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A level physics > Electricity > Flashcards

Electricity Flashcards

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1
Q

What is current?

A

It is defined as the number of coulombs transferred per second (rate of flow of charge).
It is the flow of electrons.

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2
Q

What is potential difference?

A

It is defined as the energy transferred per coulomb

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3
Q

What is resistance?

A

This describes how difficult electrons find it to move through a wire/component

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4
Q

What is power?

A

It is the rate at which electrical energy is supplied to a circuit.

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5
Q

What is the unit for charge?

A

Coulombs(C)

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6
Q

What is the unit for current?

A

Amps(A)

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7
Q

What is the unit for resistance?

A

Ohms

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8
Q

What is the unit for work done?

A

Joules

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9
Q

What is the unit for power?

A

Watts/joules

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10
Q

What is the equation that links charge, current and time?

A

Charge = current*time

Q=IT

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11
Q

What is the equation that links P.D, current and resistance?

A

P.D = current*resistance

V=IR

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12
Q

What is the equation that links P.D, work done and charge?

A

P.D = work done / charge

V=J/Q

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13
Q

What is the equation that links power, current and P.D?

A

Power = current*P.D

P=IV

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14
Q

What is the equation that links power, P.D and resistance?

A

Power = P.D^2/resistance

P=V^2/R

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15
Q

What is the equation that links power, current and resistance?

A 
Power = current^2 * resistance
P= I^2*R
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16
Q

What is Ohm’s law?

A

The current through an ohmic conductor is directly proportional to the voltage provided the physical conditions such as temperature remain the same

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17
Q

What factors can affect resistance?

A

Temperature
Light intensity
Type of wire
Length of wire

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18
Q

How does the I/V graph for an ohmic conductor look like?

A

Straight line through the origin

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19
Q

How does the I/V graph for a filament lamp look like?

A

It is a curve

Begins steep and becomes shallower as the current increases

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20
Q

Why does a filament lamp I/V graph become shallower as the current and voltage increase?

A

The temperature and resistance increase as the current flows through the lamp

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21
Q

Why does the resistance of a metal increase as the temperature increases?

A

The atoms in the metal gain energy from the rising temperature
The atoms vibrate faster
This makes it harder for electrons to move past the metal atoms

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22
Q

What are semiconductors?

A

Semiconductors are conductors that do not conduct electricity as well as metals as they have fewer charge carriers

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23
Q

What happens when energy is supplied to a semiconductor?

A

More charge carriers are released

This makes them excellent sensors for detecting changes in their environment

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24
Q

Give two examples of semiconductors

A
  • Thermistors

- Diodes

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25
Q

What is a thermistor?

A

It is a resistor

The resistance depends on temperature

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26
Q

What happens when the temperature increases in a thermistor?

A

As the temperature increases, the resistance decreases

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27
Q

Why does the resistance decrease as the temperature increases in a thermistor?

A

As the temperature increases, more electrons have enough energy to escape from their atoms
This means that there are more charge carriers available

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28
Q

In which direction does the current flow in a diode?

A

The current flows in the direction that the triangle in the symbol points

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29
Q

What is the threshold voltage for most diodes in the forward bias?

A

O.6V

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30
Q

What happens to the current in a diode after the threshold voltage?

A

The current rapidly increases

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31
Q

What are the three factors that affect resistance of a material?

A
  • Length
  • Area
  • Resistivity
32
Q

How does length affect resistance?

A

The longer the wire, the further the current has to travel and the more difficult it is to flow a current through the wire

33
Q

How does area affect resistance?

A

The wider the area, the easier it is for current to pass through

34
Q

How does resistivity affect resistance?

A

The lower the resistivity, the more current can pass through and the lower the resistance

35
Q

What is the definition of resistivity?

A

The resistivity of a material is defined as the resistance of a 1m length with a 1m^2 cross-sectional area.
Measured in ohms-meters

36
Q

What is the equation that is used to find resistivity?

A

Resistivity= (resistance*area)/length

37
Q

Why are metals good conductors?

A

They have low resistivity

38
Q

What happens when there is low resistivity?

A

There is a high current flow

39
Q

What are superconductors?

A

Conductors which have zero conductivity at and below the critical temperature

40
Q

How are superconductors made?

A

Superconductors are cooled to their critical temperature

41
Q

How can the critical temperature be increased from -273 to -123?

A

Using new materials called cuprates(copper oxide)

42
Q

Why is no energy lost as heat in superconductors?

A

There is no resistance and therefore no potential difference

43
Q

What are the uses for superconductors?

A

1-power cables that transmit electricity without any loss of power
2-high power electromagnets(MRI scanners, Maglev trains)
3-electronic circuits

44
Q

How do you find the resistivity of a wire?

A
  • Use a micrometre to measure the diameter of the wire
  • Use this length to find the radius and then calculate the cross-sectional area
  • Clamp the test wire to a ruler with the circuit attached to the wire where the ruler reads zero
  • Attach the flying lead to the test wire
  • Record the length of the test wire connected to the circuit, the voltmeter reading and ammeter reading
  • Calculate the resistance using the voltmeter and ammeter readings
45
Q

How can you increase the accuracy of the diameter measured?

A

Measuring the diameter at three different points along the wire and calculate an average

46
Q

When conducting the experiment, why must the temperature be kept constant?

A

The resistivity of a material depends on its temperature

47
Q

How can you try to keep the temperature of the wire constant?

A

Having only small currents flow through the wire or else the current will cause an increase in temperature leading to invalid results and random errors

48
Q

What happens to the current in a series circuit?

A

The current is the same throughout the circuit

49
Q

What happens to the voltage in a series circuit?

A

It is shared between all the components attached

50
Q

What happens to the current in a parallel circuit?

A

The total current is the sum of the currents throughout each branch

51
Q

What happens to the voltage in a parallel circuit?

A

The voltage supplied is the same throughout each branch

52
Q

How do you calculate the total resistance in series?

A

Total R = R1+R2…

53
Q

How do you calculate the total resistance in parallel?

A

1/total R=1/R1 + 1/R2…..

54
Q

What is EMF?

A

Electromotive force

the inherent voltage of the cell

55
Q

How do you calculate EMF?

A

E= I(R+r)

56
Q

What does ‘r’ mean?

A

internal resistance

57
Q

What does ‘R’ mean?

A

external resistance

58
Q

Why is the voltage not always equal to the EMF?

A

this is because of the internal resistance in the cell

59
Q

How do you calculate the voltage in a circuit?

A

V=EMF-P.D(lost in the source)

60
Q

what happens when the circuit is open?

A

There is no current flow which means that there is no P.D

Therefore the voltage = EMF

61
Q

What happens when the P.D increases?

A

the current decreases and the resistance increases

62
Q

What is internal resistance?

A

The opposition to the flow of charge through the source

63
Q

What happens to the electrical energy?

A

it is dissipated inside when the charge flows

64
Q

How do you calculate the EMF using electrical energy?

A

EMF = electrical energy/charge

65
Q

How do you calculate the lost P.D?

A

Lost P.D = EMF - P.D(throughout the circuit)

66
Q

How do you calculate the power supplied by the cell?

A

IE=I^2R + I^2r

Power = power to R + power wasted in the cell

67
Q

When is max power delivered?

A

Max power is delivered when the resistance = internal resistance

68
Q

How do you calculate the EMF in multiple cells in series?

A

total EMF = EMF1+ EMF2…..

69
Q

How do you calculate the EMF in multiple cells in parallel?

A

total EMF = EMF1 = EMF2=EMF3…..

70
Q

How do you find the emf and internal resistance using a graph?

A

EMF = y-intercept
internal resistance = gradient(-r)

y=mx+c
V= -rI+EMF

71
Q

How do you calculate the total energy in a circuit?

A 
Energy = VIt
Energy = P.D *current*time(secs)
72
Q

What is a potential divider?

A

A circuit with a voltage source and resistors in series

73
Q

How do you calculate the voltage out of the circuit?

A

Vout = (Vin * R2)/R1+R2

74
Q

What is 1 Coulomb(C)?

A

It is defined as the amount of charge that passes in 1 second if the current is 1 ampere(A)

75
Q

What is a volt?

A

The potential difference across a component is 1 volt when you convert 1 joule of energy moving 1 coulomb of charge through the component

76
Q

What is an ohm?

A

A component has a resistance of 1ohm if a potential difference of 1V makes a current of 1A flow through

77
Q

What is resistivity of a material?

A

The resistivity o a material is defined as the material of a 1m length with a 1m^2 cross-sectional area

A level physics (15 decks)

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