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physics qma revision 2018 Flashcards

1
Q

how to convert milliamps to amps

A

/ 1000

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2
Q

how to convert megavolts to volts

A

x1,000,000

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3
Q

function of ammeter

A

measures current

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4
Q

function of voltmeter

A

measures potential difference (voltage)

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5
Q

function of fixed resistor

A

allows a specific amount of current and voltage through

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6
Q

function of thermistor

A

as the temperature changes, the resistance changes

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7
Q

function of diode

A

only allows current to flow in one direction

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8
Q

function of light dependant resistor

A

as the light changes the resistance changes

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9
Q

what does resistance do

A

slows the flow of electrons in the circuit

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10
Q

what does high resistance mean

A

low current
low energy
higher potentail difference

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11
Q

what is ohms law

A

current is directly proportional to potential difference as long as the temperature is constant

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12
Q

what is a component that obeys ohms law called

A

an ohmic conductor

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13
Q

what is a series circuit

A

current is the same around the circuit
voltage splits but adds up what you put in
resistance gets added together

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14
Q

what is a parallel circuit

A

voltage is the same around the circuit
current splits but adds up what you put in
resistance is smaller than your lowest resistor

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15
Q

what happens as you increase the temperature on a thermistor

A

decrease the resistance

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16
Q

what happens as you increase the light on an ldr

A

descrease the resistance

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17
Q

how to calculate kinetic energy

A

0.5 x mass x speed^2

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18
Q

how to calculate gravitatinoal potential energy

A

mass x gravitational field strength x height

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19
Q

how to calculate power

A

energy transfered / time
work done / time
potential difference * current
current^2 x resistance

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20
Q

how to calculate efficiency

A

useful output energy transfer / total input energy transfer

useful power output / total power output

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21
Q

how to calculate charge flow

A

current * time

22
Q

how to calculate potential difference

A

current * resistance

23
Q

how to calculate energy transferred

A

power x time

charge flow x potential difference

24
Q

method to calculate resistance for a filament bulb

A
  • measure potential difference with a voltmeter
  • calculate resistance using V / I
  • independent variable (x axis) = potential difference
  • dependent variable (y axis) = current
25
Q

is a filament lamp an ohmic conductor

A

no

26
Q

why isn’t a filament lamp an ohmic conductor

A

the graph curves because the electrons gain kinetic energy and collide with vibrating ions more frequently, causing resistance and thermal energy being given off

27
Q

are fixed resistors ohmic conductors

A

yes

28
Q

how does steepness on an IV graph correspond with resistance

A

the steeper the gradient, the higher the resistance

29
Q

what is the independent variable in the length of the wire experiment

A

length of wire (x axst)

30
Q

what is the dependent variable in the length of the wire experiment

A

resistance (y axis)

31
Q

what is power measured in?

A

watts

32
Q

what colour is the earth wire and what is its function

A

yellow and green, prevents shocks and fires, 0v unless there is a problem

33
Q

what colour is the neutral wire and what is its function

A

blue, at or close to 0v

34
Q

what colour is the live wire and what is its function

A

AC, alternates between high positive and high negative voltage (230v)

35
Q

why are wires and pins made of metal

A

they have delocalised (sea of free electrons)

36
Q

why are plug case and outer insulations made of plastic

A

they do not conduct electricity

37
Q

what do transformers do

A

change the potential difference

38
Q

what do step up transformers do and why

A

increase the potential difference and decrease the current so its more efficient (less thermal energy is wasted from resistance in wire)

39
Q

what do step down transformers do and why

A

decrease the voltage and increase the current so the voltage is at 230V, safe for home levels

40
Q

what is power

A

the rate at which work is done

41
Q

what is work done

A

energy transferred

42
Q

what is current

A

the rate of flow of electron (charge) around a circuit

43
Q

what happens when two insulating materials are rubbed together

A

electrons only move, this means a material with more electrons than protons has a negative charge and the one with more protons has an equal but opposite positive charge

44
Q

what happens when a rod is rubbed on a polythene cloth

A

the rod becomes negative because it gains more electrons, the cloth becomes positive and has an equal and opposite charge to the rod

45
Q

what happens when a rod is rubbed on an acetate cloth

A

the rod becomes positive because it loses electrons so it has more protons than electrons, the cloth becomes negative and has an equal and opposite charge to the rod

46
Q

what is a danger of static electricity

A

sparks causing fuel to ignite e.g. in cars and planes

47
Q

how to earth a plane for refuelling

A

attach a metal cable, negative electrons will flow through. the charge will go from the plane to the ground and the charge will not build up instead it will be destroyed

48
Q

in electrical fields which way do the arrows flow

A

from positive to negative

49
Q

in electrical fields how can you increase the repulsion

A

by decreasing the distance

50
Q

in a comb and moving belt model how is the belt charged and why

A

the belt is positively charged because the belt loses negative electrons to the dome

51
Q

what happens when you touch the dome

A

your hair sticks up because of the negative charge

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