Electricity

Question 1

What is electric current?

Answer 1

A flow of electrical charge

Question 2

What is potential difference?

Answer 2

The driving force that pushes the charge around

Question 3

What is the unit of current?

Answer 3

Amperes

Question 4

What is resistance?

Answer 4

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

Question 5

What is the relationship between resistance and current?

Answer 5

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

Question 6

What is the size of the current?

Answer 6

The rate for flow charge

Question 7

How do you work out charge flow?

Answer 7

Charge flow = current x time

Question 8

How do you work out potential difference?

Answer 8

Potential difference = current x resistance

Question 9

What properties do ohmic conductors have?

Answer 9

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

Question 10

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

Answer 10

A straight line going diagonally across it

Question 11

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

Answer 11

An f shape going across it

Question 12

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

Answer 12

A straight line that then curves up

Question 13

What are the properties of an LDR?

Answer 13

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

Question 14

What are the properties of a thermistor?

Answer 14

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

Question 15

What is a sensing circuit?

Answer 15

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

Question 16

How is a series circuit set out?

Answer 16

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

Question 17

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

Answer 17

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

Question 18

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

Answer 18

Vtotal = V1 + V2 + …

Question 19

What is the equation for current in a series circuit?

Answer 19

I1 = 12 = …

Question 20

What is the equation for resistance in a series circuit?

Answer 20

Rtotal = R1 + R2 + …

Question 21

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

Answer 21

They are hardly affected at all

Question 22

Are series or parallel circuits more common and why?

Answer 22

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

Question 23

How do current and potential difference behave in parallel circuits?

Answer 23

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

Question 24

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

Answer 24

The total resistance is reduced

Question 25

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

Answer 25

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)

Question 26

What are the properties of alternating current?

Answer 26

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

Question 27

What is the frequency of ac mains supply?

Answer 27

50 cycles per second or 50 Hz

Question 28

What are the properties of direct current?

Answer 28

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

Question 29

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

Answer 29

Blue; it completes the circuit and carries away the current

Question 30

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

Answer 30

Brown; it provides the alternating potential difference

Question 31

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

Answer 31

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

Question 32

What happens if you touch a live wire?

Answer 32

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

Question 33

What transfers energy?

Answer 33

A moving charge

Question 34

How do you work out energy transferred?

Answer 34

Energy transferred = power x time

Question 35

What does the power rating on an appliance tell you?

Answer 35

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

Question 36

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

Answer 36

Energy transferred = charge flow x potential difference

Question 37

How do you work out power?

Answer 37

Power = potential difference x current

Question 38

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

Answer 38

Power = current² x resistance

Question 39

What is the national grid?

Answer 39

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

Question 40

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

Answer 40

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

Question 41

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

Answer 41

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

Question 42

What do the transformers do in the national grid?

Answer 42

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

Question 43

What causes a build up of static?

Answer 43

Friction

Question 44

How is a static charge made?

Answer 44

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)

Question 45

How are sparks caused?

Answer 45

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.

Question 46

How is an electric field created?

Answer 46

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

Question 47

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

Answer 47

By using field lines

Question 48

Which direction do electric field lines go in?

Answer 48

From positive to negative

Question 49

What do the distance between electric field lines show?

Answer 49

The strength or weakness of the electric field