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physics > P2: Electricity > Flashcards

P2: Electricity Flashcards

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1
Q

What is current?

A

the flow of electrical charge measured in amperes (A)

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2
Q

What do you use to measure current?

A

an ammeter connected in series

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3
Q

What is the current like in series?

A

the same at all points in a circuit

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4
Q

What is resistance?

A

a measure of how a component resists the flow of charge

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5
Q

What happens with an increased resistance?

A

the more difficult it is for charge to flow, the lower the current

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6
Q

What is resistance measured in?

A

ohms

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7
Q

What is potential difference?

A

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

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8
Q

What are the effects of an increased potential difference?

A

the greater the flow of charge, the greater the current

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9
Q

What is potential difference measured in? And with what?

A

volts (V) using a voltmeter in parallel

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10
Q

What are current-potential difference graphs used for?

A

to show the relationship between the potential difference and current for any component

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11
Q

On an I-V graph, what does a straight line through the origin indicate?

A

current and potential difference are directly proportional, resistance is constant

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12
Q

On an I-V graph, what does a steep gradient indicate?

A

low resistance, as a large current will flow for a small potential difference

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13
Q

On an I-V graph, what does a shallow gradient indicate?

A

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

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14
Q

What is the difference between the currents across series and parallel circuits?

A

series - current is the same throughout
parallel - the total current drawn from the power supply is the sum of the currents through the separate components

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15
Q

What is the difference between the potential difference on series and parallel circuits?

A

series - the total potential difference of the power supply is shared between the components
parallel - potential difference is the same across each component

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16
Q

What is resistance like in series?

A

the total resistance of two components is the sum of the resistance of each component because the current has to travel through each component in turn

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17
Q

What is resistance like in parallel?

A

the total resistance of two resistors is less than the resistance of the smallest individual resistor because there are more paths for the current to take - it can take one or the other, allowing it to flow more easily

18
Q

What happens when resistors are added in series?

A

increase in the total resistance

19
Q

What happens when more resistors are added in parallel?

A

reduce in the total resistance

20
Q

What is the power of a device?

A

a measure of the rate at which energy is transferred or work is done

21
Q

What does power depend on?

A

the potential difference across it and the current flowing through it

22
Q

Describe direct current

A
  • has a potential difference that is always positive or negative (current direction is constant)
  • is the type of current that is supplied by cells and batteries
23
Q

Describe alternating current

A
  • has a potential difference that alternates from positive to negative (the current direction alternates)
  • is the type of current used in mains electricity
24
Q

What is the voltage and frequency of UK mains electricity?

A

230V and 50Hz

25
Q

What is the potential difference of each of the wires in the three core cable?

A
  • live wire (brown) - 230V
  • neutral wire (blue) - at or close to the 0V earth potential
  • earth wire (green and yellow stripes) - 0V
26
Q

What happens during the operation of a three-core cable?

A
  • the potential difference causes current to flow through the live and neutral wires
  • the live wire carries the alternating potential from the supply
  • the neutral wire completes the circuit
  • current will only flow in the earth wire if there is a fault connecting it to a non-zero potential
27
Q

What is effieciency?

A

the ratio of useful energy out to total energy in

28
Q

When charge flows, it has to overcome the resistance of the circuit. This requires energy, what happens as a result of this?

A
  • work is done when charge flows
  • the amount of work done depends on the amount of charge that flows and potential difference
29
Q

What is the national grid?

A

a system of cables and transformers linking power stations to homes and businesses

30
Q

What is the function of a power station?

A

transfers the energy supply into electrical energy

31
Q

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

A

larger 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 bigger the boiler, so the higher the steam temperature

32
Q

What is the function of step up transformers?

A

increase the potential difference from the power station to the transmission cables. this reduces current and, therefore, reduces the heating effect caused by current flowing in the transmission cables

33
Q

How does reducing the heating effect in the transmission cables make them more efficient?

A

reduces energy loss

34
Q

What is the function of the transmission cables?

A

transfer electricity

35
Q

What is the function of the step down transformers?

A

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

36
Q

What is the potential difference of the transmission cables?

A

400,000V

37
Q

What can happen when insulating materials are rubbed together?

A

they can become electrically charged

38
Q

When two insulating materials are rubbed together what is the effect of the friction between the two?

A

it moves negatively charged electrons from one material to another, the object that gains electrons becomes negatively charged and the one that loses electrons becomes positively charged

39
Q

What happens to the charge because both of the materials are insulators? How would this differ with conductors

A

the charge remains on the object. they conduct charge to the earth so it cannot build up

40
Q

What is an isolated object?

A

an object that has no conducting path to earth

41
Q

What happens when the charge on an isolated object increases?

A

the potential difference between the object and the earth increases, when this becomes high enough, a spark may jump across the gap, from the object to any earthed conductor near it.

42
Q

What does the strength of the electric field at any point depend on?

A
  • the distance from the object (further away means a weaker field)
    -the amount of charge (higher charge means a stronger field)

physics (4 decks)

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