Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Physics Year 10 > Topic 2 - Electricity > Flashcards

Topic 2 - Electricity Flashcards

You may prefer our related Brainscape-certified flashcards:
Physics 101 flashcards AP® Physics flashcards
1
Q

What is electric current

A

A flow of electrical charge

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

When will current flow

A

-In a closed circuit when there is a potential difference as charge only flows if there is a potential difference

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is potential difference

A

The driving force that pushes the charge round

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is resistance

A

Anything that slows the flow in a circuit

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

How does the current depend on potential difference and the resistance of a component

A

-The greater the resistance across a component the smaller the current that flows

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the equation for charge when current flows past a point in a circuit for a length of time

A

Q = I x T
Charge (coulombs) = current (amperes) x time (seconds

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the formula linking potential difference, current and resistance

A

Potential = Current x Resistance
V (volts) = I (ampere) x R (ohms)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Outline the factors effecting resistance practical

A
  1. Attach crocodile clip to the wire level with 0cm on the ruler
  2. Attach a second crocodile clip to the wire (e.g. 10cm away from first clip)
  3. Close the switch, then record the current through the wire and the pd across it
  4. Open the switch then move the second crocodile clip another 10cm along the wire. Close the switch again, then record the new length, current and pd
  5. Repeat this for a number of different lengths of the test wire
  6. Use your measurements of current and pd to calculate the resistance for each for each length of wire
  7. Plot a graph of resistance against wire length and draw a line of best fit
    8.Your graph should be a straight line through the origin, meaning resistance is directly proportional to length - the longer the wire, the greater the resistance
  8. If the graph doesn’t go through the origin your first clip may not be attached at 0cm (systematic error)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

In the factors effecting resistance practical where should the ammeter be and for what purpose

A

-Must always be placed in series with whatever you’re investigating
-Measures the current flowing through the test wire

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

In the factors effecting resistance practical where must the voltmeter be and for what purpose

A

-Must always be placed in parallel around whatever you’re investigating - NOT around any other bit of the circuit
-Measures the potential difference across the test wire

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the current flowing through an ohmic conductor directly proportional to

A

The potential difference across

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Why do filament lamps increase resistance

A

-When an electrical charge flows through, it transfers some energy to the thermal energy store of the filament which is designed to heat up
-Resistance increases with temperature so as the current increases, the filament lamp heats up more and the resistance increased

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How do diodes affect resistance

A

The resistance depends on the direction of the current. They will let current flow in one direction, but have a very high resistance if it is reversed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Outline I-V characteristics practical

A

-Set up circuit composed of : battery, (chosen component), ammeter, voltmeter and a variable resistor
-Begin to vary the resistor which alters the current flowing through the circuit and pd across the component
-Take several pairs of readings from the ammeter and voltmeter to see how the potential difference across the component varies as the current changes. Repeat each reading twice more to get an average pd at each current
-Swap over the wires connected to the battery, so the direction of the current is reversed
-Plot a graph of current against voltage for the component

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What should the I-V characteristic graph show for ohmic conductor

A

The current through an ohmic conductor (at constant temperature) is directly proportional to potential difference so you get a straight line

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What should the I-V characteristic graph show for a filament

A

-As the current increases, the temperature of the filament increases, so the resistance increases as the higher temperature increases the vibrations of the ions in the filament, which makes it harder for the electrons to get past.
-This means less current can flow per unit pd, so the graph gets shallower

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is a LDR

A

-An LDR is a resistor that is dependent on the intensity of light
-In bright light, the resistance
-In darkness, the resistance is highest
-They have a lot applications such as automatic night lights, outdoor lighting and burglar detectors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is a thermistor

A

-A thermistor is a temperature depending resistor
-In hot conditions, the resistance drops
-In cool conditions, the resistance goes up
-Thermistors make useful temperature detectors (e.g. car engine temperature sensors and electronic thermostats)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What can sensing circuits be used for

A

To turn on or increase the power to components depending on the conditions that they are in

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

How would a sensing circuit control a fan in a room

A

-The fixed resistor and fan will always have the same potential difference across
-The pd of the power supply is shared out between the thermistor and and the loop made up of the fixed resistor and the fan according to their resistances - the bigger a components resistance the more of the pd it takes
-As the room gets hotter the resistance of the thermistor decreases and it takes a small share of the old from the power supply, so the of across the fixed resistor and fan rises, making the fan go faster

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

How could you connect a component in a sensing circuit across a variable resistor

