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Physics > 2. Electricity > Flashcards

2. Electricity Flashcards

1
Q

What is electric current?

A

The flow of electrical charge.

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2
Q

State the equation linking charge current and time.

A

Charge = Current x time Q=It

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3
Q

What is the unit of charge

A

Coulombs

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4
Q

What can be said about the value of current at any point in a single closed loop?

A

Current is the same at all points in a closed loop.

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5
Q

What two factors does the current in a circuit depend on?

A

Potential Difference (V), Resistance (R)

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6
Q

What equation should be used to calculate potential difference if current and resistance are known?

A

V = I R

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7
Q

What are the units for potential difference.

A

Volts

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8
Q

What are the units for current

A

Amps

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9
Q

What is the unit of resistance

A

Ohms

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10
Q

What is an Ohmic Conductor? State the condition required.

A

A conductor for which current and potential difference are directly proportional. Resistance remains constant as current changes. Temperature must be constant.

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11
Q

List four components for which resistance is not constant as current changes.

A

Lamps
Thermistor
Variable resistor
LDR

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12
Q

What happens to the resistance of a filament lamp as the temperature increases? Why?

A

Resistance increases. Ions in metal have more energy

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13
Q

What is different about current flow through a diode?

A

The current only flows in one direction. Resistance is very high in the other direction

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14
Q

State what happens to the resistance of a thermistor as temperature increases.

A

The thermistor’s resistance decreases.

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15
Q

Give an example of when a thermistor may be used.

A

In a thermostat to turn a heater on below a certain temperature

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16
Q

State what happens to the resistance of an LDR as light intensity decreases.

A

The LDR’s resistance increases.

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17
Q

Give an application for an LDR.

A

Street lights often use LDRs. When light levels become too low

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18
Q

What are the two ways that a component can be connected in a circuit?

A

Series (same loop)

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19
Q

How does the potential difference across two components vary when connected in series and parallel?

A

Series: Total P.D is shared between each component

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20
Q

If two resistors are connected in parallel

A

what can be said about their combined total resistance?

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21
Q

If two resistors are connected in series

A

what can be said about their total resistance?

22
Q

Describe the current in a series circuit.

A

In a series circuit all components are in 1 complete loop

23
Q

Describe the current in a parallel circuit.

A

In a parallel circuit the components are split across different loops in a circuit

24
Q

How should you connect an ammeter in a circuit to measure current?

A

Ammeters should be connected in series with the component that they are measuring current through.

25
Q

How should you connect a voltmeter in a circuit to measure potential difference?

A

Voltmeters should be connected in parallel to the component that they are measuring the potential difference of.

26
Q

Why is it advantageous to connect lamps in parallel?

A

If one lamp blows current can take an alternative route and the circuit will not be broken

27
Q

Is mains electricity an a.c. supply or a d.c. supply?

A

Mains electricity is an a.c. supply.

28
Q

What do a.c. and d.c. stand for?

A

a.c.: Alternating Current

29
Q

Define alternating current and direct current.

A

Alternating current: Current that continuously changes direction at a specific frequency. Direct current: One directional current flow.

30
Q

What is the frequency and voltage of the UK mains electricity supply?

A

Frequency: 50 Hz

31
Q

How many wires are usually in the cables connecting electrical appliances to the mains?

A

3 wires: Live wire, neutral wire earth wire

32
Q

State the insulation colour used on the Earth wire.

A

Green and Yellow Stripes

33
Q

State the insulation colour used on the live wire.

A

Brown

34
Q

State the insulation colour used on the neutral wire.

A

Blue

35
Q

Explain when the Earth wire does and doesn’t carry a current.

A

Under normal circumstances the earth does not carry a current, only when there is a fault does it carry current

36
Q

What potential is the neutral wire at?

A

0 Volts

37
Q

State the potential difference between the live and earth wires.

A

230 Volts

38
Q

What is the purpose of the neutral wire?

A

To complete the circuit by connecting the appliance back to the mains supply.

39
Q

State two equations for the power of a circuit.

A

P = I V, P = I squared R

40
Q

State an equation linking energy transferred power and time.

A

Energy transferred = power / time

41
Q

State an equation linking energy transferred

A

charge and potential difference.

42
Q

What two factors affect the energy transferred by an appliance?

A

How long the appliance is used for, how powerful it is

43
Q

Describe the energy transfers in a battery-powered torch.

A

Battery converts chemical energy into electrical energy. Bulb converts electrical energy into light and waste energy in the form of heating.

44
Q

Describe the energy transfers in a battery-powered motor.

A

Battery converts chemical energy into electrical energy. Motor converts electrical energy into kinetic energy and waste energy in the form of heating.

45
Q

What three things determine the power of a circuit device?

A

Potential difference, current, resistance

46
Q

What is the purpose of the National Grid?

A

To link power stations to consumers so that they have access to electricity.

47
Q

What are the two types of transformers used in the National Grid?

A

Step-Up Transformers, step down transformers

48
Q

Where are step-up transformers found in the National Grid? What do they do?

A

Step-Up Transformers are used when connecting power stations to transmission cables. They increase potential difference.

49
Q

Where are step-down transformers found in the National Grid? What do they do?

A

Step-Down Transformers are used when connecting transmission cables to domestic buildings. They decrease potential difference.

50
Q

Why do transmission lines transfer electricity at high potentials?

A

A high potential results in a low current. The lower the current therefore less energy lost as heat.

51
Q

Why does the potential need to be decreased between transmission lines and houses?

A

Lower potentials are safer for domestic use and reduce the likelihood of severe electrocution. Appliances are designed for 230V.

Physics (7 decks)

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