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Physics section 4 Electromagnetism > E.I.N.T.K > Flashcards

E.I.N.T.K Flashcards

1
Q

define electrical field

A

it is a region where a charge that experiences a force

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2
Q

define magnetic field

A

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

it is a region around a magnet where another magnet experiences a force

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3
Q

describe an electric field around a point charge

A

positive point charge: arrows go away from the atom

negative point: arrows go towards the atom

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4
Q

which direction does current flow in, in an electric field

A

arrows go from north to south, left to right if vertical

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5
Q

describe how to charge a body by static electricity

A
  1. start off by having a neutral body
  2. bring a positively charged rod towards the body (all electrons will move to the side with the rod)
  3. connect the body to earthing (this will bring in more electrons)
  4. remove earthing first to be stuck with a negative charge
  5. remove rod last
    the above is to negatively charge a neutral body so do the opposite to positively charge a neutral body
  • *in step 2 use a -ve charged rod
  • *in step 3 when earthing is connected electrons flow into the earth
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6
Q

describe 3 methods of magnetising

A
  1. stroking method - stroke a ferrous unmagnetised material with a north pole of a strong magnet and repeat many times
  2. electrical method - wind a wire round a ferrous material and run a direct current through it
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7
Q

methods of demagnetisation

A
  1. hammering
  2. hit
  3. using an alternating current
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8
Q

same currents…

A

attract

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9
Q

opposite currents…

A

repel

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10
Q

what is a galvanometer

A

it is a sensitive ammeter

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11
Q

describe what happens when a magnet passes through a galvanometer

A
  1. deflection then reverse deflection
    (when a north pole passes through)
  2. deflection is larger
    (when a south pole passes through first)
  3. as the magnet moves the coil cuts the magnetic field lines inducing an EMF
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12
Q

ways to increase induced EMF

A
  1. move the magnet faster - faster speed
  2. put more turns on the coil
  3. use a stronger magnet
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13
Q

describe features of a motor

A

split ring commutator - turns with the coil. each time the coil reaches a vertical position the commutator swap brushes and flow of current is reversed. this means the direction of force is reversed and the coil keeps spinning in the same direction

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14
Q

what can cause a motor to spin faster

A
  1. bring magnets closer
  2. use a stronger magnet
  3. more turns in a magnet/coil
  4. stronger current
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15
Q

state the effect of reversing the connections to the battery in a motor

A

direction of rotation is reversed

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16
Q

describe how an EMF is induced in an a.c. generator

A
  1. as the coil rotates one side cuts up the magnetic field lines inducing an e.m.f causing a current to flow
  2. when the coil reaches the vertical postion, the side that was cut up is now cut down - induced e.m.f will change direction as well as current
17
Q

what does an alternating current look like on a graph

A
  • similar to sine graph
  • V or I on y axis
  • time on x axis
18
Q

what is the purpose of a variable resistor

A

it controls the amount of current passing through a component (e.g. heater) changing its resistance

19
Q

what happens when an ammeter reading decreases

A
  1. batteries go flat

2. resistance increases decreasing current

20
Q

the temperature of a thermistor increases so that its resistance decreases
state the effect of this change on the current - explain your answer

A

current increases as total resistance of the circuit decreases

21
Q

suggest an advantage of being able to change the current

A

it prevents overheating

22
Q

describe in terms of current the difference between a big and small wire

A

big wire: more current and power, less resistance

small wire: less current and power, more resistance

23
Q

what happens when a bigger wire is used instead of a smaller wire

A

power loss is decreased to about quarter of original power as resistance decreases

24
Q

state 2 sensor devices

A

LDR

Thermistor

25
Q

describe action in a thermistor

A
  • when temperature increases (not if the thermistor) resistance decreases
  • when temperature decreases the resistance increases
26
Q

describe action of a LDR

A
  • when light intensity increases resistance decreases

- when light intensity decreases resistance increases

27
Q

what happens to resisitance when V or I or P increases

A

resistance decreases

28
Q

what is a potential divider

A

just a circuit with 2 resistors

29
Q

a circuit has a LDR in series with a resistor and a lamp across the resistor
what change is made in the circuit to make the lamp glow brightly

A

-increase current flowing through the lamp by increasing the voltage across it through increasing light intensity of the LDR which will reduce the resistance

30
Q

describe a circuit in series

A
  1. current is the same through out
  2. all components are switched on at the same time
  3. voltage is shared/divided meaning different brightness in lamps
  4. if one lamp is faulty whole circuit breaks
31
Q

describe a circuit in parallel

A
  1. current is divided/shared
  2. voltage is the same through out
  3. switched on/off individually
32
Q

in a transformer why is the iron core laminated

A

to reduce energy loss

33
Q

how is an emf induced in a transformer

A

the a.c. emf at the primary coil induces a magnetic field in the iron core. this alternating magnetic field is cut by the secondary coil producing an EMF in the process

34
Q

formulas in transformers

A 
Np/Ns = Vp/Vs
VpIp = VsIs
35
Q

state 3 methods of charging objects

A
  1. rubbing
  2. induction
  3. earthing

Physics section 4 Electromagnetism (1 decks)

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