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Physics > 1.2. Electricity > Flashcards

1.2. Electricity Flashcards

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1
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2
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3
Q

What are the 2 things needed for charge to flow through a circuit?

A

For charge to flow:
- The circuit must be closed
- There must be a source of potential difference (e.g. battery/cell)

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4
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What is electric current?

A

Electric current is the flow of electrical charge (flow of electrons?)

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5
Q

Define the size of an electric current?

A

The size of the electric current is the rate of flow of electrical charge

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6
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What is the equation linking charge flow, current and time

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7
Q

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

A

A current has the same value at any point in a single closed loop (in a series circuit)

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8
Q

What is potential difference?

A

Potential difference is a measure of the energy transferred for each electron that passes through a component

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9
Q

What does the potential difference of 1 volt tell us?

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The potential difference of 1 volt tells us that 1 joule of energy is transferred for each coulomb of electrons that moves through the circuit

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10
Q

What 2 factors does the size of current through a component depend on?

A

The current through a component depends on:
- The resistance of the component
- The potential difference across the component

(As V=IR)

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11
Q

The greater the resistance of a component…

A

The greater the resistance of a component, the smaller the current for a given potential difference across the component

R = V / I

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12
Q

What is the equation linking current, potential difference and resistance

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13
Q

How should you connect a voltmeter to a circuit?

A

You should connect a voltmeter to a circuit in parallel to the component you are trying to find the potential difference of

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14
Q

How should you connect an ammeter to a circuit?

A

You should connect a ammeter to a circuit in series

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15
Q

What does Ohm’s Law state?

A

The current through an ohmic conductor at a constant temperature is directly proportional to the potential difference across it

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16
Q

What is an ohmic conductor?

A

An ohmic conductor is a conductor for which the current and potential difference are directly proportional

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17
Q

What happens to the resistance in an ohmic conductor?

A

The resistance remains constant as the current changes

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18
Q

Give one example of an ohmic conductor?

A

A wire

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19
Q

Describe the resistance of a filament lamp?

A

The resistance of a filament lamp increases as the temperature of the filament increases

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20
Q

What is different about current through a diode?

A
  • The current only flows through one direction
  • The resistance is very high in the reverse direction
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21
Q

Describe the resistance of a thermistor

A

The resistance of a thermistor decreases as the temperature increases

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22
Q

Give one application of where thermistors may be used?

A

Thermistors may be used in thermostats

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23
Q

Describe the resistance of a LDR compared to light intensity

A

The resistance of an LDR decreases as light intensity increases

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24
Q

Give one application of where a LDR may be used?

A

A LDR may be used when switching lights on when it gets dark

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25
Q

List 4 examples of non-ohmic conductors?

A
  • Lamps
  • Diodes
  • Thermistors
  • LDRs
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26
Q

Describe the current in a series circuit

A

In a series circuit, the same current passes through each component

(The current is the same at all points of the circuit)

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27
Q

Describe the potential difference in a series circuit

A

In a series circuit, the total potential difference of the power supply is shared between the components

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28
Q

What is the total resistance of a series circuit?

A

The total resistance of a series circuit is equal to the sum of the resistance of each component

29
Q

Describe the potential difference for components connected in a parallel circuit

A

For components connected in a parallel circuit, the potential difference across each component is the same

30
Q

Describe the current in a parallel circuit

A

In a parallel circuit, the total current through the whole circuit is the sum of the currents through the separate components

31
Q

Describe the total resistance of two resistors in parallel

A

The total resistance of two resistors in parallel is less than the resistance of the smallest individual resistor

32
Q

What are the differences between series and parallel circuits?

A
33
Q

Explain the effects of adding resistors in series and parallel circuits

A

Adding resistors in series increases the total resistance, whilst adding resistors in parallel decreases the total resistance

34
Q

Explain why adding resistors in parallel decreases the total resistance?

A

Adding resistors in parallel decreases the total resistance as:
- Resistance = Potential Difference / Current (R = V/I)
- Each parallel resistor creates an extra path along which the current can flow
- There is more current flowing whilst the battery potential difference is the same, so there is less resistance

35
Q

What is the advantage of connecting lamps in parallel?

A

If one lamp blows, the rest will be unaffected and can still recieve current

36
Q

Define Direct Current (DC) and Alternating Current (AC)

A
  • Direct Current (DC) is current that flows in one direction only
  • Alternating Current (AC) is current that continuously changes its direction at a specific frequency
37
Q

Give one example of Direct Current (DC)

A

Cells and batteries

38
Q

What type of current supply is the UK mains electricity?

