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Physics paper 1 > Electricity > Flashcards

Electricity Flashcards

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1
Q

What is electric current?

A

A flow of electrical charge

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2
Q

What is potential difference?

A

The driving force that pushes the charge around

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3
Q

What is the unit of current?

A

Amperes

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4
Q

What is resistance?

A

Anything that slows the flow down. it is measured in ohms

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5
Q

What is the relationship between resistance and current?

A

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

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6
Q

What is the size of the current?

A

The rate for flow charge

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7
Q

How do you work out charge flow?

A

Charge flow = current x time

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8
Q

How do you work out potential difference?

A

Potential difference = current x resistance

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9
Q

What properties do ohmic conductors have?

A

Their resistance does not change with the current and at a constant temperature, the current flowing through an ohmic conductor is directly proportional to the potential difference across it

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10
Q

What will an ohmic conductor look like on an I-V characteristic graph?

A

A straight line going diagonally across it

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11
Q

What will a filament lamp look like on an I-V characteristic graph?

A

An f shape going across it

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12
Q

What will a diode look like on an I-V characteristic graph?

A

A straight line that then curves up

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13
Q

What are the properties of an LDR?

A

In bright light resistance falls and in darkness, resistance is at its’ highest

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14
Q

What are the properties of a thermistor?

A

In hot conditions the resistance goes up and in cool conditions, the resistance goes down

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15
Q

What is a sensing circuit?

A

A circuit which can be used to turn on or increase the power to components depending on the conditions that they are in

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16
Q

How is a series circuit set out?

A

The different components are connected in a line, end to end, between the +ve and -ve of the power supply

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17
Q

What are current, potential difference and resistance like in a series circuit?

A

Potential difference is shared, current is the same everywhere and resistance adds up

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18
Q

What is the equation for potential difference in a series circuit?

A

Vtotal = V1 + V2 + …

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19
Q

What is the equation for current in a series circuit?

A

I1 = 12 = …

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20
Q

What is the equation for resistance in a series circuit?

A

Rtotal = R1 + R2 + …

21
Q

Are the other components affected if one is removed in a parallel circuit?

A

They are hardly affected at all

22
Q

Are series or parallel circuits more common and why?

A

Parallel because in a series circuit, if one of the components in removed or breaks then the whole circuit stops working but this doesn’t happen in parallel circuits

23
Q

How do current and potential difference behave in parallel circuits?

A

Potential difference is the same across all components and current is shared between branches

24
Q

What happens when you add a resistor in a parallel circuit?

A

The total resistance is reduced

25
Q

Why is the total resistance is reduced when you add a resistor to a parallel circuit?

A

By adding another loop, the current has more than one direction to go in which increases the total current, and an increase in current results in a decrease in total resistance (V=IR)

26
Q

What are the properties of alternating current?

A

The current is constantly changing direction and it is produced by alternating voltages

27
Q

What is the frequency of ac mains supply?

A

50 cycles per second or 50 Hz

28
Q

What are the properties of direct current?

A

It is always flowing in the same direction and is created by a direct voltage from cells and batteries

29
Q

What colour is the neutral wire and what does it do?

A

Blue; it completes the circuit and carries away the current

30
Q

What colour is the live wire and what does it do?

A

Brown; it provides the alternating potential difference

31
Q

What colour is the earth wire and what does it do?

A

Green and yellow; it protects the wiring and stops the appliance casing from becoming live. It also carries current if there is a fault

32
Q

What happens if you touch a live wire?

A

A large potential difference is produced across your body and the current flows through you, which gives you an electric shock and can result in death

33
Q

What transfers energy?

A

A moving charge

34
Q

How do you work out energy transferred?

A

Energy transferred = power x time

35
Q

What does the power rating on an appliance tell you?

A

The maximum operating power; the maximum amount of energy transferred between stores per second when the appliance is in use

36
Q

How do you work out energy transferred if you don’t know the power?

A

Energy transferred = charge flow x potential difference

37
Q

How do you work out power?

A

Power = potential difference x current

38
Q

How do you work out power if you don’t know the potential difference?

A

Power = current² x resistance

39
Q

What is the national grid?

A

A giant system of cables and transformers that covers the UK and connects power stations to consumers

40
Q

Why do power stations run well below their maximum power output?

A

So there’s spare capacity to cope with high demand or if another power station unexpectedly shuts down

41
Q

Why does the national grid use a high pd and a low current?

A

Because high current loses lots of energy through heat so it’s much cheaper to boost the pd really high

42
Q

What do the transformers do in the national grid?

A

They step the pd up at one end for efficient transmission and then bring it down to safe and usable levels at the other end

43
Q

What causes a build up of static?

A

Friction

44
Q

How is a static charge made?

A

When insulating materials are rubbed together, negative electrons are transferred from one to the other, leaving one with a positive charge and one with a negative (from the extra electrons)

45
Q

How are sparks caused?

A

Electric charge builds up which causes the potential difference to increase which means that electrons can jump across the gap between the charged object and the earth, causing a spark.

46
Q

How is an electric field created?

A

When an object is electrically charged, an electric field forms around it

47
Q

How can you show the field around an electrically charged object?

A

By using field lines

48
Q

Which direction do electric field lines go in?

A

From positive to negative

49
Q

What do the distance between electric field lines show?

A

The strength or weakness of the electric field

Physics paper 1 (4 decks)

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