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Physics Paper 1 > Electricity > Flashcards

Electricity Flashcards

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1
Q

Rules for drawing circuits:

A
  1. Straight lines for wires
  2. Battery should be on top
  3. No components on corners
  4. When drawing a cell/ battery, the long line represents the positive side and the short side represents the negative side.
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2
Q

What does a closed circuit need for an electrical charge to flow through it?

A

The circuit must contain a source of potential difference.

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3
Q

What is electrical current?

A

The flow of electric charge, the size of it is the rate of flow of electrical charge (measured in amps).

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4
Q

What is the value of current like in a single closed circuit?

A

It has the same value as it has no where else to go so it’s the same at all points in the loop.

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5
Q

What does the current (I) through a current depend on?

A

Both the resistance (R) and the potential difference (V) across the component.

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6
Q

The greater the resistance of the component…

A

The smaller the current for a given potential difference across the component.

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7
Q

What is the resistance of a component?

A

A measure of how it resists the flow of charge.

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8
Q

The higher the resistance…

A

The more difficult it is for charge to flow

The lower the current

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9
Q

What is resistance measure in?

A

Ohms

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10
Q

What is potential difference/ voltage?

A

Tells us the difference in electrical potential from one point in a circuit to another.

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11
Q

The bigger the potential difference across a component…

A
  • The greater the flow of charge through the component.

- The bigger the current.

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12
Q

What is potential difference measured in?

A

Volts using a voltmeter.

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13
Q

What are potential difference- current (IV) graphs used to show?

A

The relationship between the potential difference (voltage) and current for any component.

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14
Q

What does a straight line through the origin of an IV graph indicate?

A

The voltage and current are directly proportional. (The resistance is constant)

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15
Q

What does a steep IV graph gradient indicate?

A

Low resistance as a large current will flow for a small potential difference.

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16
Q

What does a shallow gradient of an IV graph indicate?

A

A high resistance as a large potential difference is needed to produce a small current.

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17
Q

How do resistors sometimes result in a non-linear graph?

A

The value of R is not constant but changes as the value of the current changes.

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18
Q

What is the resistance of a thermistor like?

A

The resistance of a thermistor decreases as the temperature increases, this makes the useful in circuits where temperature control/response is required.

E.g. a thermistor could be used in a circuit for a thermostat that turns a heater off at a particular temperature or an indicator light that turns on when a system is over heating.

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19
Q

What is the resistance of an LDR like?

A

The resistance of an LDR decreases as light intensity decreases. Theo’s makes them useful where automatic light control/detection is needed.

E.g. in duck till dawn garden lights/street lights and in cameras/phones to determine if a flash is needed.

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20
Q

What are electrical components either joined in?

A

Series or parallel

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21
Q

Components connected in series:

A
  • Current- Same through each component
  • Total PD- Sum of PDs/ voltages across each component (the PD of the power supply is shaped)
  • Total resistance- The sum of the resistance of each component
22
Q

Components connected in parallel:

A
  • Total current through the whole circuit is the sum of the currents through the separate components.
  • PD across each component is the same
  • Total resistance of two resistors is less than the resistance of the smallest individual resistor.
23
Q

What is a direct current?

A

Has a PD that is always positive/ negative- the current direction is constant.
This type of current is supplied by cells/batteries.

24
Q

What is Alternating current?

A

Current that constantly changes direction.

25
Q

What type of current is mains electricity?

A

AC

It is 230v and changes direction 50 times a second- it has a frequency of 50Hz

26
Q

How are most electrical appliances connected to mains?

A

Using a 3 core cable.

27
Q

What is the brown wire?

A

The live wire

28
Q

What is the blue wire?

A

Neutral wire

29
Q

What is the green and yellow striped wire?

A

Earth wire

30
Q

What does the live wire do?

A

Carries alternating PD from the supply

31
Q

What does the neutral wire do?

A

Completes the circuit

32
Q

What does the earth wire do?

A

Safety wire to stop the appliance becoming live, carries any dangerously high current away.

33
Q

What happens during operation when current runs through a 3 core cable?

A
  • Pd causes current to flow through live wire and neutral wires.
  • live wire carries the alternating potential from the supply.
  • The neutral wire completes the circuit.
  • Current will inky flow in the earth wire I’d there is a fault connecting it to a non-zero potential.
34
Q

How can touching the live wire be dangerous?

A

It can create a large PD across the body and result in a large current flowing through the body.

35
Q

How can the live wire be dangerous if a switch in the circuit is open?

A

A TV might be switched off but still plugged in and switch led on at the wall, the live wire between the wall and switch is still at an alternating potential, all it needs is a path for the electricity to flow, this path could be provided by a cable exposing the live wire. If someone then touches the live wire, creating a PD from the live to earth causing current to flow, they’ll get an electric shock.

36
Q

What is power?

A

The rate at which energy is transferred or work is done.

37
Q

What is an energy transfer of 1J per second equal to?

A

1W of power

E.g.
if two kettles are used to bring the same amount of water to the boil and one takes time, it is because it has a higher power.

38
Q

What is efficiency like in an energy transfer?

A

Is the ratio of useful energy out to total energy in:

An efficiency of 50% means half the energy is wasted an half of it is useful.

39
Q

How do you increase the efficient of an energy transfer?

A

The amount of wasted energy needs to be reduced.

40
Q

What are electrical appliances designed to do?

A

To bring about energy transfers, the amount of energy in an appliance depends on how long the appliances is switched on for and the power of the appliance.

41
Q

What does flowing charge have to overcome?

A

Resistance which requires energy, therefore:

  • Work is down when charge flows
  • The amount of work done depends on the amount of charge that flows and the potential difference.
42
Q

What does the type and amount of energy transferred between stores depend on?

A

The appliance

43
Q

What is the national grid?

A

A system of cables and transformers linking power stations to consumers.

44
Q

How is electrical power transferred from power stations to consumers?

A 
Using the national grid-
Power station (25000v) 
Step up transformer 
Transmission cables (400000v) 
Step down transformer
Consumer (230v)
45
Q

What does a power station transfer energy supply into?

A

Electrical energy

46
Q

Why is using a small number of large power station more efficient than building many small local power stations?

A

Large stations can be made more efficient because most power plants use steam turbines which are more efficient at higher steam temperatures and the bigger the plant, the higher the steam temperature.

47
Q

What do step up transformers do?

A

The transformers increase the PD from the power station to the transmission cables. This reduces the current and therefore reduces the heating effect caused by current flowing in the transmission cables. Reducing the heating affect reduces energy loss so makes the transmission more efficient.

48
Q

What do transmission cables do?

A

Transfer electricity.

49
Q

What do step down transformers do?

A

Reduce the potential difference from the transmission cables to a much lower value for domestic use

50
Q

What are fuses?

A

Fuses are safety devices. If there is a fault in an appliance which causes the live and neutral (or earth wires) to cross than a large current will flow through the fuse and cause it to melt. This will break the circuit and protect the appliance from further harm.

51
Q

What do the fuses have in terms of current?

A

Different currency based on how much current can flow through it.

A hairdryer with a current of 2A will have a 3A fuse.

Different fuses: 3A, 5A, 10A of 13A.

52
Q

How else can you protect devices?

A

Double insulate them for safety with plastic as plastic does not conduct electricity.

Physics Paper 1 (4 decks)

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