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Physics > 2 Current and voltage in circuits > Flashcards

2 Current and voltage in circuits Flashcards

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1
Q

What is an electric current?

A

It is a flow of charge.

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2
Q

What is a current?

A

It is the rate of flow of charge.

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3
Q

What are the charges carried by in metal wires?

A

By very small particles called electrons.

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4
Q

What does a material being a good conductor of electricity mean?

A

The material must let electrons flow easily throughout it.

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5
Q

Are metals good conductors of electricity?

A

Yes, because electrons can flow easily through them, making them good conductors.

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6
Q

What does a material being a poor conductor of electricity mean?

A

The material doesn’t enable electrons to easily pass through it, like plastic.

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7
Q

What do we call very poor conductors?

A

Insulators.

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8
Q

Are plastics insulators?

A

Yes, as they are poor conductors of electricity and do not let the electrons pass through them easily.

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9
Q

When are insulators useful?

A

They are useful in situations where we want to prevent the flow of charge. This can be observed in the casing of a plug.

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10
Q

Why are metals good conductors in relation to atoms?

A

This is because some electrons are free to move between the atoms

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11
Q

What do we mean by the random movement of electrons?

A

The number of electrons flowing in any one direction is roughly equal to the number flowing in the opposite direction.

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12
Q

What happens to the charge because of the random movement of electrons?

A

There is no overall flow of charge.

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13
Q

What happens to the charges in a conductor if a cell or battery is connected?

A

More of the electrons now flow in the direction away from the negative terminal, and towards the positive terminal rather than in the opposite direction.

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14
Q

What is this movement to the positive terminal of the conductor called?

A

There is now a net flow of charge. The flow of charge which is what we call an electric current.

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15
Q

What is the electric current in solid metallic conductors?

A

It is a flow of negatively charged electrons which are, obviously, delocalised.

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16
Q

Why do insulators block any electric current from entering?

A

All their electrons are held tightly in a position and are unable to move from atom to atom. Charges are therefore unable to move through insulators.

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17
Q

How do we measure the size of the current in a circuit?

A

Using an ammeter.

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18
Q

Where do you place the ammeter?

A

The ammeter is connected in series with the part of the circuit that we are interested in.

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19
Q

What is the circuit symbol for an ammeter?

A
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20
Q

What does the size of an electric current indicate?

A

The rate at which the charge flows.

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21
Q

What is the equation used to calculate the total charge that passes along a wire?

A

Q (charge) = I (Current A) x T (Time S)

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22
Q

What is voltage?

A

The amount of energy transferred to each coloumb of charge that passes.

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23
Q

What is the volt?

A

It is a joule per coloumb.

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24
Q

What is one singular jule per coloumb equal to?

A

A singular volt. So they are equal to each other.

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25
Q

What happens as the charges flow around a circuit?

A

The energy they carry is transferred by the components they pass through.

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26
Q

How can this be shown?

A
  • When current passes through a bulb, energy is transferred to the surroundings as heat and light.
  • When a current passes through the speaker of a radio, most of the energy is transferred by sound.
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27
Q

What is the equation for energy transferred?

A

E (Energy transferred J) =
Q(Charge coloumbs) x V (voltage volts)

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28
Q

How do we measure voltages?

A

Using a voltmeter

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29
Q

How do you place the voltmeter?

A

It is connected across (in parallel with) the component that we are investigating.

30
Q

What does a voltmeter connected across a cell or battery show?

A

It will measure the energy given to each coloumb of charge that passes through it.

31
Q

What does a voltmeter connected across a component show?

A

It will measure the electrical energy transferred when each coloumb of charge passes through it.

32
Q

What is the circuit symbol for a voltmeter?

A
33
Q

What does it mean when a circuit is complete?

A

When there are no gaps in the circuit. Charges are able to flow and if there are any bulbs attached they glow.

34
Q

What does it mean when a circuit is incomplete?

A

When there are gaps in the circuit, charges are not able to flow and if there are any bulbs attached they do not glow.

35
Q

What is the circuit symbol for a switch (open)?

A
36
Q

What is the circuit symbol for a switch (closed)?

A
37
Q

What is the circuit symbol for a cell?

A
38
Q

What is the circuit symbol for a battery?

A
39
Q

What is the circuit symbol for a diode?

