17 Practical Electricity

“PRACTICAL ELECTRICITY”

Combined Science 5129BENGKEL KECEMERLANGAN AKADEMIK 2015

ELECTRICAL POWER & ENERGYDANGERS OF ELECTRICITY

SAFE USE OF ELECTRICITY IN THE HOME

LEARNING OUTCOMES

WHAT IS ELECTRICITY ?

Electricity is a form of energy.

It is an energy created when electrons move continuously through a conductor.

USES OF ELECTRICITY

Electrical Heating

Electrical Lighting

Generating Movement

ELECTRICAL LIGHTINGElectrical Energy to Light Energy

Filament Bulb

Fluorescent Bulb

CompactFluorescent Bulb

L.E.D Bulb

Electricity is used to provide light in homes.

ELECTRICAL HEATINGElectrical Energy to Thermal Energy

Electricity is used to provide heat for

cooking, ironing and heating in homes.

Iron Room HeaterCooker

Oven Kettle

ELECTRIC MOTORElectrical Energy to Kinetic Energy

Electricity is used to provide useful mechanical

movement in homes.

Fan

Drill

Blender

Food Mixer

Blender

Washing Machine

WHAT CAN YOU DO TO FIND OUT

HOW MUCH ELECTRICAL

ENERGY YOU’RE USING AT HOME

ELECTICAL ENERGY & POWER AT HOME

1

2

Check the LABELS on the electrical appliance and write down its POWER RATINGS

The power ratings (also known as Power or Wattage) is in Watts (W)

The power ratings can also be calculated by the formula POWER = CURRENT x VOLTAGE

3

Keep track of the LENGTH OF TIME the electrical appliance is in use.

Remember to convert your time duration into seconds (s).

Use the formula ENERGY = POWER x TIMEThe unit of Electrical Energy is the Joule

1Check the LABELS on the electrical appliance

and write down its POWER RATINGS

The power ratings (also known as Power or Wattage) is in Watts (W)

CALCULATING ELECTICAL ENERGY & POWER

1Check the LABELS on the electrical appliance

and write down its POWER RATINGS

The power ratings can also be calculated by the formula POWER = CURRENT x VOLTAGE

But sometimes only CURRENT and VOLTAGE is

written on the appliance’s label!

Make sure that

the CURRENT is in Ampere &

VOLTAGE is in Volt


2Keep track of the LENGTH OF TIME the

electrical appliance is in use.

Remember to convert your time duration into seconds (s).


3 Use the formula ENERGY = POWER x TIME

The unit of Electrical Energy is the Joule

Make sure that the POWER is in Watt

& TIME is in Seconds


VOLTAGEENERGY CURRENT= X X TIME

ELECTRICAL ENERGY & POWERFORMULAE LIST

POWERENERGY

=TIME

VOLTAGEPOWER CURRENT= X

Electricity can be dangerous if it is not handled properly and safely.

ELECTRICAL FIREELECTROCUTION DEATH

ELECTRICAL SAFETYIN THE HOME

WHY ?WHAT ?

HOW ?

DAMAGED INSULATIONExposed live wire.

✴Accidentally touching the live wire can cause electric shocks.

✴Short-circuit leads to overheating and fire.

ELECTRICAL DANGERSIN THE HOME

WHAT ?OVERHEATING OF CABLES

Overheating and electrical fire.

✴Coiled and tangled long extension leads.

✴Overloading a mains socket.

WHY ?

HOW ?



WHAT ?DAMPED CONDITIONS

Water will conduct current.

✴Using electrical appliances in damp conditions will increase risk of electrocution.

WHY ?

HOW ?

KNOW YOUR

ELECTRICAL SAFETY

SYMBOLS


What are the safety precautions present in our homes ?

FUSE & CIRCUIT BREAKERS


The function of a fuse and circuit breaker is to limit the amount of current entering a circuit.

“FUSE”“CIRCUIT BREAKERS”


“FUSE”

A fuse will overheat and melts if the current entering the circuit is too high (exceed the fuse ratings).

Symbols of A Fuse


The fuse ratings is the maximum current that can pass through without melting the fuse.

The fuse ratings commonly available are:1A fuse, 2A fuse, 3A fuse, 5A fuse, 10A fuse and

13A fuse.

ELECTRICAL SAFETYIN THE HOME“FUSE RATINGS”

The correct fuse ratings for any electrical appliance can be determined by using the formula:

Select the nearest higher fuse ratings to be used in the electrical appliance.

CURRENTPOWER=VOLTAGE


“FUSE RATINGS”

WHAT WILL HAPPEN TO THE ELECTRICAL APPLIANCE IF WE PUT THE WRONG FUSE INTO THE PLUG ?

“FUSE & FUSE RATINGS”

TOO LARGE FUSE RATINGS USED

CORRECT FUSE RATINGS USED

TOO SMALL FUSE RATINGS USED

The appliance may overheat and be damaged as the fuse

allows too much current to enter.

