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Physics > Section 9 - Electricity And Circuits > Flashcards

Section 9 - Electricity And Circuits Flashcards

(110 cards)

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1
Q

What do all metals have in their electronic configuration?

A

One or two weakly attracted electrons on the outer shell

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2
Q

Why does metal wire have many free electrons?

A

Because the outer electron on the metal is easily removed

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3
Q

What does the voltage do when a wire is attached to the battery?

A

It pushes the free electrons around the circuit

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4
Q

How come electrons always move towards the the positive terminal of the battery?

A

Because electrons are negative so are attracted to the positive terminal of the battery

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5
Q

What is conventional current direction?

A

When direction goes from the positive terminal to the negative terminal of the battery

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6
Q

What are circuit diagrams used to show?

A

The components and junctions in a circuit

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7
Q

What are the two types of circuits?

A

Series and parallel

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8
Q

Which way does electricity move around a series circuit?

A

Just around one route, one way

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9
Q

What is different about parallel circuits to series?

A

Parallel circuits have junctions so more than one route for the current to go down

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10
Q

Can you switch lamps on and off individual in a series or parallel circuit?

A

Series- no as they’ll all switch off / parallel- yes in each junction a lmao can be switched off separately

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11
Q

What is current measured in?

A

Amperes (amps) / using an ammeter

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12
Q

How is the ammeter used in a circuit?

A

It’s connected in series to make sure the current’s passing through a component or a circuit

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13
Q

Does the total current change when going through the circuit?

A

No- the current leaving the positive terminal is the same as the current arriving at the negative terminal

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14
Q

Why is the current the same at the beginning and then end?

A

Because current is conserved

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15
Q

What does conserved mean?

A

A quantity that is kept the same throughout

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16
Q

What happens to current in a parallel circuit to make sure it all gets electricity but has the same current when arriving at the negative terminal?

A

The current splits at the junctions to travel along different branches / the total amount entering the junction is the same amount that’s leaving

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17
Q

Why do you need a potential difference in a circuit?

A

To push current around the circuit

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18
Q

What is potential difference?

A

The difference in the energy carried by electrons before and after they’ve flowed through a component

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19
Q

What is potential difference also known as?

A

Voltage

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20
Q

What is a model for potential difference?

A

Marbles on a ramp

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21
Q

What would happen to the marbles on a flat surface?

A

They won’t move

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22
Q

What happens when there is a height difference in the ramp that the marbles are on?

A

They can roll down the ramp

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23
Q

So what is the ramp in the model signifying?

A

The ramp is the potential difference (without the ramp the marbles won’t move)

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24
Q

What happens if the circuit is open?

