Science_Form_3

Chapter 4: Reactivity of Metals

Self-reflection

After studying this chapter, you are able to:

4.1 Variety of Minerals
Explain with examples minerals that are found in the Earth’s crust.
Identify elements found in natural compounds.
Explain with examples the characteristics of natural minerals and its uses in daily life.

4.2 Reactivity Series of Metals
Construct a reactivity series of metals based on its reactivity with oxygen and write the
word equation for the reactions.
Determine the position of carbon and hydrogen in the reactivity series of metals.

4.3 Extraction of Metals from their Ores
Communicate about the extraction of metals from its ore by illustrations.
Generate ideas on how to solve problems from unplanned mining activities to life on Earth.

Summative Practice 4

Answer the following questions:
1. The following are some of the minerals found in the Earth’s crust.

Iron Quartz Silver Bauxite Potassium
Galena Tin Hematite Limestone Diamond

(a) Classify the above minerals into two groups, namely elements and compounds.
Minerals in Earth’s crust

Elements Compounds

143

(b) Give one example of metal ore and name the elements combined in the metal ore.
2. Figure 1 shows tin ore.

Figure 1
(a) What is the scientific name of tin ore?
(b) State the substance used to extract tin from tin ore.
(c) Write the word equation for the reaction between tin and oxygen.

3. Mark '•' for the correct statement.

(a) The number of minerals in the Earth’s crust is the same as the number of elements. (   )
(b) Aluminium ore is a mineral compound in the Earth’s crust. (  )
(c) Calcium oxide that is used to reduce the acidity of soil is basic. (  )
(d) Carbon is used to form metal ores. (  )

4. (a) Name the substance that reacts with metals and is used to determine the position of
the metals in the reactivity series of metals.

(b) Potassium and sodium are kept in dark reagent bottles filled with paraffin oil.
Explain why.

5. Figure 2 shows the apparatus set-up of an activity to test the reaction of a metal towards
gas X.

Metal powder Glass wool
Potassium manganate(VII) crystals
Porcelain plate

Heat Heat

Figure 2


144

Chapter 4: Reactivity of Metals

(a) Name gas X.
(b) What is the function of potassium manganate(VII) in this activity?
(c) Explain the steps of the correct heating procedure in this activity.
(d) State the aim of this activity.
6. How can the position of carbon in the reactivity series of metals determine the method of
extraction of metals from their ores or metallic compounds?

Focus on HOTS

7. The construction of 3D (three dimensional) models are normally used in various fields.
You are required to make a 3D model of a blast furnace using the following materials:

•  Drinking straw
•  Empty mineral water bottle
•  Water
•  Cooking oil
•  Iron powder
•  Coke
•  Limestone powder
•  Transparent plastic bag
•  Motor
•  Blade of fan
•  Paper clips


Sketch your 3D model and explain. 

145

CChhaapptteerr

5 Thermochemistry

What is thermochemistry?
What are endothermic and
exothermic reactions?
What is the importance of
the concept of endothermic
and exothermic reactions in
daily life?

Let’s study

Endothermic and exothermic reactions
146

Science Gallery

Every chemical reaction is followed by a change in the form of energy.
When chemical reactions occur, chemical energy stored in the reactants is
converted to heat energy and released into the surroundings.

Thermochemistry is the study of heat changes when chemical
reactions occur. There are many applications of thermochemistry in our
daily life which include instant hot packs and instant cold packs as shown
in the photographs below.

Instant hot packs are used to
release heat into the surroundings.
The heat released by instant hot
packs can relieve muscle cramp
and increase the size of lumen in
the blood capillaries so that the rate
of blood circulation through these
capillaries is increased.

Instant cold packs are used to
absorb heat from the surroundings.
The heat absorbed by instant cold
packs can reduce the swelling of
wounds, get rid of heat from
inflamed tissues or body organs
and reduce the size of lumen in the
blood capillaries so that the rate of
blood circulation through these
capillaries is reduced and this
helps to stop bleeding.

