TOPIC 2/3 Flashcards Preview

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Flashcards in TOPIC 2/3 Deck (102):
1

What is electric current

It is a flow of electrical charge.

2

How will electrical charge flow round in a circuit

The electrical current will only flow through a complete closed circuit if there is a potential difference

3

What is the unit of the ampere

A

4

What is potential differences

It is the driving force that pushes the charge round (V)

5

That is resistance

It is anything that slows the flow down (ohm)

6

What does the current following depend on

It depends on the potential difference across it and the resistance of the component

7

What is the size of the current

The rate of flow of charge

8

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

Q =it

9

The formula linking of and current is very useful

Potential difference (v) current (a) x resistance

10

What does the resistance of a current depend on

A number factors, like whether components are in series or parallel or the length on the wire used in the circuit

11

What does the ammeter do

It measures the current flowing through the test wire
The ammeter must always be place in a series

12

What does the voltmeter do

Measures the potential difference across the test wire in volts
The voltmeter must always be placed in parallel

13

For some components, as the current changes what other component changes as well

Resistance

14

What does the resistance of some resistors and components do

Change a diode or a filament

15

What happens when an electrical current flows through a filament lamp

It transfers some energy to the thermal energy store of the filament which is designed to heat up

16

What does resistance increases

It increases the temperature,so as the current increases, the filament lamp heats up more and the resistance increase

17

How does the diodes effect the direction the resistance goes in

They will happily let current glow in one direct but have a very high resistance if it is reversed

18

What does the term I-V characteristic show

It refers to a graph which shows how the current(I) flowing through a component changes as the potential difference across it is increased

19

What does a linear components have

They have an I-V characteristic that’s a straight line

20

What do non-linear components have

A cured I-V characteristic

21

What is an LDR

A resistor

22

What does an LDR resistance depend on

The intensity of light

23

What is a resistance like in a bright light

The resistance falls

24

What happens to the resistance when it’s dark

The resistance is at its highest

25

What do LDR applications include

Automatic night lights, outdoor lighting and burglar detectors

26

What is a thermometer

It is a temperature dependent resistor

27

What happens to the resistance when the conditions are hot and cool

The resistance drops when it’s hot and it does up when it cools

28

What are thermistors useful for

Temperature detectors
Eg car engine temperature sensors and electric thermostats

29

What can sensing circuits be used for

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

30

In a series circuit how are the components connected

They are connected in a line, end to end

31

What happens when you disconnect int component in a series circuit

The circuit is broken and they all stop. This is generally not very handy and in practice very few things are connected in serious

32

In a series circuit how much amount of current flows through all components

The same amount of current flows through all components

33

What determines the total current

By the total potential difference of the cells and the total resistance of the circuit

34

In a series circuit what is total resistance of two components

It is the the sum of their resistance this is because by adding a resistor in a series circuit the two resistors have to share the total potential difference

35

Why is the total current reduced when a resistor is added

In a series circuit, the current is the same everywhere. This means the total resistance of the circuit increases

36

When cell PD is added what happens to the series circuit

There is a much bigger pd when more cells are in series, if they’re all connected the same way

37

How are the components in a parallel circuit connected

They are separately connected to the supply

38

Will the circuit be effected if one of the components is removed in a parallel circuit

If you remove or disconnect one of them it will hardly affect the others at all

39

How is parallel circuits useful in homes

Because you need to be able to switch things off separately

40

How much current flows through the circuit in a parallel circuit

The total current flowing around the circuit is equal to the total of all the currents through the separate components

41

Is a resistor is added in a parallel circuit what is effected

It reduces the total resistance. If you have two resistance in parallel their total resistance is less than the resistance is the smallest of the two resistance

42

What are the two type of electrical force

Alternating current and direct current

43

In a alternating current what is constantly changing

The direction

44

What are alternating currents produced by

They are alternating voltages in which the positive and negative ends keep alternating

45

What is the UKs main supply in a home

Around 230 v

46

What is direct current

Is a current that is always flowing in the same direction. It’s created by a direct voltage

47

What does the colour of a cable show

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

48

What is the colour brown show about a wire

LIVE WIRE- brown
The live wire provides the alternating potential difference(at about 230V) from the mains supply

49

What does the colour blue show about the wire

Neutral wire
The neutral blue colour completes the circuit and carried away current

50

What does the earth wire show about the wire (green and yellow )

It is for protecting the wiring, and for safety- it stops the appliance casing from becoming live.

