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physics > electricity and circuits - topic 9 > Flashcards

electricity and circuits - topic 9 Flashcards

1
Q

charge of neutrons

A

neutral

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2
Q

charge of protons

A

+1

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3
Q

charge of electrons

A

-1

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4
Q

is current shared or same in series circuit

A

same

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5
Q

is voltage shared or same in series circuit

A

shared

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6
Q

is current shared or same in a parallel circuit

A

shared

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7
Q

is voltage shared or same in a parallel circuit

A

same

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8
Q

difference between series and parallel circuit

A

In series, current only flows in 1 direction, components are all dependant on each other and they are all connected in 1 line

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9
Q

are voltmeters connected in parallel or series

A

parallel with a component to measure the voltage across it

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10
Q

are ammeters connected in parallel or series

A

in series with a component to measure the current in the component

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11
Q

what is electric current

A

the rate of flow of charge

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12
Q

what is current measure by and in

A

current is measure by an ammeter in amps

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13
Q

what is the conservation of current

A

current leaving positive terminal is the same amount as it is when it re enters through the negative terminal

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14
Q

what is charge measured in

A

coulombs

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15
Q

what is voltage

A

the energy transferred per coulomb of charge or the force required to push the electrons around the circuit

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16
Q

what is voltage measure by and in

A

voltage is measure by a voltmeter in volts

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17
Q

what is resistance

A

the opposition to the rate of flow of charge

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18
Q

what is resistance measure in

A

ohms

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19
Q

what causes a filament lamp to light and heat up

A

a potential difference across the filament lamp causes a current to flow through which cause it to light up and heat up.

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20
Q

why do diodes have very high resistance in one direction of circuit

A

to prevent the current from moving backwards

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21
Q

what is power

A

the amount of energy transferred every second

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22
Q

what is power measured in

A

watts

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23
Q

what is AC

A

alternating current is the forward and backward movement of charge

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24
Q

what is DC

A

direct current is the movement of charge in only 1 directions

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25
Q

what is the brown wire

A

the live wire

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26
Q

what is the green and yellow wire

A

the safety wire

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27
Q

what is the blue wire

A

the neutral wire

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28
Q

what is a fuse

A

a fuse is a safety feature which will overheat and melt and therefore break the circuit, if current surpasses the amount and is too high

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29
Q

what is a circuit breaker

A

a safety feature which will break the circuit if it detects changes in current

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30
Q

difference between circuit breaker and fuse

A

circuit breaker don’t have to be replaced unlike fuses

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31
Q

equation for power(1)

A

power = current^2 x resistance

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32
Q

equation for energy (1)

A

energy = current x time x voltage

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33
Q

equation for power (2)

A

power = current x voltage

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34
Q

equation for energy (2)

A

energy = power x time

35
Q

equation for charge

A

charge = current x time

36
Q

equation for energy (3)

A

energy = charge x voltage

37
Q

equation for voltage

A

voltage = current x resistance

38
Q

what is current in metals

A

a flow of electrons

39
Q

what happens when there is an electric current in a resistor

A

there is an energy transfer which heats the resistor

40
Q

what happens to electrical energy when an electric current does work against electrical resistance

A

electrical energy is dissipated as thermal energy in the surroundings

41
Q

why is electrical energy dissipated as thermal energy in the surroundings

A

free electrons collide with the ions that make up the lattice. These collisions transfer energy from the electrons to the ions, making the ions vibrate and causing the resistor to heat up

42
Q

how does the resistance of a thermistor vary with change if temperature

A

in hot conditions, resistance drops
in cool conditions, resistance goes up

43
Q

how does the resistance of an LDR vary with light intensity

A

in bright light, resistance falls
in darkness, resistance is highest

44
Q

how do you investigate the resistance of thermistors

A

place the thermistor in a water bath and pour enough water in to cover the thermistor

turn on the water bath

measure and record the temperature of the water using a thermometer

measure the current through the circuit for every 5 degree increase in temp

the potential difference needs to be kept constant throughout

use the pd of the power supply and values of current recorded to calculate resistance of the thermistor at each temp

you should find as temp increases, resistance decreases

45
Q

how do you investigate the resistance of LDR’s

A

in a darkened room, use a torch to shine a light on the LDR

record the distance between the torch and LDR

gradually move the torch away from the LDR so the intensity of the light hitting the LDR will decrease

recocrd the current through the LDR every 10cm you move the torch

use resistance = voltage/current to calculate resistance of the LDR for different light intensities

you should find as the torch moves away, resistance increases

46
Q

what does an I-V graph look like for a fixed resistor

A

you get a straight line , because the current through a fixed resistor is directly proportional to voltage

47
Q

what does an I-V graph look like for filament lamps

A

you get a curve because resistance increases with temperature so as more current flows through the lamp, the lamp heats up more and resistance increases. This means less current can flow per unit potential difference, so graph gets shallower

48
Q

what does an I-V graph look like for thermistors

A

a curve, because as a current flows through the thermistor the thermistor heats up. this causes the resistance of thermistor to decrease so the graph becomes steeper

49
Q

what does an I-V graph look like for LDR’s

A

straight line, because the resistance of an LDR only depends on light intensity

50
Q

how are series circuits connected

A

the different components are connected in a line end to end between the positive and negative ends of the power supply except the voltmeter

51
Q

what happens if one component is removed or disconnected in a series circuit

A

the circuit is broken and they all components stop

52
Q

why are series circuits built and designed in this way

A

to test and measure components

53
Q

total circuit potential difference in a series circuit =

A

voltage across component 1 + voltage across component 2 + …….