Keywords Thermal equilibrium
Heat
Thermochemistry Temperature
Endothermic reaction
Exothermic reaction 147

5.1 Endothermic and Exothermic Reactions

When sodium is added to
water, the chemical reaction
that occurs is shown in
Photograph 5.1.

Name three forms
LIM of energy that are

released in this
chemical reaction.

What form of energy is
released or absorbed in
most chemical reactions?

Chemical reactions can be divided into two Photograph 5.1 Reaction
types based on the heat change that occurs between sodium and water
during the reactions. These are the exothermic
reactions and endothermic reactions.

SCIENCE INFO

The prefix ‘exo’ originates from the Greek word which means ‘outside’ while the suffix ‘thermic’ originates from
the Greek word which means ‘heat’. The prefix ‘endo’ originates from the Greek word which means ‘inside’.

RIFQI Sir, how can we identify whether the LIM
reaction shown in Photograph 5.1
148 is an exothermic or endothermic 5.1.1 5.1.2
reaction?

That’s easy. We only need to detect the change
in temperature of the water in the container. If the
water in the container becomes hot, the chemical
reaction is an exothermic reaction. If the water in
the container becomes cold, the chemical
reaction is an endothermic reaction.

Chapter 5: Thermochemistry

Now, I would like to ask a question. Name one measuring
device that is suitable for determining exothermic and
endothermic reactions. Then, explain your answer.

LIM A thermometer, sir. A rise in the reading of the

thermometer shows that heat is released into the

surroundings. This is an exothermic reaction. RIFQI

On the contrary, a drop in the reading of the

thermometer shows that heat is absorbed from

the surroundings. This is an endothermic reaction.

Very good! Let’s carry out Experiment 5.1 to compare
and contrast the exothermic and endothermic reactions.

Alright, sir.

LIM

RIFQI

LIM Ndeenodwvioc,eIhtewhromautilcidsrlseikauicetattoiobnaelssfo.kTrahdeqeAtsCnutththhee,ueteerorsehrrnmmortxemsviouuireponomnnrrimrsml.ndaoinNeeougenmtytnelgeayeodxsreraumios.neersttdTghrhaohrh,oseoonniswrws.psmeiTsisrwshiinm.cteAthahsrteaan.hraianitssetedshaeuxhreenerioainatnaehtdnhgetitinsidsermgroaretebiohcelasneadroestrimrhnabeecdegctdoitoronefnrato.thchmeteion. RIFQI

WwtPhhaahoeettonor,scgtohacredrpuisuhmi5hsa.m1issasicdhoadewlaerctndotiinon Vanedrycgoonotdra!sLteetx’sotchaerrrmy ociuat nEdxpenerdimotehnet r5m.1ictroeaccomtionpsar.e LIM
LIM Norcefhaleeemmneaeiercstghdarlyiernteehtaafoitcstariormen.s
Alright, sir.
Wnohramtfoarllmy roefleeeedargnosyis RIFQI

Srirseeraaa,cnhcttioieooxnwno?schatheonrwmwneiciinodPrehentnoifdytoogwtrhaheeprtmhhei5cr.1the LIM
RIFQI TtIcabiefnhehnmatechhetet’meposxowcmeetiaeachoattsrlaeunesrrryctemea.oaiinWinolccdetft,iehrrotehtenjhiuesaestcahwctctniaonohtantneteeaeo.menridIncfeidicocnttruhaotbrelhhredereeewrecdmaoctecaiimtncoctenitotrheeatihnenaisnhtecthceohtocaierotht,nactontah.nociegnnceetuarriirnniesder

SCIENCE INFO

Recall the relationship between
temperature and heat, and the
concept of thermal equilibrium
which you have learnt in Form 2.

5.1

Experiment 5.1

Aim
Compare and contrast the exothermic and endothermic reactions

Problem statement
What are the similarities and differences between the exothermic and endothermic reactions?

Hypothesis
An exothermic reaction is a chemical reaction that releases heat into the surroundings while
an endothermic reaction is a chemical reaction that absorbs heat from the surroundings.

