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Physics paper 1 > Electricity -Topic 2 > Flashcards

Electricity -Topic 2 Flashcards

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1
Q

what is an electric current

A

the flow of electric charge

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2
Q

state the equation linking charge current and time

A

Q = It —- charge = current x time

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3
Q

what two factors does the current in the circuit depend on?

A
  • potential difference
  • resistance
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4
Q

Equation for potential difference using current and resistance

A

V= IR —- P.D = current x resistance

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5
Q

what is an ohmic conductor?

A
  • a conductor for which current and potential difference is directly proportional.
  • resistance remains constant as the current changes.
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6
Q

4 components where resistance is not constant as current changes

A
  • lamps
  • diodes
  • thermistors
  • light dependant resistors
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7
Q

what happens to the resistance of a filament lamp as the temperature increases

A
  • resistance increases
  • ions in the metal have more energy, so vibrate more, causing more collisions with electrons as the flow through the metal creating greater resistance to current flow.
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8
Q

How does current flow through a diode?

A
  • the current flows in only one direction
  • resistance is very high in the other direction preventing current flow.
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9
Q

what happens to the resistance of a themistor as temp increases

A

the thermistors resistance decreases

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10
Q

give two 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 becomes too high.
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11
Q

What happens to the resistance of an LDR when the light intensity decreases?

A

The LDRs resistance increases.

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12
Q

Examples of when LDRs are used?

A
  • Street lights sometimes use them
  • When light levels become too low the light gains sufficient current to turn on.
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13
Q

what are the two ways that components can be connected in a circuit?

A
  • series (same loop)
  • parallel (adjacent loop)
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14
Q

how does the potential difference two components vary when connected in series and parallel?

A
  • in series the total P.D is shard between each component.
  • in parallel P.D across each component is the same.
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15
Q

If two resistors are connected in parallel what is their total combined resistance?

A

The total resistance is less than the smallest of the two individual resistors.

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16
Q

If two resistors are connected in series what is their total resistance?

A
  • Their total combined resistance is equal to the sum of the two individual resistances.
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17
Q

Describe the current in a series circuit

A

the current is the same in all positions as the current only has one path to flow through

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18
Q

describe the current in a parallel circuit

A

the current is shared between the different branches and then is combined again before going back to its power supply

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19
Q

how should you connect the ammeter in a circuit to measure the current

A

in series with the component they are measuring the current through.

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20
Q

how should voltmeters be connected in a circuit to measure the potential difference?

A

connected in parallel to the component they are measuring the potential difference of.

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21
Q

what is an advantage of connecting a lamp in parallel

A

if the lamp blow the rest will be unaffected and still receive current. (if the circuit is still complete)

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22
Q

what type of current is the mains electricity?

A

the mains is an a.c supply (alternating current)

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23
Q

define alternating and direct current

A
  • alternating current: current that continuously changes direction at a specific frequency.
  • direct current: one directional current flow
24
Q

what is the frequency and potential difference of the UK mains supply?

A
  • frequency:50 Hz
  • P.D: 230V
25
Q

what wires are in the cables connecting electrical appliances to the mains?

A
  • live wire
  • earth wire
  • neutral wire
26
Q

colours used for earth wire

A

green and yellow stripes

27
Q

colour of live wire

A

brown

28
Q

colour of neutral wire

A

blue

29
Q

explain why the earth wire doesn’t carry a current

A
  • normally no current flows through the earth wire.
  • is a fault occurs in the appliance current will flow to the ground.
  • As the earth wire has virtually no resistance a large current flows, this causes the fuse to blow preventing further current.
30
Q

P.D at neutral wire

A

0V

31
Q

P.D between live and earth wires

A

230 V

32
Q

what is the purpose of the neutral wire

A

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

33
Q

In metal appliances where is the earth wire connected to? Why?

A
  • the earth wire is connected to the metal casing of the appliance.
  • If the live wire becomes loose and touches the metal casing the current will flow through the earth wire preventing electrocution.
34
Q

two equations for the power of a circuit

A
  • P = IxV
  • P = (I)2 x R
35
Q

equation linking energy transfer power and time

A

E = P x t

36
Q

equation linking energy charge and P.D

A

E = Q x V

37
Q

two main factors that energy transfer in an appliance depends on

A
  • how long the appliance is being used for
  • the power of the appliance
38
Q

describe the energy transfers in a battery powered torch

A
  • battery converts chemical energy into electrical energy.
  • bulb converts electrical energy into light energy and waste energy in the form of heat.
39
Q

energy transfers in battery powered motor

A
  • battery converts chemical energy in to electrical energy.
  • motor converts electrical energy into kinetic energy and waste energy in the form of heat due to friction.
40
Q

three things that determine the power of a circuit device.

A
  • potential difference across the circuit
  • current through the circuit
  • The amount of energy transferred in a given time
41
Q

what is the explain why the earth wire doesn’t carry a current purpose of the national grid

A

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

42
Q

what are the two types of transformers used in the national grid

A
  • step - up transformer
  • step - down transformer
43
Q

where are the step up transformers found on the national grid? What do they do?

A
  • used when connecting power station to transmission cables
  • increase the P.D and decrease the current
44
Q

where are step down transformers found in the national gird? what do they do?

A
  • used when connecting transmission cables to domestic buildings (e.g houses)
  • decrease P.D increase current
45
Q

why do transmission lines transfer electricity at high P.D

A
  • High P.D results in a low current
  • The lower the current the less energy wasted as heat
  • Therefore it is more efficient
46
Q

why does 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 serious electrocution.
  • Appliances are designed for 230 V
47
Q

what can happen when insulating materials are rubbed together?

A

they become electrically charged

48
Q

why can insulators become electrically charged when rubbed together?

A
  • electrons are rubbed form one material onto another.
  • the material gaining electrons becomes negatively charged.
  • the material losing electrons becomes equally positively charged.
49
Q

what happens when two electrically charged objects are brought 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 brought close together

A

they exert an attractive force on each other and attract

52
Q

give an example of a 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 in which a charged object will experience a non contact electrical force

54
Q

where can electrical fields be found

A

surrounding any charged object

55
Q
A

Physics paper 1 (2 decks)

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