P2-Electricity

Question 1

What is potential difference

Answer 1

Is the driving force that pushes the charge around

Question 2

what is resistance

Answer 2

Is something that slows the flow down

Question 3

What does the current flowing through a component to depend on

Answer 3

Depends on the potential difference across it and the resistance of the component

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

Question 4

What are ammeters

Answer 4

Measures the current flowing through the test wire

The Ammeter must always be placed in series with whatever you’re investigating

Question 5

What is a voltmeter

Answer 5

measures the potential difference across the test wire

The voltmeter must always be placed in parallel around whatever you’re investigating

Question 6

Why is the IV characteristic of an ohmic conductor like that

Answer 6

For some components as the current through them is charged the resistance of the component changes as well

The resistance of ohmic conductor doesn’t change with the current. At a constant temperature of the current flowing through this is directly proportional to the potential difference across it

Question 7

Why is the IV characteristic of a filament lamp like that

Answer 7

When an electrical charge flows through a filament lamp it’s transfers enough energy to the thermal energy store of the filament lamp which is designed to heat up. Resistance increases with temperature so as the current increases the filament lamp heats up more and the resistance increases

Question 8

Why is the IV characteristic of a Diode like that

Answer 8

For diode the resistance depends on the direction of the current. They will happily let current flow in One Direction but have a very high resistance if it is reversed

Question 9

What does the IV graph for an ohmic conductor look like

Answer 9

It goes diagonally across the whole graph through the second and third quarters

Question 10

What does the IV graph for an filament lamp look like

Answer 10

This is a Bendy line through the second and third quarters

Question 11

What does the IV graph for an diode look like

Answer 11

This is a line increasing is deeply in the second quarter

Question 12

What is an LDR

Answer 12

This is the shorthand for light dependent resistor

An LDR is an resistor that is dependent on the intensity of light

The brightest light the resistance falls

The darkest resistance is highest

They have loads of applications including automatic night lights, outdoor lighting and burglar detectors

Question 13

What is an Thermistor

Answer 13

This is a temperature dependent resistor

In hot conditions the resistance drops

In cool conditions the resistance goes up

Thermistors make use for temperature detectors

Question 14

Water sensing circuits

Answer 14

Sensing circuits can be used to turn on or increase the power to components depending on the conditions that they are in

Question 15

What are series circuits

Answer 15

In a series circuits, the different components are are connected in a line, end to end

If you remove or disconnect one component, the circuit is broken and they all stop. This is generally not very handy and in practice very few things are connected in series

Question 16

What is the potential difference like in a series circuits

Answer 16

In series circuits the total potential difference of the supply is shared between the various components. So the potential difference around a series circuit which adds up to equal to source potential difference

Question 17

What’s the current like in a series circuit

Answer 17

In series circuit the current flows through all components

The size of the current is determined by the total potential difference of the cells and the total resistance of the circuit

Question 18

What’s the resistance like in a series circuit

Answer 18

In series circuits the total resistance of two components it’s just that some of the resistances

This is because by adding a resistor in series the two resistors have to share the total potential difference

The bigger components resistance the bigger share of the total potential difference

Question 19

What is a parallel circuit

Answer 19

In Parallel circuits each component is separately connected to the supply

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

This is obviously how most things must be connected. For example in cars and in household electrics. You have to be able to switch everything on and off

Every day circuits often include a mixture of series and parallel parts

Question 20

What is the potential difference like in a parallel circuit

Answer 20

In parallel circuit components get the full source potential difference, so the potential difference is the same across all components

This means that I don’t have boobs connected in parallel will all have the same brightness

Question 21

What is the current like in a parallel circuit

Answer 21

In parallel circuits the total current flowing around the circuit is equal to the total of all the Currents through the separate components

In a parallel circuit there are junctions with the current either splits all rejoins. The total current going into a junction has to equal the total current leaving

If two identical components are connected in parallel then the same current will flow through each component