5.1.2 5.1.3 149

Variables
(a) manipulated variable : Type of chemical substance
(b) responding variable : Final temperature reading
(c) constant variable : Volume of water
Materials
Sodium hydrogen carbonate powder, sodium hydroxide, ammonium chloride,
0.1M sodium hydroxide solution and 0.1M hydrochloric acid
Apparatus
Polystyrene cup, thermometer, spatula and measuring cylinder
Procedure

1. Measure and pour 50 ml of water into a polystyrene cup.
2. Leave the water in the polystyrene cup for 2 minutes.
3. Record the initial temperature reading of the water in the given table.
4. Add two spatulas of sodium hydroxide into the polystyrene cup and stir the mixture

until all the sodium hydroxide dissolves in the water as shown in Figure 5.1.

Thermometer

Spatula
Sodium hydroxide

Polystyrene cup

Water

Figure 5.1
5. Record the maximum or minimum temperature in the table.
6. Repeat steps 1 to 5 by replacing sodium hydroxide with ammonium chloride.
7. Measure and pour 25 ml of hydrochloric acid into a polystyrene cup.
8. Leave the acid in the polystyrene cup for 2 minutes.
9. Record the initial temperature of the acid in the given table.
10. Measure and pour 25 ml of sodium hydroxide solution into the polystyrene cup and

stir the mixture as shown in Figure 5.2.

Thermometer

Polystyrene cup

Sodium hydroxide
solution

Polystyrene cup Hydrochloric acid

150 Figure 5.2

5.1.3

Chapter 5: Thermochemistry

11. Record the maximum or minimum temperature in the table.
12. Repeat steps 7 to 11 by replacing sodium hydroxide solution with 2 spatulas of

sodium hydrogen carbonate powder.

Observations

Reactants Sodium Ammonium Hydrochloric Hydrochloric
hydroxide chloride salt acid and acid and
and water sodium sodium
and water hydroxide hydrogen
solution carbonate

Temperature before
reaction (°C)

Maximum
or minimum
temperature during
reaction (°C)

Type of reaction

Conclusion
Is the hypothesis of the experiment accepted? What is the conclusion of this experiment?
Questions

1. What is the operational definition for:
(a) the release of heat in this experiment?
(b) the absorption of heat in this experiment?

2. (a) What happens when the temperature shown on the thermometer is at maximum
or minimum?

(b) Explain your answer to question 2(a).
3. State the criteria used in this experiment to classify the reaction as:

(a) exothermic
(b) endothermic
4. List the exothermic reactions in this experiment.
5. List the endothermic reactions in this experiment.
6. (a) How can the accuracy of the maximum or minimum temperature be increased?
(b) Explain your answer to question 6(a).

5.1.3 151

Examples of Exothermic and Endothermic Reactions in Daily Life

Examples of exothermic and endothermic reactions in daily life are shown in Photograph 5.2.

Fireworks display Photosynthesis

Cake baking Respiration

Photograph 5.2 Examples of exothermic and endothermic reactions

Based on Photograph 5.2:
• which are exothermic reactions?
• which are endothermic reactions?

152 5.1.4

Chapter 5: Thermochemistry

Designing Materials Using the Concept of Exothermic and
Endothermic Reactions to Solve Problems in Daily Life

Carry out Activity 5.1 to design materials using the concept of exothermic and endothermic
reactions to solve problems in daily life.

Activity 5.1 • ICS, CPS,
STEM
To study engineering designs to solve problems in daily life
Instructions • Project-based
learning
1. Work in groups. activity
2. Gather information on the engineering design process to:

(a) produce materials to relieve muscle cramp

(b) produce an emergency lamp when there is a power failure

(c) design a container that can maintain high or low temperature

3. Write the information and research results obtained by your group in the form of
a folio.

5.1.5 153

Formative Practice 5.1

1. Define the following types of chemical reactions:
(a) Endothermic reaction
(b) Exothermic reaction

2. What is thermochemistry?

3. Why does our body temperature increase when performing vigorous physical activities?

4. (a) Name one example of a global phenomenon caused by exothermic reaction.
(b) Give one solution to the phenomenon mentioned in question 4(a).