54
Q

total current flowing in a series circuit =

A

current through component 1 = current through component 2 = ……

55
Q

total resistance in a series circuit =

A

resistance of component + resistance of component 2 + ..

56
Q

source potential difference in parallel circuits =

A

pd across component 1 = pd across component 2 = …..

57
Q

total current flowing in parallel circuits =

A

current through branch 1 + current through branch 2 + ….

58
Q

if two resistors are in parallel, why is the net resistance decreased

A

by adding another additional loop, the current has more than one direction to go in which increases the total current that can flow around the circuit and using V =IR an increase in current means a decrease in total resistance

59
Q

what are the differences between series and parallel circuits

A

current through all components in series is the same, in parallel it depends on the resistance of each component

the total pd is shared across components in series and depends on its resistance

the total resistance of components in series is the sum of all the components resistances, but total resistance in parallel decreases as more components are added

60
Q

how do you investigate resistors in circuits

A

construct a circuit with a resistor, ammeter and a battery

measure the. current through the circuit with the ammeter

use current and pd of the battery to calculate resistance

use R = V/I

add another resistor in series or parallel

measure the current through the circuit and use the pd of the battery to calculate overall resistance

repeat until you have added all your resistors

plot a graph of number of resistors against total resistance

61
Q

how is energy transferred from different domestic devices

A

kettles transfer energy electrically from the mains a.c. supply to the thermal energy store of the heating element inside the kettle

62
Q

how can you reduce unwanted energy transfer

A

by using low resistance wires, as less energy will be transferred to the thermal energy stores

63
Q

what are the advantages of the heating effect of an electric current

A

fuses will melt and break the circuit if the current gets too high which prevents fires and electrical shocks

64
Q

what are the disadvantages of the heating effects of an electrical current

A

it reduces the efficiency of a process as less energy is transferred to useful energy stores

it can cause components in a circuit to melt, so circuits won’t work properly

65
Q

what is power

A

energy transferred per second

66
Q

what is power measured in

A

watts

67
Q

what is the relationship between power ratings for domestic electrical appliances and the changes in stored energy when they are in use

A

the lower the power rating, the less electricity an appliance uses in a given time, so the cheaper it is to run

68
Q

what does the power rating tell you

A

the maximum amount of energy transferred between stores per second when the appliance is in use

69
Q

how is power transfer related to the pd across it and the current in it

A

the higher the voltage or current, the more powerful the appliance

70
Q

what is the movement of charge like in a.c.

A

the charges are constantly changing direction

71
Q

is the domestic supply in the UK a.c. or d.c.

A

alternating current

72
Q

what is the frequency of the UK domestic main supply

A

50Hz

73
Q

what is the voltage of the UK domestic main supply

A

230V

74
Q

what is direct current

A

the movement of charge in one direction only

75
Q

do cells and batteries supply a.c. or d.c.

A

direct current

76
Q

what is the difference between direct and alternating voltage

A

direct voltage is when the positive and negative ends of the source are fixed

77
Q

what is the difference in function between the live and neutral mains input wires

A

the live wire provides electricity form the main supply and current flows in through the live wire

the neutral wire carries away current

78
Q

what is the pd between the live, neutral and earth mains wires

A

pd between live and neutral wire is 230V

pd between live and earth wire is 230 V

pd between neutral and earth wire is 0V

79
Q

what is the danger of providing any connection between live wire and earth

A

if the link creates a low resistance path to the earth, a huge current will flow, which would result in a fire

80
Q

why should switches and fuses be connected in the live wire of a domestic circuit

A

if there was a problem, the supply of electricity to the appliance can be cut off

81
Q

what is the function of fuses in ensuring safety

A

if the current increases beyond a certain point, the wire gets too hot and melts. The fuse blows and the circuit is broken and electricity cannot flow

82
Q

what is the function of earth wires in ensuring safety

A

earth wire is connected to the metal casing, which provides a low resistance path for a current to travel down in the event of a fault and as the resistance is low, a large current flows, causing a current surge which metls the fuse

83
Q

what is the function of circuit breakers in ensuring safety

A

a large current will trip a circuit breaker quicker than it takes a fuse to melt and they can be reset instead of replaced

physics (14 decks)

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