A

The UK mains electricity is an alternating current supply (AC)

39
Q

What is the frequency and potential difference of the UK mains electricity?

A

The UK mains electricity has a frequency of 50Hz and potential difference of 230V

40
Q

How are most electrical appliances are connected to the mains?

A

Most electrical appliances are connected to the mains using three-core cable

41
Q

What are the colours of the three-core cables connecting the electrical appliances to the mains?

A

Live wire – brown
Neutral wire – blue
Earth wire – green and yellow stripes

42
Q

What is the function of the live wire?

A

The live wire carries the alternating potential difference from the supply

43
Q

Why may live wires be dangerous?

A

A live wire may be dangerous, even if mains circuit is off, as current may still be flowing through it

44
Q

What is the function of the neutral wire?

A

The neutral completes the circuit formed by the live wire

45
Q

Why is the neutral wire less dangerous than the live wire?

A

It has a lower voltage than the live wire

46
Q

What is the function of the Earth wire?

A
  • The earth wire is a safety wire to stop the appliance becoming live
  • The potential difference is 0V, only carries current if there is a fault
47
Q

Explain how the Earth wire works

A
  • The metal casing of an appliance is attached to an Earth wire
  • The Earth wire is connected to the Earth
  • If the metal casing becomes live, the current will flow through the Earth wire, preventing electrocution
48
Q

What is the danger of providing any connection between the live wire and earth

A

The danger is that if someone touched the live wire, a current would flow through the person to the Earth and they’d be electrocuted

49
Q

What is the potential difference between the live wire and earth (0 V)?

A

The potential difference between the live wire and earth (0 V) is about 230 V

50
Q

What is the equation linking power, potential difference and current?

A

power = current x potential difference
P = I V

P in watts (W)
V in volts, (V)
I in amps (A)

51
Q

What is the equation linking power, current and resistance?

A

power = current2 x resistance
P = I2R

P in watts (W)
R in ohms, (Ω)
I in amps (A)

52
Q

What are everyday electrical appliances designed to do?

A

Everyday elecrical appliances are designed to transfer energy

53
Q

What does the amount of energy an everyday electrical appliance transfers depends on?

A

The amount of energy an everyday electrical appliance transfers depends on:
- How long the appliance is switched on for
- The power of the appliance

54
Q

What are the common ways energy is usually transferred in electrical appliances?

A

Energy is usually transferred in electrical appliances from batteries or ac mains

55
Q

When is electrical work done?

A

Electrical work is doen when charge flows through a circuit

56
Q

What are the 2 formulas for energy transferred?

A
57
Q

Explain the role of the National Grid?

A
  • The National Grid is a system of cables and transformers linking power stations to consumers and transfers electrical power
58
Q

What are step-up transformers used for?

A

Step-up transformers are used to increase the potential difference from the power station to the transmission cablesso that less curent is wasted

59
Q

What are step-down transformers used for?

A

Step-down transformers are used to decrease the potential difference to a much lower value for domestic use

60
Q

Why is the National Grid system an efficient way to transfer energy?

A
  • The step up transformers increase the voltage / potential difference by several thousand volts
  • This means that the same amount of power can be transferred using a much smaller current (as P = I V) so less current is wasted
61
Q

What happens when certain insulating materials are rubbed against each other?

A
  • They become electrically charged objects
  • Negatively charged electrons are rubbed off one material and on to the other
  • The material that gains electrons becomes negatively charged
  • The material that loses electrons is left with an equal positive charge
62
Q

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

A
  • When two electrically charged objects are brought close together they exert a force on each other
  • Two objects that carry the same type of charge repel
  • Two objects that carry different types of charge attract
63
Q

Give an example of a non-contact force

A

Electrostatic forces of attraction

64
Q

How do sparks occur?

A
  • Sparking occurs when enough charge builds up, and the objects are close but not touching
  • The charge jumps through the air from the highly negative object to the highly positive object, to balance out the charges
65
Q

How do we prevent sparks?

A

Objects are earthed

66
Q

How do we know if objects are charged or not?

A

Charged objects exert forces of attraction or repulsion on one another when not in contact

67
Q

What does a charged object create?

A

A charged object creates an electric field around itself

68
Q

Describe the electric field of a charged object

A
  • The electric field is strongest close to the charged object
  • The further away from the charged object, the weaker the field
69
Q

What are the electric field patterns for an isolated charged sphere?

A

Physics (10 decks)

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