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Physics > Electricity > Flashcards

Electricity Flashcards

1
Q

What is electrical current?

A

Flow of electrical charge

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2
Q

What is the size of electric current?

A

The rate of flow of electrical charge

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3
Q

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

A

Charge flow = current x time

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4
Q

How is current distributed in a single closed loop?

A

Same value at any point

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5
Q

What two things is the current through a component dependent on?

A

The resistance and potential difference across the component

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6
Q

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

A

potential difference = current x resistance

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7
Q

What is the relationship between current through an ohmic conductor and potential difference across a resistor?

A

Directly proportional

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8
Q

Is the resistance of components such as lamps, diodes, thermistors and LDRs constant?

A

No, it changes with the current through the component

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9
Q

Does the resistance of a filament lamp increase or decrease with the temperature of the lamp?

A

The resistance of the filament lamp increases as the temperature does

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10
Q

T/F: A diode has a very high resistance in one direction

A

True, the current through a diode flows in one direction only, the diode has very high resistance in the reverse direction

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11
Q

Does the resistance of a thermistor increase or decrease as the temperature increases?

A

The resistance of a thermistor decreases as the temperature increases

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12
Q

Does the resistance of an LDR increase or decrease as light intensity increases?

A

The resistance of an LDR decreases as light intensity increases

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13
Q

How can LDRs be used in circuits?

A

Turning on lights when it gets dark

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14
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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15
Q

List 4 components for which resistance is not constant as current changes

A

Lamps, diodes, thermistors, LDRs

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16
Q

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

A

Resistance increases because 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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17
Q

What is different about current flow through a diode?

A
  • Current only flows in one direction
  • Resistance is very high in the other direction, preventing current flow
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18
Q

Give 2 examples of when a thermistor may be used

A
  • in a thermostat to turn a heater on below a certain temperature
  • in a freezer to turn on a cooler when the temperature gets too high
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19
Q

What are 2 ways a component can be connected in a circuit?

A
  • series
  • parallel
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20
Q

How does the p.d across 2 components vary when connected in series and parallel?

A

series - total p.d is shared
parallel - p.d is the same across each component

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21
Q

If 2 resistors are connected in parallel, what can be said about their combined total resistance?

A

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

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22
Q

If 2 resistors are connected in series, what can be said about their total resistance?

A

total combined resistance is equal to the sum of the 2 individual resistances

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22
Q

Describe the current in a series circuit

A

current is same in all positions (current only has one path to flow thru)

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23
Q

Describe the current in a parallel circuit

A

current is shared between the different branches, when the charge reaches a junction it splits

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24
Q

How should you connect an ammeter in a circuit to measure current?

A

in series with the component they’re measuring current through

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25
Q

How should you connect a voltmeter in a circuit to measure p.d?

A

in parallel to the component they’re measuring p.d of

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26
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 (circuit is still complete)

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27
Q

What is resistance measured in?

A

Ohms

28
Q

What is charge measured in?

A

Coulombs

29
Q

Is mains electricity an a.c supply or a d.c supply?

A

a.c supply

30
Q

What does a.c stand for?

A

alternating current

31
Q

What does d.c stand for?

A

direct current

32
Q

Define a.c

A

current that continuously changes direction at a specific frequency

33
Q

Define d.c

A

one directional current flow

34
Q

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

A

50 Hz
230V

35
Q

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

A
  1. Live
  2. Neutral
  3. Earth
36
Q

What is the insulator colour used on the Earth wire?

A

Yellow and green stripes

37
Q

What is the insulator colour used on the live wire?

A

brown

38
Q

What is the insulator colour used on the neutral wire?

A

blue

39
Q

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

A
  • normally no current flows through the Earth wire
  • if a fault occurs in the appliance (surge/casing becoming live), current will flow to the ground
40
Q

What potential is the neutral wire at?

A

0 volts

41
Q

State the p.d between the live & earth wires

A

230V

42
Q

What is the purpose of the neutral wire?

A

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

43
Q

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

A
  • metal casing of the appliance
  • if live wire becomes loose and touches metal casing, current will flow through earth wire, preventing electrocution
44
Q

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

A

P = I V
(watts, amps, volts)

P = I^2 R
(watts, amps, ohms)

45
Q

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

A

E = P t
(joules, watts, seconds)

46
Q

State an equation linking energy transferred, charge flow and p.d. Give appropriate units.

A

E = Q V
(joules, coulombs, volts)

47
Q

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

A
  1. how long the appliance has been used for
  2. the power of the appliance
48
Q

Describe the energy transfers in a battery powered torch

A
  • battery converts chemical to electrical
  • bulb converts electrical to light (waste - thermal)
49
Q

Describe energy transfers in a battery powered motor

A
  • battery converts chemical to electrical
  • motor converts electrical to kinetic (waste - thermal from friction)
50
Q

What 3 things determine the power of a circuit device?

A
  1. p.d across the circuit
  2. current thru circuit
  3. amount of energy transferred in a given time
51
Q

What is the purpose of the National Grid?

A

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

52
Q

What are the 2 types of transformers used in the National Grid?

A

step-up & step-down

53
Q

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

A
  • used when connecting power stations to transmission cables
  • increase p.d
54
Q

Where are step-down transformers found in he National grid? What do they do?

A
  • used when connecting transmission cables to domestic buildings
  • decrease p.d
55
Q

Why do transmission lines transfer electricity at high potentials?

A

high p.d results in low current, low current means less energy is wasted as heat, making it more efficient

56
Q

Why does the p.d need to be decreased between transmission lines and houses?

A

lower p.d is safer for domestic use and reduces the likelihood of severe electrocution, appliances are designed for 230V

57
Q

What can happen when insulating materials are rubbed together?

A

they become statically electrically charged

58
Q

Why can insulators become electrically charged when rubbed together?

A

electrons are rubbed from one material onto the other, material gaining electron becomes negatively charged, the one losing becomes equally positively charged

59
Q

What happens when 2 electrically charged objects are brought close together?

A

exert a force on each other

60
Q

What happens when 2 identically charged objects are brought close together?

A

exert a repulsive force on each other and repel

61
Q

What happens when 2 oppositely charged objects are brought close together?

A

exert an attractive force on each other and attract

62
Q

Give an example of a non-contact force

A

repulsive or attractive force acting between 2 electrically charged objects

63
Q

What is an electric field?

A

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

64
Q

Where can electrical fields be found?

A

surrounding any charged object

65
Q

Describe the electrical field around a charged particle

A

strongest closest to the object, decreases in strength as you move away from the object

66
Q

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

A

force between them becomes stronger

67
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

Physics (8 decks)

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