A

-If you connect a bulb in parallel to an LDR, the pd across both the LDR and bulb will be high when it’s dark and the LDR’s resistance is high
-The greater the pd across a component, the more energy it gets
-So a bulb connected across an LDR would get brighter as the room got darker

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What are series circuits

A

-The different components are connected in a line, end to end, between the +ve and -ve of the power supply
-If you disconnect one component, the circuit is broken and they all stop. This is generally not handy and in practice very few things are connected in series

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What are the exception to series circuits

A

-Voltmeters which are always connected in parallel
-However they don’t count as part of the circuit

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

How can you find potential differences round a series circuit

A

-The total pd of the supply in a series circuit is shared between the various components
-Therefore the pds round a series circuit always add up to equal the source pd
V(total) = V(1) + V(2) etc

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

How is current shared across a series circuit

A

-The same current flows through all components
- I(1) = I(2)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

In series circuits how do you find the total resistance of two components

A

It’s the sum of their resistances

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

How do resistors work in a series circuit

A

-By adding a resistor in series, the two resistors have to share the total pd
-The pd across each resistor is lower, so the current through each resistor is also lower. In a series the current is the same everywhere do the total current is reduced when a resistor is added which means the total resistance of the circuit increases
-The bigger a components resistance, the bigger it’s share of the total pd

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

How does potential difference work in series circuit

A

-There is a bigger pd when more cells are in series, if they’re all connected the same way
-For example when two cells with a potential difference of 1.5V are connected in series they supply 3V between them
-The differences add up

29
Q

How do parallel circuits work

A

-Each component is separately connected to the +ve and -ve of the supply
-If you remove or disconnect one of them it will hardly affect the other at all

30
Q

What is the exception for parallel circuits

A

-Ammeters which must be connected in a series circuit

31
Q

Where are parallel circuits used

A

-They’re much more sensible than series circuits
-In cars and household electrics as you can switch everything on and off separately
-Everyday circuits often include a mixture of series and parallel psrts

32
Q

How does potential difference work in parallel circuits

A

-In parallel circuits all components get the full source pd, so the potential difference is the same across all components
-This means that identical bulbs connected in parallel will all be at the same brightness
-V(1) = V(2)

33
Q

How does current in parallel circuits

A

-In parallel circuits the total current flowing around the circuit is equal to the total of all the currents through the separate
-In a parallel circuit there are junctions where the current either splits or rejoins. The total current going into a junction has to equal the total current leaving
-If two identical components are connected in parallel then the same current will flow through each component
-I(total) = I(1) + I(2) + etc.

34
Q

How do resistors work in parallel circuits

A

1.If you have two resistors in parallel, their total resistance is less than the resistance of the two resistors
2. -In parallel both resistors have the same potential difference across them as the source
-This means the ‘pushing force’ making the current flow is the same as the source pd for each resistor that you add
-But by adding another loop the current has more than one direction to go in
-This increases the total current that can flow around the circuit. Using V = IR, an increasing in current means a decrease in the total resistance of the circuit

35
Q

How do you investigate resistors in a series circuit

A

-Build a circuit with a battery, resistor and ammeter and note the pd of the battery
-Measure the current through the circuit using the ammeter. Use this to calculate the resistance of the circuit using R = V / I
-Add another resistor, in series with the first
-Again, measure the current through the circuit and use this and the pd of the battery to calculate the overall resistance of the circuit
-Repeat till 4 resistors have been added
-Plot a graph of the number of resistors against the total resistance of the circuit

36
Q

How do you investigate resistors in a parallel circuit

A

-Using the same equipment as before, build the same initial circuit
-Measure the total current through the circuit and calculate the resistance of the circuit using R = V / I
-Next add another resistor, in parallel with the first
-Measure the total current through the circuit and use this and the potential difference of the battery to calculate the overall resistance of the circuit
-Repeat and until added all of the resistors
-Plot a graph of the number of resistors in the circuit against the total resistance

37
Q

What results should you find from investigating resistors in a series circuit

A

-Adding resistors in a series increases the total resistance of the circuit decreases the total current through the circuit
-The more resistors you add, the larger the resistance of the whole circuit

38
Q

What results should you find from investigating resistors in a parallel circuit

A

-As you add resistors the total current through the circuit increases so the total resistance of the circuit has decreased
-The more resistors added the smaller the overall resistance becomes

39
Q

What is ac (alternating current)

A

The current is constantly changing direction and is produced by alternating voltages in which the positive and negative ends keep alternating

40
Q

What is the U.K. mains supply

A

An ac supply at around 230V

41
Q

What is the frequency of the ac mains supply

A

50 cycles per second (hertz)

42
Q

What type of current do batteries and cells supply

A

direct current

43
Q

What is direct current

A

Is a current that is always flowing in the same direction created by a direct voltahe

44
Q

What are the three wire made of in electrical appliances

A

Three core cables with wires inside them, each with a core of copper and a coloured plastic coating

45
Q

Why do the three core cables in most electrical appliances have colours

A

It shows the purpose, the colours are always the same for every appliance. This is so that it is easy to tell the different wires apart.

