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Year 11 GCSE Physics > Electricity > Flashcards

Electricity Flashcards

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1
Q

What is a conductor?

A

A conductor is a material which allows electric current to pass through it.

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2
Q

Why are metals (and as an extension some non-metals) good conductors?

A

In a conductor some electrons can move freely from atom to atom. These electrons are known as free electrons or delocalised electrons. There are large numbers of free electrons in conductors.

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3
Q

What is an insulator?

A

An insulator is a material which does not allow electric current to pass through it.

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4
Q

Why is it that insulators do not conduct electricity well?

A

The electrons within an insulator are tightly bound to their atoms - they do not contain a large enough number of free electrons.

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5
Q

How can you test materials to see whether or not they are a conductor or an insulator?

Draw the circuit diagram and then describe the method.

A

METHOD FOR TESTING:

  1. Test the circuit first by checking if it works when there is no gap.
  2. Then insert the material you want to test into the gap in your circuit. (Between the two wires)
  3. If the bulb does light the material is a conductor.

4.. If it does not light the material is an insulator.

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6
Q

List some insulators.

A

Wood, slate, rubber, perspex and marble.

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7
Q

List some conductors.

A

Steel, aluminium, brass, lead and copper.

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8
Q

List some non-metal conductors.

A

Water and graphite.

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9
Q

What is an electric current?

A

An electric current is a flow of electric charge or charge carriers.

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10
Q

What is conventional current?

A

Conventional current flows from the positive terminal of the power source to the negative terminal. Conventional current is simply referred to as current.

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11
Q

What is electron flow?

A

Electrons flow in the circuit from the negative terminal of the power source to the positive terminal.

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12
Q

Why do electrons in actuality move from the negative terminal of the power source to the positive terminal?

A

Negatively charged electrons are repelled from the negative terminal of the battery and are then attracted to the positive terminal of the battery.

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13
Q

Which end of the battery in a circuit diagram is the positive end?

A

The long side of the battery (in the circuit diagram) is the positive end.

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14
Q

What is the quantitive relationship between current, charge and time?

A

charge = current multiplied by time

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15
Q

What is charge measured in?

A

Charge is measured in Coulombs (C).

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16
Q

What is the unit for electric current?

A

The unit for electric current is the Ampere or the Amp (A).

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17
Q

What is one coulomb of charge worth in amps and seconds?

A

Once Coulomb of charge is the charge passing a point in a circuit when one Amp flows for one second.

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18
Q

How many electrons are in one Coulomb of charge?

A

One coulomb of charge contains 6.25 X 10¹⁸ electrons.

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19
Q

What are the symbols for Charge = Current multiplied by time?

A

Q = It

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20
Q

What is the formula for charge?

A

Q = It

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21
Q

What is the formula for time (Q = It)

A

t - Q/I

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22
Q

What is the formula for Current (Q = It)

A

I = Q/t

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23
Q

Draw a switch.

A
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24
Q

Draw a resistor.

A
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25
Q

Draw a voltmeter.

A
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26
Q

Draw a cell.

A
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27
Q

Draw a variable resistor.

A
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28
Q

Draw an ammeter.

A
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29
Q

Draw a battery.

A
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30
Q

Draw a fuse.

A
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31
Q

Draw a lamp.

A
32
Q

What two things are integral for a circuit to work?

A
  1. You circuit must be complete without any gaps.
  2. There must be no short circuits.

(If you can go from one battery terminal to the other WITHOUT passing through any components there is a short circuit)

33
Q

In a circuit diagram, there are two lamps connected in series. If one lamp breaks what will happen to the other one?

In another circuit diagram, there are two lamps connected in parallel. If one lamp breaks what will happen to the other one?

A

In the series circuit the other lamp will turn off.

In the parallel circuit the other lamp will continue to emit light.

34
Q

What is current measured with? How do you use it?

A

Current is measured with an ammeter. The ammeter is connected in series with an electrical device. It should be connected with the correct polarity either side (negative or positive charge).

35
Q

What are the properties of a series circuit?

A

The current is the same everywhere in a series circuit.

The voltage from the battery is split across the components in the circuit.

36
Q

What are the properties of a parallel circuit?

A

The current is split up through the branches of a parallel circuit. The total current in the circuit is equal to the sum of the currents in the individual branches.

The Voltage is the same across each branch and it has the same value as the voltage of the battery. However, if there is more than one component in one branch the voltage will split up between the components within that branch.

37
Q

How do you measure with an ammeter?

A

You need to connect the ammeter to the circuit in series.

38
Q

How do you measure with a voltmeter?

A

You connect the voltmeter in parallel in the circuit.

39
Q

What is resistance?

A

Resistance is the opposition to the flow of current in a circuit.

It is defined as the ratio of voltage to current (i.e. R = V/I)

40
Q

What is Ohm’s Law in full?

A

Ohm’s Law is as following:

The current through a conductor, which obeys Ohm’s Laws, is directly proportional to the voltage across it provided the temperature remains constant.