A
40
Q

What is the circuit symbol for a fixed resistor?

A
41
Q

What is the circuit symbol for a variable resistor?

A
42
Q

What is the circuit symbol for a bulb?

A
43
Q

What is the circuit symbol for a fuse?

A
44
Q

What is the circuit symbol for a voltmeter?

A
45
Q

What is the circuit symbol for an ammeter?

A
46
Q

What is the circuit symbol for a thermistor?

A
47
Q

What is the circuit symbol for a light-dependent resistor (LDR)?

A
48
Q

What can we use to indicate the presence of a current in a circuit?

A

Lamps and Light Emitting Diodes (LED’s).

49
Q

What uses this method of checking that there is current in an appliances inner circuits?

A

TV’s, DVD’s and small routers use small LED’s to show when the appliance is working or on standby.

50
Q

What are the two main types of electrical circuit?

A
  • Series circuit.
  • Parallel circuit.
51
Q

What is a series circuit?

A

It is a circuit where there are no branches or junctions and there is only one path the current can follow.

52
Q

What is a picture of a series circuit?

A
53
Q

What is a parallel circuit?

A

It is a circuit that has branches or junctions and more than one path that the current can follow.

54
Q

What is a picture of a parallel circuit?

A
55
Q

What are the components of a series circuit containing bulbs?

A
  • All of the components can be controlled by a single switch.
  • If any one of the bulbs breaks, it causes a gap in the circuit and all the other bulbs will stop working.
  • The energy supplied by the cell is ‘shared’ between all the bulbs, so the more bulbs you add to a series circuit, the less bright they all become.
56
Q

From those components, which of them are advantages of series circuits?

A
  • All of the components can be controlled by a single switch.
57
Q

From those components, which of them are advantages of series circuits?

A
  • If any one of the bulbs breaks, it causes a gap in the circuit and all the other bulbs will stop working.
  • The energy supplied by the cell is ‘shared’ between all the bulbs, so the more bulbs you add to a series circuit, the less bright they all become.
58
Q

What kind of domestic lighting uses series circuits?

A

Decorative lights are often wired in series.

59
Q

Why do decorative lights use series circuits?

A

Each bulb only needs a low voltage, so even when the voltage from the mains supply is ‘shared’ out between them each bulb still gets enough energy to produce light.

60
Q

What happens if the filament in one of the bulbs breaks in the decorative light series circuit?

A

Then all the other bulbs will go out since the flow of the current will be disrupted as it can only go one way. Blocking the current means that the current can no longer flow to the other bulbs.

61
Q

What are the components of a parallel circuit containing bulbs?

A
  • Switches can be placed in different parts of the circuit to switch each bulb on and off individually, or all together.
  • If one bulb breaks, only the bulbs on the same branch of the circuit will be affected.
  • Each branch of the circuit receives the same voltage, so if more bulbs are added to a circuit in parallel they all keep the same brightness.
62
Q

Which of those components are advantages of parallel circuits?

A

All of them.

63
Q

What kind of domestic lighting uses parallel circuits?

A

The lights in your home are wired in parallel.

64
Q

How do we know that the lights in your home are wired in parallel?

A

We know this because the lights can be switched on and off separately, and the brightness of each light does not change when other lights are on or off.

65
Q

What happens to the other lights if a bulb breaks or is removed in a parallel circuit?

A

You can still use the other lights.
Christmas lights are most often used in parallel to ensure that they don’t break all the time because if they were in series, if one broke, all of them would break due to the current only being able to flow in one direction.

66
Q

What happens to the current in series circuits?

A

The current is the same in all parts, so current is not used up more than one component that the other.

67
Q

What does the size of current in a series circuit depend on?

A

It depends on the voltage supplied to it, and the number and type of the other components in the circuit.

68
Q

How could we prove what we just said?

A

Second identical sale is added in series the voltage will double and so the current will also double.

69
Q

What happens to the current in parallel circuits?

A

The currents will not be the same in different parts of the circuit. The types of components in each of the different parts will affect the currents.

70
Q

What in a parallel circuit must the number of electrons that flow into a junction at each second be equal to?

A

The number of electrons that leave each second.

71
Q

What is that action reffered to as?

A

The current being conserved.

72
Q

What happens in relation to voltage when two components are connected in parallel?

A

The voltage is the same for both components.

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