46
Q

What does the blue wire do in electrical appliances

A

Neutral - Completes the circuit - when the appliance is operating normally, current flows through the live and neutral wires. It is around 0V.

47
Q

What does the brown wire do in electrical appliances

A

Live wire - Provides the alternating pd (230V) from the main power supply

48
Q

What does the green and yellow wire do in electrical appliances

A

Earth wire - Protecting the wiring, and for safety. It stops the appliance casing from becoming live. It doesn’t usually carry a current - only when there’s a fault, It’s also at 0V.

49
Q

How can the live wire give you an electric shock

A

Your body is at 0V so if you touch the live wire, a large pd is produced across your body and a current flows through you. This causes a large electric shock that could kill you.

50
Q

How can you get an electric shock even if a switch or plug socket is turned off

A

There is still a danger of electric shock. A current isn’t flowing but there’s still a pd in the live wire. If you made contact with the live wire, your body would provide a link between the supply and earth, so a current would flow through you.

51
Q

Why is any connection between live and earth wires dangerous

A

If the link creates a low resistance path to earth, a huge current will flow which could result in a fire

52
Q

How does a kettle transfer energy to components in a circuit

A

Transfer energy electrically from the main ac supply to the thermal energy store of the heating element inside the kettle

53
Q

How do handheld fans transfer energy to components in the circuit

A

Energy is transferred electrically from the battery of handheld fan to the kinetic energy store of the fan’s motor

54
Q

What happens when appliance transfers aren’t all useful

A

The higher the current, the more energy is transferred to the thermal energy store of the components (and then the surroundings)

55
Q

What does the total energy transferred by appliance depend on

A

How long the appliance is on for and it’s power

56
Q

What is the power of an appliance

A

The energy that it transfers per second. So the more energy transferred in a given, the higher it’s power.

57
Q

What is the equation of energy transferred by electrical work

A

Energy transferred = Power x time
E (J) = P (W) x T (S)

58
Q

What are power ratings

A

Appliances are given them and they are labelled with the maximum safe power that they can operate at. The power rating tells you the maximum amount of energy transferred stores per second when the appliance is in use.

59
Q

How does power rating on appliances help customers

A

Helps them choose between models - the lower the power rating, the less electricity an appliance uses in a given time and so the cheaper it is to run

60
Q

Why does a higher power not necessarily mean that it transfers more energy usefully

A

An appliance may be more powerful than another, but less efficient, meaning that it might still only transfer the same amount of energy to useful stores

61
Q

What happens when an electrical charge goes through a change in pd

A

Energy is transferred and supplied to the change at the power source to raise it through a potential. The charge gives up this energy when it falls through any potential drop in components elsewhere in the circuit. This means that a battery with a pd will supply more energy to the circuit for every coulomb of charge which flows round it, because the charge is raised up ‘higher’ at the start

62
Q

What’s the equation that links energy transferred, charge flow and potential difference

A

Energy transferred = charge flow x potential difference
E (J) = Q (C) x V (V)

63
Q

What is the equation that links power, pd and current

A

Power = potential difference x current
P (W) = V (V) x I (A)

64
Q

How do you find power if you don’t know the potential difference

A

P = I^2 x R
Power = current ^2 x resistance

65
Q

What the national grid

A

A giant system of cables and transformers that covers the U.K. and connects power stations to consumers (anyone who is using electricity)

66
Q

What does the national grid do

A

Transfers electrical power from power stations anywhere on the grid to anywhere else on the grid where it’s needed (e.g. homes and industry)

67
Q

Why does electricity production have to meet demand

A

Throughout the day, electricity usage changes. Power stations have to produce enough electricity for everyone to have it when they need it.

68
Q

When is electricity demand highest

A

-Demand increases when people get up in the morning, come home from school or work and when it starts to get dark or cold outside.
-Popular events like a sporting final being shown could also cause a peak in demand

69
Q

Why do power stations often run below their maximum output

A

-So there’s spare capacity to cope with a high demand, even if there’s an unexpected shut-down of another station
-Lots of smaller power stations that can start up quickly are also kept in standby just in case

Physics Year 10 (5 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions