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Physics > Unit 1: Electric Current and Direct Current Circuits > Flashcards

Unit 1: Electric Current and Direct Current Circuits Flashcards

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0
Q

What is electric current?

A

The rate of flow of charge.

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1
Q

What needs to happen in order to pass an electric current around a circuit?

A

The circuit must be complete and there must be a source of potential difference.

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2
Q

What is the current due to?

A

The passage of charge carriers.

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3
Q

What happens when a current passes through a metal?

A

The charge carriers are electrons and they collide with each other and the fixed positive ions in the metal.

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4
Q

What is conventional current?

A

When the direction of current goes from the positive terminal to the negative terminal. It is opposite to the flow of electrons.

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5
Q

What is the unit for current?

A

Ampere

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6
Q

What is the unit for charge?

A

Coulomb

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7
Q

What is one coulomb equal to?

A

The charge flow in one second when the current is one ampere.

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8
Q

What is the symbol for charge?

A

Q

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9
Q

Why does an insulator not conduct electricity?

A

Each electron is attached to an atom and cannot move away from it.

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10
Q

What happens to the number of charge carriers in a semiconductor as temperature increases?

A

The number of charge carriers also increases. The resistance therefore decreases.

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11
Q

What happens in an intrinsic semiconductor?

A

Electrons break free from the atoms of the semiconductor.

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12
Q

What do electrons deliver from the battery to the components?

A

Energy

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13
Q

What does the battery supply each electron with?

A

Electrical potential energy

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14
Q

What is the work done by an electron equal to?

A

The loss of potential energy.

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15
Q

What is potential difference/voltage?

A

The work done per unit charge.

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16
Q

What is the emf of a source?

A

The electrical energy produced per unit charge passing through the source.

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17
Q

What is electrical energy produced equal to?

A

Charge x emf

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18
Q

What may happen due to a source’s internal resistance?

A

Some energy may be dissipated

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19
Q

What effect does an electric current passing through a component have?

A

A heating effect and a magnetic effect.

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20
Q

What is power equal to?

A

Energy/time

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21
Q

How do you calculate power?

A

IV

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22
Q

What is the unit for power?

A

Watt

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23
Q

What is resistance?

A

A measure of the difficulty of making current pass through the component.

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24
Q

What is resistance caused by?

A

Repeated collisions between the charge carriers and the fixed positive ions in the metal.

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25
Q

How can you calculate resistance?

A

V/I

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26
Q

What is the unit of resistance?

A

Ohm

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27
Q

How do you connect an ammeter?

A

In series

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28
Q

How do you connect a voltmeter?

A

In parallel

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29
Q

Why must no current pass through the voltmeter?

A

So that the ammeter can accurately record the current passing through the component.

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30
Q

What is the gradient of a pd/current graph?

A

Resistance

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31
Q

What is the gradient of a graph when current is plotted on the y axis and pd on the x axis?

A

1/R

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32
Q

What is ohm’s law?

A

The pd across a metallic conductor is proportional to the current through it, provided the physical conditions do not change.

33
Q

What is resistance equal to in terms of resistivity?

A

PL/A where p is resistivity (a constant)

34
Q

What is the unit of resistivity?

A

Ohm metre

35
Q

What is a superconductor?

A

A wire or device made of material that has zero resistivity at and below a critical temperature that depends on the material.

36
Q

Why does the current have no heating effect when it passes through a superconductor?

A

There is no resistance therefore there is no potential difference.

37
Q

When does a superconductor lose its superconductivity?

A

If it’s temperature is raised above its critical temperature.

38
Q

What are superconductors used to make?

A

High-power electromagnets that generate very strong magnetic fields and power cables that transfer electrical energy without wasting energy.

39
Q

What is a battery?

A

A combination of cells.

40
Q

What is a cell?

A

A source of electrical energy.

41
Q

What does a diode do?

A

It allows current to flow in one direction only.

42
Q

What happens when a light-emitting diode conducts?

A

It produces light.

43
Q

What is referred to as the forward direction?

A

The direction in which the diode conducts.

44
Q

What is referred to as the reverse direction?

A

The opposite direction to which the diode conducts.

45
Q

When is a diode used?

A

To protect dc circuits.

46
Q

What happens to the resistance of a thermistor with increasing heat?

A

It decreases.

47
Q

What happens to the resistance of a light dependent resistance with increasing light?

A

It decreases.

48
Q

What can you use to measure the variation of current with pd?

A

A potential divider to vary the pd from zero or a variable resistor to vary the current to a minimum.

49
Q

For a current and pd graph for a thermistor, which temperatures would provide a steeper gradient?

A

High temperatures.

50
Q

Why does the graph for a filament bulb have a decreasing gradient?

A

It’s resistance increases as it becomes hotter.

51
Q

When does a silicon diode start to conduct?

A

0.6V

52
Q

Why does resistance increase when temperature does?

A

The positive ions in the metal vibrate more when the temperature is increased. The charge carriers therefore cannot pass through as easily as before, it is said to have a positive temperature coefficient.

53
Q

What type of temperature coefficient does an intrinsic semiconductor have?

A

Negative

54
Q

What is critical temperature also know as?

A

Transition temperature.

55
Q

What is the case at any junction in a circuit?

A

The total current leaving the junction is equal to the total current entering the junction.

56
Q

Do components use up current?

A

No

57
Q

How is current distributed amongst more than two components in a series circuit?

A

The current reaching each of the components is the same.

58
Q

What happens if he charge carriers lose energy?

A

The potential difference is a potential drop

59
Q

What happens if the charge carriers gain energy?

A

There is a potential rise

60
Q

What is the rule for pd in series circuits across the components?

A

The total pd of the circuit is equal to the sum of the pd of each component.

61
Q

What is the sum of the emfs in a loop equal to?

A

The sum of the pds.

62
Q

In a series circuit what is the total resistance equal to?

A

The sum of the individual resistances.

63
Q

What is the total resistance in a parallel circuit given by?

A

1/R=1/R1+1/R2 …

64
Q

What happens when a charge carrier loses energy due to a collision?

A

The force of the pd causes it to accelerate until it collides with another positive ion.

65
Q

What are other ways of expressing power?

A

I^2R or V^2/R

66
Q

Does power supplied depend on the direction of current?

A

No

67
Q

How can you calculate energy transferred?

A

I^2Rt

68
Q

Why is the terminal pd less than the emf?

A

Internal resistance

69
Q

What is internal resistance?

A

The loss of potential difference per unit current in the source when the current passes through the source.

70
Q

How can you calculate emf according to internal resistance?

A

E=Ir+IR

71
Q

What is the power supplied by the cell equal to?

A

IE=I^2R+I^2r

72
Q

When is maximum power delivered to a load?

A

When load resistance is equal to the internal resistance.

73
Q

What is the gradient of a terminal pd/current graph equal to?

A

Internal resistance

74
Q

What is the y intercept of a terminal pd/current graph equal to?

A

The emf

75
Q

What happens to the terminal pd as the current increases.

A

It decreases

76
Q

What is terminal pd?

A

Emf at zero current

77
Q

How can you calculate terminal pd?

A

E-Ir

78
Q

What does a potential divider consist of?

A

Two resistors in series with a source of fixed potential difference.

79
Q

What is the ratio of pds across each resistor equal to?

A

The resistance ratio of the two resistors.

80
Q

What can a variable potential divider be used for?

A

To change the loudness of a sound from a loud speaker or to vary the brightness of a light bulb.

Physics (18 decks)

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