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GCSE Physics > Electricity > Flashcards

Electricity Flashcards

1
Q

What is an electric current?

A

A flow of electric charge.

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2
Q

What is the equation linking charge, current and time?

A

charge = current x time

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3
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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4
Q

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

A
  1. Potential Difference (V)
  2. Resistance (R)
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5
Q

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

A

V = I R
Potential Difference (V), = Current (A) x Resistance (Ω)

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6
Q

What is an ‘Ohmic Conductor’?

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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7
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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8
Q

What happens to the resistance of a filament lamps 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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9
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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10
Q

what happens to the resistance of a thermistor as temperature increases?

A

The thermistor’s resistance decreases.

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11
Q

Give two examples of when a thermistor may be used

A
  1. In a thermostat to turn a heater on below a certain temperature
  2. In a freezer to turn on a cooler when the temperature becomes too high
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12
Q

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

A

The LDR’s resistance increases.

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13
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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14
Q

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

A
  1. Series (same loop)
  2. Parallel (adjacent loop)
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15
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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16
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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17
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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18
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.

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19
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.

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20
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.

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21
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.

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22
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).

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23
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

24
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

25
Q

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

A

● Frequency: 50 Hz
● Voltage: 230V

26
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
27
Q

State the insulation colour used on the Earth wire.

A

Green and yellow stripes

28
Q

State the insulation colour used on the live wire.

A

brown

29
Q

State the insulation colour used on the neutral wire.

A

Blue

30
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

31
Q

What potential is the neutral wire at?

A

0 volts

32
Q

State the potential difference between the live and earth wires.

A

230 volts

33
Q

What is the purpose of the neutral wire?

A

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

34
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

35
Q

State two equations for the power of a circuit. Give appropriate units.

A

P = I V P = I² R
Power (Watts), Current (Amperes) Potential Difference (Volts), Resistance (Ohms)

36
Q

State an equation linking energy transferred, power and time. Give appropriate units.

A

E = P t
Energy (Joules), Power (Watts), Time (Seconds)

37
Q

State an equation linking energy transferred, change flow and potential difference. Give appropriate units.

A

E = QV
Energy (joules), charge (coulombs), potential difference (volts)

38
Q

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

A

How long the appliance is being used for
- The power of the appliance

39
Q

Describe the energy transfers in a battery powered torch

A

● Battery converts chemical energy into electrical energy
● Bulb converts electrical energy into light as well as waste energy in the form of heating

40
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 as well as waste energy in the form of heating due to friction

41
Q

What three things determine the power of a circuit device?

A
  • the potential difference across the circuit
  • the current through the circuit
  • the amount of energy transferred in a given time
42
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.

43
Q

What are the two types of transformers used in the national grid?

A

Step-up transformers and step-down transformers

44
Q

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

A

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

45
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

46
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

47
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

48
Q

What can happen when insulating materials are rubbed together?

A

They can become (statically) electrically charged.

49
Q

What happens when two electrically charged objects are bought close together?

A

They exert a force on each other

50
Q

What happens when two identically charged objects are brought close together?

A

They exert a repulsive force on each other and repel.

51
Q

What happens when two oppositely charged objects are bought close together?

A

They exert an attractive force on each other and attract

52
Q

Give an example of non-contact force

A

The repulsive or attractive force acting between two electrically charged objects.

53
Q

What is an electric field?

A

a region around a charged particle or object within which a force would be exerted on other charged particles or objects.

54
Q

Where can electric fields be found?

A

Surrounding any charged object.

55
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

56
Q

What happens to the force between two charged objects when they are moved closer together?

A

The force between them becomes stronger as the separation reduces.

57
Q

In situations 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.

GCSE Physics (8 decks)

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