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Physics > Topic 2: Electricity > Flashcards

Topic 2: Electricity Flashcards

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1
Q

What is current?

A

The flow of electrical charge

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2
Q

What must a circuit contain for current to flow?

A

A source of potential difference

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3
Q

What is the rule linking resistance and current?

A

The greater the resistance across a component, the smaller the current

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4
Q

Explain in terms of current, pd and resistance what happens in an ohmic conductor [2]

A
  1. Current is directly proportional to the pd across the resistor
  2. Therefore, the resistance remains constant as the current changes
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5
Q

Explain in terms of current, pd and resistance what happens in a filament lamp [3]

A
  1. As the current increases, the temperature of the filament increases
  2. So the resistance increases
  3. This means less current can flow per unit of pd
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6
Q

Explain in terms of current, pd and resistance what happens in a diode [2]

A
  1. The current only flows in one direction through a diode
  2. The diode has a very high resistance in the reverse direction
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7
Q

In an LDR, what happens to the resistance as light intensity increases?

A

Resistance decreases

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8
Q

Everyday application of LDRs

A

Automatic night lights

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9
Q

In a thermistor, what happens to the resistance as temperature increases?

A

Resistance decreases

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10
Q

Everyday applications of thermistors

A

Thermostats

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11
Q

Rules of series circuits [3]

A
  1. The p.d is shared
  2. The current is the same everywhere
  3. The resistance adds up
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12
Q

Rules of parallel circuits [4]

A
  1. The p.d is the same everywhere
  2. The current is shared by each loop
  3. Adding a resistor reduces the total resistance
  4. Smaller than the smallest resistance of a branch
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13
Q

Is mains electricty an ac or dc supply?

A

ac

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14
Q

What is happening to the current in ac supplies?

A

Current is constantly changing direction

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15
Q

What causes alternating currents?

A

Alternating voltages in which the positive and negative ends keep alternating

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16
Q

What is the voltage of mains electricity?

A

230 V

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17
Q

What is the frequency of mains electricity?

A

50 Hz

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18
Q

What 2 things use direct current?

A

Cells and batteries

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19
Q

What is happening to the current in dc supplies?

A

Current is always flowing in the same direction

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20
Q

What causes direct currents?

A

Direct voltages

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21
Q

What is the name of the cable that most electrical appliances are connected to the mains supply by?

A

Three-core cable

22
Q

What metal is used inside wires in three-core cables?

A

Copper

23
Q

Why is each wire in a three-core cable colour coded?

A

For easy identification

24
Q

What colour is the neutral wire?

A

Blue

25
Q

What colour is the live wire?

A

Brown

26
Q

What colour is the earth wire?

A

Green and yellow stripes

27
Q

What is the job of the neutral wire?

A

It completes the circuit

28
Q

What is the job of the live wire?

A

Carries the alternating pd from the mains supply

29
Q

What is the job of the earth wire?

A

A safety wire to stop the appliance becoming live

30
Q

What is the pd of the neutral wire?

A

0 V

31
Q

What is the pd of the live wire?

A

230 V

32
Q

What is the pd of the earth wire?

A

0 V

33
Q

When would the earth wire carry current?

A

If there was a fault

34
Q

Describe what would happen if a person touched a live wire [3]

A
  1. Your body is at 0 V
  2. Therefore, if you touched a live wire, a large pd would be produced across your body and a current would flow through you
  3. This would cause a large electric shock that could injure or kill you
35
Q

Why is there still a danger of an electric shock even when an appliance has been turned off? [2]

A
  1. There is still a pd in the live wire
  2. So if you made contact with the live wire you would provide a link between the supply and earth and a current would flow through you
36
Q

Why is any connection between the live wire and earth dangerous? [3]

A
  1. The link could create a low resistance path to earth
  2. A huge current would flow
  3. Which could result in a fire
37
Q

What is potential difference?

A

The energy transferred per charge passed

38
Q

What 2 things does the energy transferred by an appliance depend on?

A
  1. How long the appliance is on for
  2. Its power
39
Q

What does it mean if an appliance has a higher power rating?

A

It uses more electricity in a given time

40
Q

What does power rating mean?

A

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

41
Q

What does the National Grid link?

A

Power stations to consumers

42
Q

What do step-up transformers do?

A

Increase the pd and causing the current to decrease

43
Q

What do step-down transformers do?

A

Decrease the pd causing the current to increase

44
Q

Why is the National Grid an efficient way to transfer energy? [4]

A
  1. The National Grid distributes electricity at a high pd and a low current
  2. A high pd means that it can distribute lots of power per second
  3. Using a low current reduces energy losses
  4. Which makes the National Grid efficient at transferring energy
45
Q

What happens when two insulating materials are rubbed together?

A

Static charge will build up on both objects

46
Q

If a polythene rod and cloth are rubbed together, which way will the electrons be transferred?

A

To the cloth

47
Q

If an acetate rod and cloth are rubbed together, which way will the electrons be transferred?

A

To the rod

48
Q

Explain how sparks are formed [4]

A
  1. Size of charge on object increase
  2. Potential difference between the object and earth increases
  3. Electrons can jump across the gap
  4. This is a spark
49
Q

How can cars build up charge?

A

Wind blowing on them can transfer electrons to the metal frame

50
Q

Which way do field lines go?

A

From positive to negative

51
Q

How can sparking be explained by electric fields? [3]

A
  1. A strong enough electric field can cause electrons to be removed from air particles (ionisation)
  2. This makes air conductive so it can carry current
  3. This is a spark

Physics (8 decks)

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