Electricity in the home

Question 1

Electric current is the movement of ….. …… To transfer energy it … …. … …. the charge …. are going. That’s why …… current works.

Answer 1

charge carriers
doesn’t matter which ways, carriers
alternating

Question 2

What voltage is the UK mains supply?
What type of current supply is it?
What type of supply are batteries?

Answer 2

230V
AC
DC

Question 3

What is an AC supply?

What is its frequency?

Answer 3

An alternating current which means it’s constantly changing direction
50Hz

Question 4

What does DC mean?

Answer 4

Direct current, it only travels in one direction

Question 5

What is an oscilloscope? (CRO cathode ray oscilloscope)?

Answer 5

A voltmeter

Question 6

What happens if you plug an AC supply into an oscilloscope, what do you see?

Answer 6

You would get a trace on the screen, showing how the voltage changes with time
The trace goes up and down in a regular pattern between +ve and -ve.

Question 7

What happens if you plug in a DC into an oscilloscope?

Answer 7

You get a straight line

Question 8

What does the vertical height of the AC supply at any point of the trace show on an oscilloscope?
By measuring the height of the trace you can find what?

Answer 8

The input voltage at that point.

The potential difference of the AC supply

Question 9

How do you find the voltage on a DC current on an oscilloscope?

Answer 9

Look at where the trace crosses the voltage axis on the screen

Question 10

On the oscilloscope what is the GAIN dial?

What is the Timebase dial?

Answer 10

The dial that controls how many volts each centimeter division represents on the vertical axis (voltage)
It controls how many milliseconds each division represents on the x axis - time

Question 11

What does a DC source look like on an oscilloscope?

Answer 11

As it is always at the same voltage it goes in a straight line

Question 12

What does an AC source look like on an oscilloscope?

Answer 12

It gives a regularly repeating wave, from which you can work out the time period and frequency of the supply

Question 13

How do you work out frequency?

Answer 13

Frequency Hz = 1/ Time period (s)

Question 14

List the hazards associated with electricity in the home? (9)

Answer 14

Long cables, frayed cables, cables in contact with something hot or wet
Water near sockets, shoving things into sockets
Damaged plugs, too many plugs into one socket (extension lead)
Lighting sockets int he ceiling without bulbs in them
Appliances without their covers on

Question 15

How are most electrical items connected to the mains? Which mean they have what inside them? These have a core of … and a coating of …… ……..

Answer 15

With three core cables
Three cables inside them
Copper, plastic coating

Question 16

What is the brown live wire?

Answer 16

The wire with the volts that carries the alternating current, between a high +ve and -ve volatge

Question 17

The blue wire is the ….. always at ….v

Electricity normally flows out through only the …. and … wires.

Answer 17

neutral wire, 0V

live and neutral

Question 18

What is the green and yellow wire?
What’s it for and what does it do?
What is it attached to, therefore doing what?

Answer 18

The earth wire
Protecting the wire and for safety as it works together with a fuse to prevent a fire and socks.
The metal casing of the plug and carries electricity to the earth away from you should something go wrong with the live or neutral wires and they touch the metal case.

Question 19

Describe the wiring for a three pin plug…

1. What happens with the left coloured wire (which is it)?
2. What is the middle wire and where does it sit?
3. What is the right wire and what is it connected to?
4. What are the pins made of?
5. What holds the wires down as they come into the casing?

Answer 19

1. It is the neutral blue wire and is connected to its pin by being firmly screwed in
2. In the middle and plugs into the top pin and is screwed in, the Earth wire
3. The live brown wire, the fuse
4. Brass
5. Cable grip tightly fastens the outer layer of the wires

Question 20

Different appliances need … amounts of … energy.

Thicker cables have … …….. so they carry more ….

Answer 20

different, electrical

less resistance, current

Question 21

Why are the pins in the plug made of copper or brass?

Why are the case and cable grips made out of rubber or plastic? These all mean what?

Answer 21

They are good conductors.
they are very good insulators and are flexible
Electricity is kept flowing where it should

Question 22

1. If there is a fault where the live wire touches the metal case, what happens?
2. What happens to the fuse and then what does this do?
3. What’s now happened to the appliance?