The appliance will not work as the fuse allows too little

current to enter.

The appliance work normally as the fuse allows the correct amount of current to enter.



EARTH CONNECTION

Wiring that connects the metal body of any electrical appliances to the ground and stops it from becoming

‘live’.

“EARTH CONNECTION”

Symbol for Earth Connection


Some appliances do not have an earth connection. These appliances plugs have only two pins.

“DOUBLE INSULATION”

The outer case is made of plastic instead of metal, and acts as an extra layer of insulation around the wires.

Double Insulation Symbol


COLOUR-CODED WIRING


‘Live’ Wire

“COLOUR-CODED WIRING”

‘Neutral’ Wire

‘Earth’ Wire

Current ‘enters’ the mains circuit.

Has voltage of 240 V.

Brown colour.

Current ‘leaves’ the mains circuit.

Kept at 0 V.

Blue colour.

Green/yellow stripes.

A safety connection.


All electrical appliances are connected to the mains supply through a plug.

“THREE-PIN PLUG & ITS WIRING”

A three-pin plug needs to be wired correctly and fitted with the correct fuse in order to provide a safe

connection to the mains supply.


“THREE-PIN PLUG WIRING”


The earth wire is connected to the top pin (earth pin).

The live wire is connected to the right pin (fuse pin).

The neutral wire is connected to the

left pin.

SWITCH


Symbols of A Switch

“SWITCH”

Open Switch

Closed Switch

It can be used as a safety device to cut off the flow of current, in case of an electrocution accident.


The function of switches are to turn electrical appliances on or off.

“LOCATION OF FUSE & SWITCH IN AN ELECTRIC CIRCUIT”

Fuses and switches are

usually inserted along the ‘live’ wires

of a circuit.


EXAMPLE EXERCISE 1A light bulb is marked 120 V, 60 W.

How much energy does the bulb dissipate in one minute?

A small heater operates at 12V, 2 A.How much energy is used in 5 minutes?

5129/12/M/J/14 Q34

5129/12/O/N/13 Q36

A cell will deliver 3000 J of energy to a 2 W electric motor before the cell is exhausted. How long will the motor run?

5129/12/O/N/12 Q4

EXAMPLE EXERCISE 2The diagram shows an unsafe use of an extension cable.

What is the electrical hazard?

5129/12/O/N/11 Q11

A

B

C

D

the danger of burning out the appliances

the danger of melting the fuse

the danger of overheating the cable

the danger of the appliances not being earthed

EXAMPLE EXERCISE 3Some hairdryers do not have an earth wire. They are double insulated.

(a) Explain the meaning of double insulation.

5129/22/O/N/13 Q13

(b) Explain the importance of

(i) the hairdryer having a plastic case and not a metal case.

(ii) not handling the hairdryer with wet hands.

(c) Complete the sentence below about energy changes in a hairdryer.

Electrical energy is changed into ………….. energy and …………. energy.

EXAMPLE EXERCISE 4

An electric heater has a label attached to it, as shown in Fig.10.1.

(a) Use the information from Fig.10.1 to calculate the current in the electric heater when it is working normally.

5129/22/O/N/11 Q10

EXAMPLE EXERCISE 4(b) Another electric heater has a metal case. It has been wired

incorrectly because the live wire is touching the metal case.

5129/22/O/N/11 Q10

The live wire is fitted with a fuse and the heater has an earth connection. Explain how a person is protected from an electric shock when the heater is switched on.

EXAMPLE EXERCISE 5Fig.11.1 shows a lighting circuit.

5129/22/M/J/13 Q11

(a) Switch A is left open and switches B and C are closed.State which lamp or lamps, if any, will light.

EXAMPLE EXERCISE 5Fig.11.1 shows a lighting circuit.

5129/22/M/J/13 Q11

(b) The circuit contains a fuse. The fuse has a rating of 3 A.

Explain what is meant by the fuse rating.

EXAMPLE EXERCISE 55129/22/M/J/13 Q11

(c) When all the switches are closed to light both lamps, the current in lamp P is 0.25 A and the current in lamp Q is 0.35 A

(ii) The p.d across lamp P when lit is 240 V and the current in it is 0.25 A. Calculate the power of lamp P.

Fig.11.1 shows a lighting circuit.

EXAMPLE EXERCISE 6

Fig.1.1 shows a mains plug.

(a)Name:

(i)the wire labelled A

(ii) the component labelled B

5129/01/M/J/11 Q1

(b) State the colour of the neutral wire.

PRACTISE QUESTIONS

5129/12/O/N/14 Q32

Complete the following questions in pairs.

5129/12/O/N/14 Q39

Remember to raise your hands if you need help with the questions.

17 Practical Electricity

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