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Physics > Topic 2: Electricity > Flashcards

Topic 2: Electricity Flashcards

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?

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?

25
What colour is the live wire?
Brown
26
What colour is the earth wire?
Green and yellow stripes
27
What is the job of the neutral wire?
It completes the circuit
28
What is the job of the live wire?
Carries the alternating pd from the mains supply
29
What is the job of the earth wire?
A safety wire to stop the appliance becoming live
30
What is the pd of the neutral wire?
0 V
31
What is the pd of the live wire?
230 V
32
What is the pd of the earth wire?
0 V
33
When would the earth wire carry current?
If there was a fault
34
Describe what would happen if a person touched a live wire [3]
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
Why is there still a danger of an electric shock even when an appliance has been turned off? [2]
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
Why is any connection between the live wire and earth dangerous? [3]
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
What is potential difference?
The energy transferred per charge passed
38
What 2 things does the energy transferred by an appliance depend on?
1. How long the appliance is on for 2. Its power
39
What does it mean if an appliance has a higher power rating?
It uses more electricity in a given time
40
What does power rating mean?
The maximum amount of energy transferred between stores per second when the appliance is in use
41
What does the National Grid link?
Power stations to consumers
42
What do step-up transformers do?
Increase the pd and causing the current to decrease
43
What do step-down transformers do?
Decrease the pd causing the current to increase
44
Why is the National Grid an efficient way to transfer energy? [4]
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
What happens when two insulating materials are rubbed together?
Static charge will build up on both objects
46
If a polythene rod and cloth are rubbed together, which way will the electrons be transferred?
To the cloth
47
If an acetate rod and cloth are rubbed together, which way will the electrons be transferred?
To the rod
48
Explain how sparks are formed [4]
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
How can cars build up charge?
Wind blowing on them can transfer electrons to the metal frame
50
Which way do field lines go?
From positive to negative
51
How can sparking be explained by electric fields? [3]
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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