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Physics Paper 1 > Topic 2: Electricity > Flashcards

Topic 2: Electricity Flashcards

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1
Q

2.1

A

Current, Potential Difference and Resistance

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2
Q

What is electric current?

A

The flow of electrical charge

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3
Q

State the equation linking charge, current and time. Give the units for the quantities involved.

A
  • Q = I t
  • Charge (Coulombs), Current (Amperes), Time (Seconds)
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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
  1. Potential Difference (V)
  2. Resistance (R)
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6
Q

What equation should be used to calculate potential difference if current and resistance are known? State the units for all 3 quantities.

A
  • V = I R
  • Potential Difference (V), Current (A), Resistance (Ω)
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7
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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8
Q

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

A
  1. Lamps
  2. Diodes
  3. Thermistors
  4. Light Dependant Resistors (LDRs)
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9
Q

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

A
  • Resistance increases
  • Ions in metal have more energy, so vibrate more, causing more collisions with electrons as they flow through the metal, creating greater resistance to current flow
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10
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, preventing current flow
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11
Q

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

A

The thermistor’s resistance decreases.

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12
Q

Give two examples of when a thermistor may be used.

A
  1. In a thermostat to turn on below a certain temperature
  2. In a freezer to turn on a cooler when the temperature becomes too high
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13
Q

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

A

The LDR’s resistance increases

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14
Q

Give an application for a LDR.

A
  • Street lights often use LDRs
  • When light levels become too low, the light gains sufficient current to turn on
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15
Q

2.2

A

Series and Parallel Circuits

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16
Q

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

A
  1. Series (same loop)
  2. Parallel (adjacent loop)
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17
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
  • Parallel: P.D across each component is the same
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18
Q

If two resistors are connected in parallel, what can be said about their combined total resistance?

A

Their total resistance is less than the smallest of the two individual resistances.

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19
Q

If two resistors are connected in series, what can be said about their total resistance?

A

Their total combined resistance is equal to the sum of the two individual resistances.

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20
Q

Describe the current in a series circuit.

A

In a series circuit, the current is the same at all positions since the charge only has one path to flow through.

21
Q

Describe the current in a parallel circuit.

A

In a parallel circuit, the current is shared between the different branches. When the charge reaches a junction it splits.

22
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.

23
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.

24
Q

Why is it advantageous to connect lamps in parallel?

A

If one lamp blows, the rest will be unaffected and can still receive current (i.e. the circuit is still complete).

25
Q

2.3

A

Domestic Uses and Safety

26
Q

Is mains electricity an a.c. supply or a d.c. supply? What do each of these stand for?

A
  • Mains electricity is an a.c. supply
  • a.c. : Alternating Current
  • d.c. : Direct Current
27
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
28
Q

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

A
  • Frequency: 50 Hz
  • Voltage: 230V
29
Q

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

A
  1. Live wire
  2. Neutral wire
  3. Earth wire
30
Q

State the insulation colour used on the Earth wire.

A

Green and Yellow Stripes

31
Q

State the insulation colour used on the live wire

A

Brown

32
Q

State the insulation colour used on the Earth wire.

A

Blue

33
Q

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

A
  • Under normal circumstances, no current flows through the Earth wire
  • If a fault occurs in the appliance (such as a surge or the casing becoming live), current will flow to the ground
34
Q

What potential is the neutral wire at?

A

0 Volts

35
Q

State the potential difference between the live and earth wires.

A

230 Volts

36
Q

What is the purpose of the neutral wire?

A

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

37
Q

For metal appliances, where is the Earth wire connected to? Why?

A
  • Earth wire is connected to the metal casing of the appliance
  • If live wire becomes loose and touches the casing, the current will flow through the Earth wire, preventing electrocution
38
Q

2.4

A

Energy Transfers

39
Q

What two main factors does the amount of energy transferred by an appliance depend on?

A
  1. How long the appliance is being used for
  2. The power of the appliance
40
Q

What is the purpose of the National Grid?

A

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

41
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 the potential difference
42
Q

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

A
  • Step-down Transformers are used in connecting transmission cables to domestic buildings (like houses)
  • They decrease the potential difference
43
Q

Why do transmission lines transfer electricity at high potentials?

A
  • A high potential, results in a low current
  • The lower the current, the less energy that is wasted as heat
  • Therefore it is more efficient
44
Q

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

A
  • Lower potentials are safer for domestic use and reduces the likelihood of severe electrocution
  • Appliances are designed for 230V
45
Q

2.5

A

Static Electricity (Physics Only)

46
Q

Why can insulators become electrically charged when rubbed together?

A
  • Electrons are rubbed from one material onto the other
  • The material gaining electrons become negatively charged
  • The material losing electrons become equally positively charged
47
Q

What is an electric field?

A

A region in which a charged object will experience a non-contact electrical force.

48
Q

Describe the electric field around a charged particle.

A
  • Strongest closest to the object
  • Decreases in strength as you move away from the object
49
Q

In situation where sparks are unwanted, what precaution must be taken to prevent the build up of static charge?

A

Any surfaces that are rubbing against each other should be earthed to allow the charge to flow off the materials.

Physics Paper 1 (4 decks)

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