Physics F Tier > 2. Electricity > Flashcards

2. Electricity Flashcards

(57 cards)

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1
Q

What is electric current

A

The flow of electric charge

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2
Q

What is current measured in

A

Amperes A

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3
Q

What is electric charge measured in

A

Coulombs C

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4
Q

What is the equation linking charge current and time

A

Q = I t

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5
Q

Units for Q = I t

A

Q in coulombs C I in amperes A t in seconds s

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6
Q

What is potential difference voltage

A

The energy transferred per unit charge between two points

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7
Q

What is the equation linking potential difference energy and charge

A

V = W / Q

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8
Q

Units for V = W / Q

A

V in volts V W in joules J Q in coulombs C

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9
Q

What is resistance

A

A measure of how much a component opposes the flow of current

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10
Q

What is the equation linking potential difference current and resistance

A

V = I R

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11
Q

Units for V = I R

A

V in volts V I in amperes A R in ohms Ω

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12
Q

What is Ohms law

A

For a fixed temperature current through an ohmic conductor is directly proportional to potential difference

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13
Q

What happens to a filament lamps resistance as current increases

A

Resistance increases because the lamp gets hotter

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14
Q

How does a diode behave

A

It allows current to flow in one direction only very high resistance in reverse

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15
Q

What happens to a thermistors resistance as temperature increases

A

Resistance decreases

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16
Q

How does an LDRs resistance change with light intensity

A

Resistance decreases as light intensity increases

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17
Q

In a series circuit what is current like through each component

A

Same through each component

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18
Q

What happens to total potential difference in a series circuit

A

Shared between components

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19
Q

What happens when you add more resistors in series

A

Total resistance increases R total = R₁ + R₂ + …

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20
Q

In a parallel circuit what is potential difference like across each branch

A

Same across each branch

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21
Q

What is total current in a parallel circuit

A

Sum of the currents in the separate branches

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22
Q

What happens when you add more resistors in parallel

A

Total resistance decreases more paths for current

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23
Q

What is electrical power

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A

The rate of energy transfer in a circuit

24
Q

What are the equations for electrical power

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A

P = V I and P = I² R

25
Units for P = V I and P = I² R
P in watts W V in volts V I in amperes A R in ohms Ω
26
What is the equation linking energy charge and potential difference
E = Q V
27
Units for E = Q V
E in joules J Q in coulombs C V in volts V
28
What is the equation linking energy power and time
E = P t
29
Units for E = P t
E in joules J P in watts W t in seconds s
30
What does electrical power depend on
Potential difference and current
31
What is meant by efficiency
Useful energy or power output ÷ total energy or power input
32
What is direct current d c
A current that flows in one constant direction such as from a cell or battery
33
What is alternating current a c
A current that repeatedly changes direction as in mains electricity
34
What is the frequency and potential difference of UK mains supply
50 Hz and 230 V
35
What are the three wires in a mains cable
Live brown neutral blue earth green yellow
36
What is the potential of the live wire
About 230 V with respect to earth
37
What is the potential of the neutral wire
Approximately 0 V near earth potential
38
What is the purpose of the earth wire
Safety provides a low resistance path to the ground if the case becomes live
39
What happens if the live wire touches a metal case without an earth wire
The case could become live and cause electric shock
40
What is the function of a fuse
To break the circuit if current becomes too large melts
41
What is the function of the cable grip
Holds the cable securely in the plug
42
What happens when a fuse melts
It disconnects the live supply stopping current flow
43
Why does a resistor get hot when current flows
Electrical energy is transferred to thermal energy due to resistance I²R heating
44
Why are high currents in cables undesirable
They cause greater energy loss as heat P = I²R
45
How can power losses in transmission be reduced
Use high potential difference and low current for efficiency
46
What does the National Grid do
Transfers electrical energy from power stations to consumers
47
Why are larger and hotter power stations more efficient
Higher operating temperatures increase efficiency of energy transfer
48
What are the advantages of the National Grid system
Efficient long distance transfer and flexible distribution of electricity
49
What type of current is used in the National Grid
Alternating current a c to allow easy voltage transformation
50
What does an oscilloscope trace for a c look like
A repeating waveform crossing zero volts
51
What does an oscilloscope trace for d c look like
A straight line constant voltage
52
Why is the earth wire important in appliances with metal cases
It prevents electric shock by conducting fault current safely to earth
53
Why is the fuse connected to the live wire
So it disconnects the appliance from the high voltage supply if the current is too large
54
What happens when you touch a live wire
Large potential difference across the body causes a current that can be fatal
55
What does resistance depend on
Material length thickness and temperature of the conductor
56
Why is a parallel circuit often used in homes
Each device can be controlled independently and receives full mains voltage
57
Why is total resistance in a parallel circuit less than the smallest resistor
More current paths reduce total opposition to flow
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