Question 22

Why does adding a resistor in parallel reduced the total resistance

Answer 22

In parallel by three sisters have the same potential difference across them as the source

This means the pushing force making the current flow is the same as the source potential difference for each resistor that you add

But by adding another loop the current had more than one direction to go in

This increases the total current that can throw around the circuit. An increase in current means a decrease in the total resistance of the circuit

Question 23

what are the 2 type of electricity supply

Answer 23

alternating current (ac)

direct current (dc)

Question 24

what are alternating current supplies

Answer 24

the current is constantly changing direction. they are produced by alternating voltages in which the positive and negative ends keep alternating

Question 25

what are direct current supplies

Answer 25

is a current that is always flowing in the same direction. it is created by a direct voltage

Question 26

what voltage is the UK mains supply

Answer 26

is an ac supply at around 230V

Question 27

what is the frequency of an ac mains supply

Answer 27

50 cycles per second or 50Hz

Question 28

what is an example of dc supply

Answer 28

cells and batteries

Question 29

what is the meaning of 3 core cables

Answer 29

this means that that they have 3 wires inside them each with a core of copper and coloured plastic coating the colour of the coating shows it purpose the colours are always the same for all appliances

Question 30

what is the brown wire

Answer 30

Live wire The brown wire produces the alternating potential difference at about 230V from the mains supply

Question 31

what is the blue wire

Answer 31

Neutral wire the neutral wire completes the circuit and carries away the current electricity normally flows in through the live wire and out through the neutral it is around 0V

Question 32

what is the green and yellow wire

Answer 32

It is for protecting the wiring and for safety it stops the appliance casing from becoming live it doesn't usually carry a current but only when there is a fault it also at 0V

Question 33

how does the live wire give you an electric

Answer 33

your body live the earth is at 0V. this means that if you touch the live wire , a large potential difference is produced across your body and a current flows through you This causes a large electric shock which could injure or even kill you even if something is off there is a chance of getting an electric shock because there is a potential difference in the live wire any connection between live and earth can be dangerous. if they link it creates a low resistance path to earth a huge current will flow, which could result in a fire

Question 34

why is potential difference the energy transferred per charge passed

Answer 34

when an electric al charge goes through a change in potential difference, then energy is transferred Energy is supplied to the charge at the power source to 'rise' it through a potential the charge gives up this energy when it falls through any potential drop in components elsewhere in the circuit that means that a buttery with a bigger pd will supply more energy to the circuit for every coulomb of charge which flows round it because the charge is raised up 'higher' at the start

Question 35

how is electricity distributed in the uk

Answer 35

this is done by using the national grid the notional grid is a giant system of cables and transformers that cover the uk and connects power stations to consumers the national grid transfers electrical power from power station anywhere on the grid to anywhere else on the grid where it is needed

Question 36

when and how does electricity production meet demand

Answer 36

throughout the day, electricity usage changes. power stations have to produce enough electricity for everyone to have when they need they can predict when the most electricity will be used though. demand increases when people get up in the morning, come home form school or work and when it starts to get dark or cold power stations often run at well below their maximum power output

Question 37

What sort of potential difference and current do the National Grid use

Answer 37

To transmit the huge amount of power needed you need a high potential difference or a high current The problem with a high current is that you lose loads of energy as the wires heat up and energy is transferred to the thermal energy store of the surroundings It's much cheaper to boost the potential difference up really high (400,000 V) and keep the current as low as possible For a greater power, increasing the potential difference decreases the current and, which decreases the energy lost by heating the wires and the surroundings. This makes the National Grid an affective way of transferring energy

Question 38

How is the potential difference changed in the National Grid

Answer 38

To get the potential difference to 400,000 V to transmit power requires transformers as well as big pylons with a huge installation-but it's still cheaper The transformers have to step the potential difference up at one end for efficient transmission and then take it back down to safe, usable levels at the other end The potential difference is increased (steped up) using a step up transformer It's then reduced again (stepped down) for domestic use using a stepdown transformer