51

Which is the three separate wires can give you an electric shook

Live wire. Your body is OV this means that If you touch the live wire, a large potential difference if produced across your body and a current flows through you

52

How can an electric shook effect you

It could injure or even kill you

53

Will you still be electrocuted If the plug socket or a light switch is turned off

There is still a danger of an electric shook. Even though there ain’t current flowing but pd is still live

54

If a switch is turned and no current is flowing so can you still get electricuted

Is you mate contact me with the live wire, your body would provide a link between the supply and the earth, so a current would flow to you

55

Give an example of an electrical appliance that is designed to transfer energy to components in the circuit when a current flows

For example kettle transfer energy electrically from the mains alternating current supply to the thermal energy store of the heating element inside the kettle

56

What does energy transfer depend on

Depends on power

57

What does the total energy transfer by an appliance depend on

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

58

What is the total power of an appliance

It is the energy that it transfers per second. So the more energy it transfers in a given time time, the higher it’s power

59

What is the amount of energy transferred by electrical work formula

Energy transfer (J) = Power (w) x Time (s)
(E=pt)

60

What are appliances often given on

A power rating- labelled with a maximum safe power that they cab operate at.

61

What does the rating tell you about the appliance used

It tells you the maximum amount of energy transferred between stored per second when the appliance is in use

62

How can the power rating help a customer choose between the models

The lower the power rating, the less electricity an appliance uses in a given time and so the cheaper it is to run

63

What is the formula more power

E = QV

64

What does power depend on also

Current and potential difference

65

Give the formula for the power of an appliance to be found

Power(w)= potential difference (v) x current (A) (P=VI)

66

What is the formula given if you don’t know the potential difference

P= IR

67

What is the national grid

The National grid is a giant web of wires that covers the whole of brain, getting electricity from the power stations to homes everywhere

68

Where is electricity distributed from

The National grid

69

How does the National grid transfer energy

It’s transfers energy from the power stations anywhere on the grid to anywhere else in the grid where it’s needed (homes), and (industry)

70

If electricity changes throughout the day how does that effect the amount of electricity a power station has to produce

Power stations have to produce enough electricity for everyone to have it when they need it

71

How can a power station predict when the most electricity is used during a day or an event

It increases when people get up in the morning, come home from school or work and when it gets dark or cold outside. Popular events like a sporting final shown on TV could also cause a peak in demand

72

If a power station breaks down what happens

There’s a spare capacity to cope with a high demand, even if there’s an unexpected shut down of another station

73

What do you need to transfer a huge amount of power

You need either a highly potential difference or a high current

74

What is the problem of having a high current

The problem is that you lose load of energy as the wires heat up and energy is transferred to the thermal energy store of the surroundings

75

How is potential difference increases when using a step-up transfer

The potential difference is increased using a step-up transformer and it’s then reduced again (stepped down) for domestic use using a a step-down transformer

76

What are the three matters

Solid
Liquid
Gas

77

What is the same and what is different in a matter particles

The particles substance in each state are the same- only the arrangement and energy of the particles are different

78

Explain the particles of a solid

Strong forces of attraction hold the particles together in a fixed position. The particles don’t have much energy so they can only vibrate about their fixed position

79

Describe the particles of liquid

There are weaker forces of attraction between the particles. The particles are closer together, but can move past each other. They have more energy than the particles in a solid
They move in random direction at low speeds

80

What are the particles of a gas

There are almost no forces of attraction between the particles. The particles have more energy than in liquids and solids- they are free to move and are constantly moving with a random directions and speeds

81

What can colliding gas particle produce

Pressure

82

What happens when particles are free to move

As they move they bang into each other and whatever else happens to get in the way

83

What is pressure

It is the force exerted per unit area

84

How do particles act in sealed containers

The outward gas pressure is the total force by all of the particles in the gas on a unit area of the container walls

85

What happens when you increase the temperature of gas

The average speed of its particles increases. This is because the energy in the particles kinetic energy stores

86

So if a gas has a constant volume...

Increasing its temperature increases its pressure

87

If the particles are in a container what happens to the speed they are traveling in

It means that they hit the sides as the container more often in a given amount of time

88

Which other factor increases the total force exerted on a unit area

Momentum, which means that they exert a larger force when they collide with the container

89

What is density

It is a measure of trust ‘compactness’ of a substance.

90

What are the units of density

Kg/m

91

Formula of density

Density = mass/ time

92

What does the density of a particles depend on

What it’s made of and how it’s particles are arranged

93

What is a dense particle

It is a particle packed tightly together

94

What does it mean if the particles have less dense

That density varies between different states of matter
Solids are generally denser than liquid and gases are usually less dense than liquids

95

What do the particles in a system do

Vibrate or move around- they have energy in their kinetic energy stores, they also have potential energy stores due to their position

96

What is the internal energy of a system

The total energy that its particles have in their kinetic and potential energy stores

97

What happens when you heat a system

It transfers to energy to its particles increasing the internal energy

98

What leads to a change in temperature or change in state

Heating a system

99

When died s state change occur

If the substance is heated enough- the particles will have enough energy in their kinetic energy stores to break the bonds holding them together

100

What is a solid state

Physical change- this means you don’t end up with a new substance- it’s the same substance as you started with just a different form

101

What happens when you reverse a change in state

The substance will return to its original form and get back its original properties

102

What does it mean if a number of particles don’t change

This means mass is conserved-none of it is lost when the substance changes state