41
Q

What is the equation for Ohm’s Law?

A

Voltage (V) = Current (A) X Resistance (Ω)

OR

V = IR

42
Q

How do you rearrange V = IR to calculate the current?

A

I = V/R

43
Q

How do you rearrange V = IR to calculate the resistance?

A

R = V/I

44
Q

How do you find the total voltage in a series circuit?

A

You find the sum of the separate voltages throughout the circuit. Once added you have the total voltage coming from the battery.

45
Q

How do you find the total current in a parallel circuit?

A

You add up the total current of each parallel branch to get the total current.

46
Q

How does voltage behave in a parallel circuit?

A

Voltage is the same across all parallel sections.

The voltage will also split itself up between components in the same branch.

47
Q

How is resistance affected by the size of current?

A

As current increases so does resistance.

48
Q

What is the relationship between the temperature of a filament bulb and the resistance?

A

As current flows through the filament bulb, the temperature of the bulb increases. This means means the resistance also increases.

49
Q

Why is the filament bulb a non-ohmic conductor?

A

As the temperature of the bulb increases (due to the circuit’s current) the heat energy is transferred to the filament’s ions. The ions gain kinetic energy and vibrate more. This causes collisions between the circuit’s free electrons and the filament’s vibrating ions.

These collisions decrease electron flow speed thus increasing resistance - making V=IR disproportional and the conductor non-ohmic.

If you were to plot the current and voltage readings on a filament bulb you would get a steep rising curve starting from (0,0).

50
Q

How can you find the total resistance of two or more resistors connected in series?

A

Total Resistance = Resistor 1 + Resistor 2 + Resistor 3 + etc…

51
Q

How can you find the total resistance of two or more resistors connected in parallel?

A

1/Resistance Total = 1/Resistor 1 + 1/Resistor 2 + 1/Resistor 3 + 1/etc

You then take this answer (1/Resistance Total) and inverse it (find the reciprocal) equalling the Resistance Total.

52
Q

Why is there resistance in a wire?

A

The resistance of a metal wire is due to collisions between the delocalised (free) electrons and the vibrating ions of the metal wire the electrons are flowing through.

53
Q

What is the relationship between the length of a wire and its resistance?

A

As the length of the wire increases so too does the number of vibrating ions (that the electrons need to move past). Hence there are more collisions occurring between free electrons and the vibrating ions, in other words is a greater opposition to current flow i.e. a greater resistance.

54
Q

What is the relationship between the CSA (Cross-Sectional Area) of the Wire and resistance?

What is the graph produced from an investigation of the relationship of the CSA of a wire and its resistance?

What can we infer from this graph? How can we prove this inference?

Give an explanation to why this happens?

A

As the cross-sectional area (CSA) of the wire increases, its resistance decreases. The graph produced is a downward flattening curve. This graph shape suggests inverse proportion between the CSA and the resistance of the wire.

If you were to plot a graph of 1/CSA (or the inverse of the CSA) against resistance a straight line graph through the origin is produced. This tells us that the resistance is directly proportional to 1/CSA. This is usually referred to as inverse proportion (between CSA and resistance), in other words: the cross-sectional area of the wire is inversely proportional to its resistance.

As the cross-sectional area increases, so does the space available for free electrons to move through the wire. Hence there will be fewer collisions between the vibrating ions in the wire and the free electrons; i.e. less resistance.

Bigger CSA = Less resistance
Smaller CSA = Bigger resistance

55
Q

What is the equation for the relationship between the length of a wire and its resistance?

A

R = kL

R/L = constant

Hence the value for any given wire the value R/L will always be the same. (Given that the material is the same between the wires being compared).

i.e. Resistance 1/Length 1 = Resistance 2/Length 2 = Resistance 3/Length 3 = etc…

56
Q

What is the equation for the relationship between the cross-sectional area of a wire and its resistance?

A

R times CSA = constant

R = constant/CSA

Hence for any given wire the value R times CSA will always be the same (Given that the material is the same between the wires being compared).

i.e. Resistance 1 X CSA 1 = Resistance 2 X CSA 2 = Resistance 3 X CSA 3 = etc…

57
Q

What are the factors that affect resistance?

A

The resistance of a conductor depends on several factors:

Length - increasing the length of a wire increases its resistance; decreasing the length of a wire decreases its resistance;

Cross-sectional area - increasing the thickness (i.e. diameter) and therefore increasing the cross-sectional area of a wire decreases its resistance. Conversely, decreasing the thickness and therefore decreasing the cross-sectional area of a wire increases its resistance.

Material - Different materials have different resistances e.g. a copper wire has less resistance than a nichrome wire with the same dimensions. This occurs because different materials have different number of free electrons per mm³ - a material with low resistance will have a high number of free electrons per mm³.

Temperature - for metal conductors, resistance increases with temperature.

58
Q

Why do different materials have different resistances?

A

Different materials have different resistances e.g. a copper wire has less resistance than a nichrome wire with the same dimensions. This occurs because different materials have different number of free electrons per mm³ - a material with low resistance will have a high number of free electrons per mm³.

59
Q

Why does electricity heat up wires?

A

A metallic conductor has a large number of free electrons in it. When a potential difference is applied across the ends of a metallic wire, the free electrons begin to drift from the low potential to the high potential region. These electrons collide with the positive ions (the atoms which have lost electrons). In these collisions, the energy of the electrons is transferred to the positive ions and they begin to vibrate more violently. As a result, heat is produced. The greater the number of electrons flowing per second, the greater will be the rate of collision and hence more heat is produced.

60
Q

What are the equations for Power?

A

Power (W) = Energy changed (J)/ Time (Seconds)

P = E/t

Power (W) = Current (A) X Voltage (V)

P = IV

61
Q

How do we calculate kilowatt-hours?

A

Number of Units used (kWh) = Power (kW) X time (Hours)

62
Q

How do you calculate the total cost using kWh and the price of one unit?

For example work out the price of 3 kWh if a kWh unit of electricity cost 15p per hour?

A

Total cost = Number of kilowatt hour units X price of 1 unit

3 kWh X 15p = 45p

63
Q

What are the properties of a one-way switch?

A

One-way switches are basically make or break switches, because when it is turned on (closed), the two terminals are connected, and when it is turned off (opened), the contact between the two terminals are broken.

64
Q

Where should switches be placed in a circuit?

A

All switches must be in the live wire. If they were in the neutral wire the appliance and power sockets would still be live when the switches are off.

The live side of the circuit is the space in between the positive terminal of the battery and the nearest component. The switch needs to be right beside the positive terminal of the battery.

65
Q

What is a two-way switch?

What are its properties and how does it work?

Draw a two-way switch.

A

A two way switch is used to control the same component from two different locations.

There is defined position for the off or on states when used as flipping either switch can turn the light on or off. You would find two-way switches at staircases (at the top and bottom) and long corridors (at each end)

66
Q

Why do appliances have plugs fitted and wired already?

A

Plugs now come pre-fitted with appliances and pre-wired. This was done to reduce the number of accidents occurring whenever people try and wire plugs themselves.

67
Q

What are the types of wire in a mains electricity cable?

How can they be identified and what do they do?

A

Each wire is colour coded so it can be identified.

The Brown Wire in a Three Pin Plug is the Live wire. It is held at a voltage of 230 V (that is the UK standard) and provides current to appliances. This is the dangerous wire.

The Blue Wire is the neutral wire. It completes the circuit.

The Green and Yellow Striped Wire is the Earth Wire. It is a safety wire to stop the appliance becoming live. It connects the metal frame of the appliance to the Earth.

68
Q

Where do each of the types of wire connect to in a Three Pin Plug?

A

The bLue wire goes to the Left pin.

The bRown wire goes to the Right pin.

The sTriped wire goes to the Top pin.

The second letters of each the wires (Blue, Brown and Striped) can help remind you where each of the wires go to in the Three Pin Plug.

69
Q

Where is the fuse located in a Three Pin Plug?

A

The fuse comes in between the Live wire and its pin. (The right pin)

70
Q

What are fuses?

Where are fuses placed in the circuit?

A

A fuse is a short length of thin wire made from a material which has a low melting point. When the fuse overheats, due to a fault in the circuit, it melts and the circuit is broken.

The fuse melts and breaks the circuit when the current though it is more than a certain value.

Fuses are always placed in the live wire.

71
Q

What value should the fuse be corresponding to the circuit it is in?

A

The value of the fuse should be just above the normal current needed by the appliance. If the normal current going through a circuit is 4A, the fuse should then be 5A.

72
Q

How does the Earth Wire “Earth” the appliance when there is a fault in the electrical appliance?

A

If a fault develops in fault develops in an electrical appliance and the live wire is able to come into contact with the metal case of the appliance, then touching that metal case would possibly receive a fatal shock as current will pass through their body to Earth.

The Earth Wire and fuse work together to prevent this from happening.

The Earth Wire provides a low resistance route allowing the current to reach Earth through the wire rather than person.

As a results of the low resistance, current increases and melts the fuse in the appliance, as a result there is a break in the circuit and the circuit needs to be fixed again before reusing.

73
Q

What is “Double Insulation”? Draw the symbol for double insulation.

A

Appliances such as hairdryers and vacuum cleaners are normally double insulated. These appliances only have a live and neutral wire connecting them to the mains supply. THEY DO NO HAVE AN EARTH WIRE. To protect the user from electric shock these appliances are completely encase in an insulated plastic case so that people cannot come into contact with any live components.

74
Q

What is the equation for energy?

A

E (J) = P (W) times t (Seconds)

75
Q

What is the equation for time using energy and power?

A

t (Seconds) = E (J)/ P(W)

Year 11 GCSE Physics (2 decks)

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