Answer 22

1. Because the case is earthed, a too greater current flows through the case and out through the earth wire.
2. The surge in current melts the fuse (or trips the circuit breaker) when the current is greater than the fuse rating . This cuts of the live supply and breaks the circuit.
3. It’s been isolated making it impossible to get an electric shock and prevents the risk of fire cause by the heating effect of a large current

Question 23

What, as well as people, are fuses and earthing there to protect?
How should fuses be rated?
Why does fuse rating need to increase with the thickness of the cable?

Answer 23

The circuits and wiring to stop them being fried if there is a surge in current.
Just higher than the normal operating current
The larger the current the thicker the wire needed to carry it.

Question 24

Appliances with metal cases are usually what, to reduce the danger of electric shock?
What does earthing mean?
Can an earthing conductor become live?

Answer 24

earthed
the case must be attached to an earth wire
no

Question 25

What is a double insulated appliance? | Anything with double insulation doesn't need what, the rest are called what?

Answer 25

An appliance has a plastic case with no metal parts showing | an earth wire, live and neutral, two-core cables

Question 26

What are circuit breakers? What do they do that is similar to fuses?

Answer 26

An electrical safety device used in some circuits. Like fuses they protect the circuit from damage if too much current flows.

Question 27

What happens when circuit breakers detect a surge in current? How can a circuit breaker be reset? Why does this make them more convenient than fuses? Yet they are ....

Answer 27

They break the circuit by opening a switch Flicking a switch on the device. They can be reset when fuses need replaced once melted, but CB are a lot more expensive than fuses

Question 28

What is one type of circuit breaker? What happens if someone touches the live wire? So what happens to the neutral wire? So what does the RCCB do?

Answer 28

RCCB - a residual current circuit breaker Deadly current will flow through them into the earth It ends up carrying less current than the live wire It detects the difference and quickly switches of the power by opening the switch.

Question 29

Why are RCCBs better than fuses? (2)

Answer 29

They work much faster and break the circuit as soon as there is a current surge, no time is wasted melting a fuse, this makes them safer. They detect smaller currents not large enough to melt a fuse but still deadly enough, making them more protective against electrocution.

Question 30

``` Cells and batteries ... energy into their ..... Light : Motion: Heat: Sound: ```

Answer 30

``` electrical, components lamps motors kettles speakers ```

Question 31

When is electrical energy converted into heat energy in a circuit? The more current flowing the more...... A bigger voltage means more ..... because it .... more ... through. Filament bulbs work by passing current through a very .... .... heating it up .... .... that it ..... . Wasting a lot of ..... in the form of ..... .

Answer 31

Whenever a current flows through anything with electrical resistance (everything) Heat prodcued Heating, pushes, current thin wire, so much, glows. energy, heat

Question 32

If an appliance is efficient it .... These appliances do what with their energy? For example: However....?

Answer 32

wastes less energy transfer most of their energy of total electrical output into useful energy Less energy is wasted as heat in power saving lamps such as compact fluorescent lamp and light emitting diode, instead of an ordinary filament lamp. They are more expensive but they overtime you save more money on your bills so you save more than the original investment.

Question 33

What do power ratings tell you? | What is the equation for energy transferred?

Answer 33

How much energy a device transfers per second | ETransferred = Power rating x time

Question 34

What is the formula for electrical power? | What do most electrical goods do so you can decide what fuse to use after working out the current?

Answer 34

Power = current x P.D | Power rating and voltage rating

Question 35

When an .... charge goes through a ... in P.D, then .... is transferred.

Answer 35

electrical, change, energy

Question 36

Energy is supplied to the charge at the .... .... to raise it through a ..... The charge gives up this .... when it falls through any .... ... in components else where in the circuit. What is the formula for energy transformed?

Answer 36

power source, P.D energy, potential drop, = charge x potential difference

Question 37

The bigger the change in ..... the more energy is ... for a given amount of charge passing through the circuit. This means that a battery with a bigger voltage will supply what? because the charge is raised up higher at the start and more energy will be dissipated in the circuit too.

Answer 37

P.D, transferred | more energy to the circuit for every coulomb of charge which flows around the circuit