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[GCSE] physics > P2: Electricity > Flashcards

P2: Electricity Flashcards

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1
Q

state the equation linking charge, current and time. Give the units.

A

Q=IT
charge: coulombs
current: amperes
time: seconds

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2
Q

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

A

current is the same at all points in a closed loop

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3
Q

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

A
  1. Potential difference (V)
  2. Resistance (R)
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4
Q

what equation should be used to calculate potential difference if current and resistance are known. state the units.

A

V=IR
PD: V
current: A
resistance ( OHMS )

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5
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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6
Q

list four components for which resistance is not constant as current changes

A
  1. lamps
  2. diodes
  3. thermistors
  4. light dependant resistors ( LDRs)
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7
Q

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

A
  • resistance increases
  • ions in metals have more energy, so vibrate more
  • more frequent collisions with electrons as they flow through the metal
  • so great resistance to current flow
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8
Q

what is different about current flow through a diode?

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

state what happens to the resistance of a thermistor as temperature increases

A
  • the thermistor’s resistance decreases
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10
Q

Give two examples of when a thermistor may be used

A
  1. In a thermostat to turn a heater on below a certain temperature
  2. in a freezer to turn on a cooler when the temperature becomes too high
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11
Q

state what happens to the resistance of a LDR as light intensity decreases.

A
  • the LDR’s resistance increases
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12
Q

Give an application for a LDR

A
  • street lights often use LDRs
  • 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 a component can be connecting in a circuit?

A
  1. series ( same loop)
  2. Parallel ( adjacent loop)
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14
Q

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

A
  • series: Total P.D is shared between each component
  • parallel: P.D across each component is the same
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15
Q

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

A
  • their total resistance is less than the smallest of the two individual resistances
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16
Q

if two resistors are connected in series , what can be said about their total resistance?

A
  • their total combined resistance is equal to the sum of the two individual resistances
  • eg R1 = 5 , R2=10 total resistance = 15
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17
Q

Describe the current in a series circuit.

A
  • the current is the same at all positions
  • since the charge 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
  • when the charge reaches a junction it splits.
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19
Q

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

A
  • Ammeters should be connected in series
  • with the component that they are measuring current through
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20
Q

How should you connect a voltmeter in a circuit to measure potential difference?

A
  • Voltmeters should be connected in parallel to the component that they are measuring the potential difference of.
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21
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
  • ( i.e the circuit is still complete)
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22
Q

Define alternating and direct current.

A

a.c: current that continuously changes direction at a specific frequency
d.c: one directional current flow

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23
Q

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

A

frequency: 50Hz
Voltage: 230V

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24
Q

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

A
  1. Live wire
  2. Neutral wire
  3. Earth wire
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25
Q

what is A.C supply and a D.C supply? Is mains electricity A.C or D.C

A
  • mains electricity is an A.C supply
    a.c : alternating current
    d.c: direct current
26
Q

State the insulation colour used on:
- The Live wire
- The Earth wire
- the neutral wire

A

live wire: brown
earth wire: green and yellow stripes
neutral wire: blue

27
Q

Explain when the Earth wire carries a current

A
  • under normal circumstances, no current flows through the Earth wire
  • if a fault occurs in the appliance ( such as the surge or the casing becoming live), current will flow to the ground
28
Q

what is the potential difference is the neutral wire?

A

0 volts

29
Q

State the potential difference between the live and earth wires

A

230 volts

30
Q

what is the purpose of the neutral wire

A
  • to complete the circuit by connecting the appliance back to the mains supply
31
Q

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

A
  • Earth wire is connected to the metal casing of the appliance
  • if live wire becomes loose and touches the casing
  • the current will flow though the Earth wire , preventing electrocution
32
Q

state two equations for the power of a circuit. give appropriate units

A

P=IV
P= (current )₂ R
Power ( Watts)
Current ( Amperes)
Potential difference (Volts)
Resistance (Ohms)

33
Q

State an equation linking energy transferred, power and time

A

E=Pt
energy = Joules
Power = Watts
Time = Seconds

34
Q

State an equation linking energy transferred, potential difference and charge

A

E=QV
potential difference: volts

35
Q

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

A
  1. How long the appliance is being used for
  2. The power of the appliance
36
Q

Describe the energy transfers in a battery powered torch

A
  • battery converts chemical energy into electrical energy
  • bulb converts electrical energy into light as well as waste energy in the form of heating
37
Q

Describe the energy transfers in a battery powered motor.

