current

41
Q

How can you find the size of a force

A

Force = magnetic flux density x current x length (of conductor)

42
Q

Describe how a motor works

A
  • forces (which act on current in magnetic field) act on two arms of a current carrying coil
  • they act in opposite directions so coil rotates
  • the split ring commutator swaps the contacts every half turn to keep motor rotating in same direction
43
Q

how can the direction of a motor be reversed

A

by swapping the polarity of the D.C supply or swapping the magnetic poles over

44
Q

What is a solenoid

describe the field lines:

A

a long coil of current carrying wire

- the field lines around each separate coil of wire line up in same direction so the field is strong and uniform

45
Q

why is a solenoid an electromagnet

A

-its an electromagnet as field can be turned off using electric current

46
Q

how can you increase strength of solenoid

A

by putting a block of iron in the center of coil which becomes an induced magnet

47
Q

what is electromagnetic induction in terms of Potential difference

A

induction of potential difference in a wire which is experiencing a change in magnetic field

48
Q

what two situations can you get electromagnetic induction

A

when electrical conductor (coil of wire) and magnetic field are relative to each other
-this can be done by rotating/ moving/ changing polarity of magnet

when magnetic field through conductor changes (like in a transformer)
-this can be done by increasing STRENGTH of magnetic field, increasing SPEED, increasing TURNS ON COIL

49
Q

How does a transformer work

A

-use electromagnetic induction to change size of Potential difference of an alternating current by: increasing number of coils on secondary coil than primary coil in step down

50
Q

How do dynamos work

A
  • generate a direct current by applying a force to rotate coil in magentic field (like in a motor)
  • current is induced in coil which changes direction every half turn due to split ring communicator to keep current flowing in same direction
51
Q

How do Alternators work

A
  • similar way to dynamos, force applied to rotate coil in magnetic field with an induced current in coil
  • but instead of split ring has slip rings and brushes so the contacts dont swap every half turn which produces and alternating current
52
Q

How do microphones work

A
  • using electromagnetic induction
  • sound waves hit diaphragm which is attached to coil of wire which makes both move creating a current in the coil

-

53
Q

How do loudspeaker work

A

-coil wrapped around pole of permanent magnet
so a.c signal causes a force on the coil
-when current reversed the force acts i different direction
-this moves the paper cone as it vibrates it as pressure causes sound waves

54
Q

Describe how a power station generates electricity for the national grid

A
  • burning fuel heats water which creates steam
  • steam powers turbine
  • turbine connected to powerful magnet inside generator
  • the magnet spins, inducing a large voltage and a.c current and single output generated
  • generator joined to national grid
55
Q

How are transformers used

A

The high current heats up wires so energy can be wasted so to reduce this transformers are used and high voltage cables.

  • Step up make Voltage really high at 400,000 V and keep current low (usually in less comercial areas like across country
  • step down decrease voltage to safe usable levels for consumers like in towns and homes

A - Physics GCSE (9 decks)

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