A

The current won’t flow

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25
What contains the source of potential difference?
The cell or battery
26
How do electrons move when a current flows?
They move together
27
What is the current like if there is a bigger potential difference?
The current is bigger
28
Which terminal of the cell/battery does the current flow out from?
Negative
29
What is it that flows around the circuit?
Electrons
30
What do the electrons carry from the cell?
Energy
31
Where does the energy go?
To the components
32
Which way do we draw current moving?
Battery cell)————
33
Why do we draw the arrow to show direction of current going towards the negative when we know it moves towards the positive?
Many years ago we thought that current moved from positive to negative (convectional current) but now we know it doesn’t (electrical current)
34
Which way does electrical current / coventional current go?
Electric goes from the negative to the positive / conventional goes from the positive to the negative (these are the arrows not the actual flow of current, electrical current is the only actual direction but we draw a conventional)
35
Does the potential difference in a parallel circuit ever change?
No
36
What is potential difference measured in?
Volts using a voltmeter
37
Where is the voltmeter in a circuit?
Parallel to components
38
Why do some wires and components need a larger potential difference to produce a current?
Because there may be a large electrical resistance
39
What is resistance?
A way of saying how difficult it is for electricity to flow through something
40
What is resistance measured in?
Ohms
41
What is the equation to calculate resistance?
Potential difference / current = resistance (potential difference = current x resistance)
42
What happens to the total resistance of the circuit when resistors are connected in series?
The total resistance is increased because the pathway become sharper for current to flow through
43
Is potential difference shared through resistors?
Yes
44
Is potential difference split equally across resistors?
No - a greater potential difference for resistors with higher resistances
45
What is the total resistance of a circuit when resistors are connected in parallel?
The circuit is less than the resistance of the individual resistors, because there are now mor empathy’s for the current
46
What does a variable resistor do?
Change the current in the circuit
47
What would you add to a circuit to check whether a resistor has the correct value or to measure an unknown resistor?
A variable resistor
48
What happens when potential difference changes across a fixed resistor?
The current changes by the same percentage
49
Because the current changes as the potential difference changes, what does this mean they’re in?
Direct proportion
50
Why does current and potential difference form a straight line going through the origin?
Because resistance stays the same
51
Name 2 other components that have resistances that change when potential difference changes
Filament lamps and diodes
52
What happens to a filament lamp as it’s current increases it’s heat?
It’s resistance increases
53
So what happens when potential difference increases in a filament lamp?
The more the current flows which makes the lamp hotter and whiter and the heat increases the resistance (as the particles are moving more so it’s harder for the energy to pass through, so it needs more potential difference) / the current doesn’t change by the same percentage
54
If potential difference is going in one direction what happens to the resistance in a diode?
It is low, but when it goes in the other direction it is very high
55
Which way can current flow through a diode?
Only one way, otherwise the resistance is very high
56
What happens to resistance in a LDR when it is dark?
It has a high resistance
57
What happens to the resistance in a LDR when light intensity increases?
The resistance gets smaller
58
How come a light is on when there is too much resistance?
Because if there is too little resistance then too much current goes to the component as switches the light off
59
What happens to current when you increase the potential difference?
The current increases
60
At a low temperature, does a thermistor have a high or low resistance?
High resistance
61
As the temperature increases, what happens to the resistance in a thermistor?
The resistance decreases
62
Why do circuits warm up when there is a current?
Because all circuits have some resistance
63
Why is energy transferred when current passes through s resistor?
Because electrical work is done against the resistance
64
How do we know energy has been transferred through a resistor?
Because the resistor becomes warm as energy is transferred by heating
65
What is the heating effect (energy transferring by heat against a resistor) useful for?
Using a kettle or electric heater
66
Why is the heating bad in computers and plugs?
Because it’s useful energy that is being wasted, by dissipating and the surroundings gain thermal energy
67
What is inside a resistor?
Free electrons that move through a lattice of positive ions
68
What happens inside a resistor when electrons flow through them?
They collide with the ions, the more collisions they make the harder for them to pass through so the electrical resistance is higher
69
What happens when electrons collide with ions?
They transfer energy to them
70
How do you reduce resistance in circuits?
By using wires made from metals with low resistance
71
Name a wire and types of wires that have low resistance
Copper / thick wires / cooled metals so the lattice doesn’t vibrate so much
72
Why is having less resistance in s circuit better?
Because then less energy is transferred by heating and less is dissipated
73
How does electrical energy transform to other types of energy?
When the electrons collides with ions in the metal, it transforms the energy into other forms
74
What does resistance tell us?
The potential difference to drive a current through a component
75
What are you doing by adding a resistor to a current?
Sharing the pd so there is less current through the lamp
76
What does the arrow in the diode show?
Direction of conventional current
77
What are diodes useful for?
Controlling the flow of current
78
How do you find the total resistance of two resistors in a series circuit?
You add the the ohms of the resistors together
79
What happens to the total resistance of 2 resistors in a parallel circuit?
The total resistance is less than the resistance of the smallest resistor
80
Why will total distance be less in a parallel circuit?
Because there is 2 pathways for current to take so more total current will flow through the circuit
81
What will happen to resistance in a parallel circuit if current increases but pd does not?
Total resistance will decrease
82
What do thermistors do?
Decrease resistance when temperature increases
83
When a thermistor is at a low temperature does it have a high or low resistance?
High resistance
84
What does a variable resistor practical help us to see?
The distance of wire is directly proportional to resistance
85
What is a zero error?
A reading on a measurement where it should be 0 but isn’t due to a fault in the equipment
86
What could the faults in the equipment when doing a core practical be.
Crocodile clips doesn’t exactly touch 0 / wire is too hot (increasing resistance
87
How would you decrease the problem of the wire being too hot?
Only allow current to flow when taking a measurement and turn it off once you are done
88
What is the equation to calculate energy transferred?
Current x potential difference x time
89
What does permanent magnet mean?
Always magnetic
90
What can a magnet do?
Attract magnetic materials
91
Name 3 metallic metals
Iron, steel, nickel and cobalt
92
What is the space around a metal that can attract other metal called?
A magnetic field
93
When do bar magnets repel each other?
When two norths or two south sides a pushed together
94
What is an induced magnet?
When a magnetic material in a magnetic field becomes a magnet itself
95
Name 3 electrical devices where magnets are used
Electric motors, generators, loud speakers and other electrical devices
96
Name 2 simple things that use magnets
Door latches and knife holders
97
What do you use to find the shape of a magnetic field?
Plotting compasses
98
How do we represent magnetic fields?
Using lines that show how a single North Pole would move (from north to south)
99
Where is the field in the magnetic field strongest?
Where the lines are closer together
100
What is a uniform magnetic field?
Where two flat magnets have the same strength and direction everywhere
101
How come compasses can always help people find their way?
As the needle always points to a position near the earth’s North Pole
102
Why are compasses needles weighted at one end?
To keep them level as otherwise it will tilt relative to the horizontal by different amounts in different places
103
What proves that the earth has a magnetic field?
The behaviour of compasses, shows the earth has a similar magnetic field to a bar compass
104
What is thought to cause the earth’s magnetic field?
Electric currents in the molten outer core
105
What is the earth’s molten outer core made up from?
A mixture of nickel and iron, two magnetic materials
106
What does a current flowing through a wire cause?
A magnetic field
107
What do you use to see the shape of a magnetic field around a wire carrying a current?
Iron filings
108
What does the direction of the magnetic field depend on?
The direction of the current
109
What happens if a current changes direction?
The direction of the magnetic field
110
What happens if you point your thumb in the direction of the current (+ to -)
The magnetic field goes in the direction your fingers are pointing

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