TOPIC 2/3 Flashcards
(102 cards)
1
Q
What is electric current
A
It is a flow of electrical charge.
2
Q
How will electrical charge flow round in a circuit
A
The electrical current will only flow through a complete closed circuit if there is a potential difference
3
Q
What is the unit of the ampere
A
A
4
Q
What is potential differences
A
It is the driving force that pushes the charge round (V)
5
Q
That is resistance
A
It is anything that slows the flow down (ohm)
6
Q
What does the current following depend on
A
It depends on the potential difference across it and the resistance of the component
7
Q
What is the size of the current
A
The rate of flow of charge
8
Q
What is the given formula for when a current flows past a point in a circuit for length of time then the charge
A
Q =it
9
Q
The formula linking of and current is very useful
A
Potential difference (v) current (a) x resistance
10
Q
What does the resistance of a current depend on
A
A number factors, like whether components are in series or parallel or the length on the wire used in the circuit
11
Q
What does the ammeter do
A
It measures the current flowing through the test wire
The ammeter must always be place in a series
12
Q
What does the voltmeter do
A
Measures the potential difference across the test wire in volts
The voltmeter must always be placed in parallel
13
Q
For some components, as the current changes what other component changes as well
A
Resistance
14
Q
What does the resistance of some resistors and components do
A
Change a diode or a filament
15
Q
What happens when an electrical current flows through a filament lamp
A
It transfers some energy to the thermal energy store of the filament which is designed to heat up
16
Q
What does resistance increases
A
It increases the temperature,so as the current increases, the filament lamp heats up more and the resistance increase
17
Q
How does the diodes effect the direction the resistance goes in
A
They will happily let current glow in one direct but have a very high resistance if it is reversed
18
Q
What does the term I-V characteristic show
A
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
Q
What does a linear components have
A
They have an I-V characteristic that’s a straight line
20
Q
What do non-linear components have
A
A cured I-V characteristic
21
Q
What is an LDR
A
A resistor
22
Q
What does an LDR resistance depend on
A
The intensity of light
23
Q
What is a resistance like in a bright light
A
The resistance falls
24
Q
What happens to the resistance when it’s dark
A
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