A
  • battery converts chemical energy into electrical energy
  • motor converts electrical energy into kinetic energy as well as waste energy in the form of heating due to friction
38
Q

What three things determine the power of a circuit device?

A
  1. the potential difference across the circuit
  2. the current through the circuit
  3. the amount of energy transferred in a given time
39
Q

what is the purpose of the National Grid?

A
  • to link power stations to consumers so that they have access to a source of electricity
40
Q

what are the two types of transformers used in the National Grid?

A
  1. Step-Up Transformers
  2. Step-down Transformers
41
Q

what are step-up transformers found in the National Grid? What do they do?

A
  • Step-Up transformers are used when connecting power stations to transmission cables
  • They increase the potential difference
42
Q

what are step-down transformers found in the National Grid? What do they do?

A
  • Step-Down Transformers are used in connecting transmission cables to domestic buildings ( like houses)
  • they decrease the potential difference
43
Q

Why do transmission lines transfer electricity at high potential difference?

A
  • a high potential difference, results in low current
  • the lower the current, the less energy that is wasted as heat
  • therefore it is more efficient
44
Q

What does the potential difference need to be decreased between transmission lines ad houses?

A
  • safer for domestic use
  • reduces the likelihood of severe electrocution
45
Q

How does an atom become charged

A
  • If it loses an electron, it becomes a positively charged ion.

If it gains an electron, it becomes negatively charged ion.

Charged atoms are called ions.

46
Q

Give 2 properties of an insulator

A
  • electrons cannot flow
  • they are in fixed positions
47
Q

A student rubbed their jumper with a balloon, The balloon became negatively charged and the jumper became positively charged. Explain why the jumper becomes positively charged ( 3)

A
  • negatively charged electrons
  • move from the jumper to the balloon by friction
  • thus there are more positive charges ( protons) than there are negative charges ( electrons)
48
Q

A person walks along the carpet in socks and becomes negatively charged. They hold their hand near a metal door handle. Explain why a spark jumps between the person and the door handle ( 3 )

A
  • a spark jumps due to the large potential difference between the person and the door handle
  • This causes negative electrons to move through the air
  • from the person to the earthed conducting door handle
49
Q

define the term ‘ electric field ‘

A
  • the region around a charged particle which exerts a force on another charged particle
50
Q

Describe the electric field around a positively charged sphere

A
  • field lines move away to the negative charge
  • electric fields get weaker the further it is from the charged particle
51
Q

Describe the electric field around a negatively sphere

A
  • field lines move towards the negative charges
  • electric fields are weaker the further it is from the charged particle
52
Q

Describe the field between two parallel metal plates ( of different charges)

A
  • there are uniform field lines where the field strength is the same everywhere
  • the field lines are evenly spaced out
53
Q

what happens when two charged objects are brought together:
- same sign
- opposite sign

A
  • they experience a non contact electrostatic force
  • same signs: they will repel
  • opposite signs: they would attract
54
Q

1a) Two positive charges are brought together. Explain what will happen. (2)
1b) The charges are brought even closer. Describe how the strength of the force changes.(2)

A

a. - they will repel
- as their electric fields interact with each other
b. - the strength of the force increases
- as the distance between the objects decreases ( electric fields get closer)

55
Q

Explain why the negative balloon sticks to the positive jumper after it is brought close to it (2)

A
  • it sticks to the positively charged jumper as they are opposite charges
  • thus, they would attract due to the electrostatic force
56
Q

Explain why there is a spark between two charged objects ( 3 marks)

A
  • the high potential difference causes a strong electric field between the two objects
  • the strong electric field causes electrons in the air particles to be removed (ionization)
  • when the air is ionized/charged, it can conduct and so a current flow through it; this is a spark
57
Q

what is electric current?

A
  • the flow of electric charge
58
Q

What can happen when insulating materials are rubbed together?

A
  • they can become ( statically) electrically charged
59
Q

Why can insulators become electrically charged when rubbed together ?

A
  • electrons are rubbed together from one material onto the other
  • the material gaining electrons becomes negatively charged
  • the material losing electrons becomes positively charged
60
Q

Give an example of a non-contact force

A
  • the repulsive or attractive force acting between two electrically charged objects
61
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

[GCSE] physics (9 decks)

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