5. (a) Name the reaction produced by materials to relieve muscle cramp.
(b) Explain your answer.

Summary

Thermochemistry

is
The study of heat changes that occur when chemical reactions take place

where

Heat is released into the surroundings Heat is absorbed from the surroundings
in
in
Exothermic reactions Endothermic reactions
in processes such as
Burning of paper, bomb in processes such as
explosion, respiration, Photosynthesis, cake baking, extraction
neutralisation of acid with alkali of iron from iron ore, dissolving
ammonium salt in water
which cause
A rise in temperature which cause
A drop in temperature
in the
Product of reaction in the
Product of reaction
154

Chapter 5: Thermochemistry

Self-reflection

After studying this chapter, you are able to:

5.1 Endothermic and Exothermic Reactions
Define endothermic and exothermic reactions.
Relate heat absorbed or released in a chemical reaction to endothermic and exothermic
reactions.
Carry out an experiment to compare and contrast endothermic and exothermic reactions.
Explain with examples exothermic and endothermic reactions.
Design materials using the concept of exothermic and endothermic processes to solve
problems in life.

Summative Practice 5

Answer the following questions:

1. There are two types of reactions: exothermic reaction and endothermic reaction. Match the
examples of processes with the correct type of reaction.

(a) Burning of petrol

(b) Photosynthesis

(c) Respiration Exothermic reaction
(d) Making bread Endothermic reaction
(e) Neutralisation

(f) Rusting of iron

2. Underline the correct answers.
(a) The burning of a candle is an exothermic reaction because heat is (released/absorbed).
(b) Exothermic reaction in the body (increases/decreases) the body temperature.
(c) Exothermic reaction is applied in instant (cold/hot) packs.
(d) Baking a cake is not an exothermic reaction because heat is (released/absorbed).

155

3. Solve the crossword puzzle below. (e) Across
(b) P (a) Study of heat
E
change when
(f ) (d) M chemical reactions
take place.
E T (b) Endothermic
reaction that
(a) T R occurs in plants.
(c) Exothermic
reaction that
occurs in animals.

(c) R

Down
(d) A device that measures change in temperature during exothermic and endothermic

reactions.
(e) Chemical reaction that absorbs heat from the surroundings.
(f) Chemical reaction that releases heat into the surroundings.

4. Figure 1 shows an apparatus set up to heat calcium carbonate.

Calcium Limewater
carbonate
Retort stand
Heat

Figure 1
Is the heating of calcium carbonate an exothermic reaction or an endothermic reaction?
Explain your answer.

156 5.1.1

Chapter 5: Thermochemistry

5. Differentiate the reaction between hydrochloric acid and sodium carbonate, and the
reaction between hydrochloric acid and sodium hydrogen carbonate.

6. How can the effects of global warming be reduced by the replanting of trees?
7. (a) Figure 2 shows a thermite reaction, that is the heating of iron(II) oxide, aluminium

powder and magnesium tape.

Figure 2
Is a thermite reaction an exothermic reaction or endothermic reaction? Explain your
answer.
(b) Figure 3 shows an application of a thermite reaction.

Figure 3
Describe the application of thermite reaction in Figure 3.

157

Focus on HOTS

8. Figure 4 shows an instant hot pack and an instant cold pack used in hospitals to relieve
muscle cramps and reduce the swelling of wounds.

PINAHSCOTKTANT PINCAOSCTLKADNT

hPerreess hPerreess

Figure 4

Using your creativity, modify and make an instant hot pack and an instant cold pack using
the following materials. Explain.

Two thin plastic Water
bags (size: small) Toothpick

Two thick plastic
bags (size: large)

Ammonium nitrate

Calcium chloride

158

THEME Energy and Sustainability
of Life
3

Solar cells are used to generate electricity. What is the importance of the generation
of electricity using solar energy in Malaysia?

According to the law in Malaysia,
the installation of smoke detectors in
buildings such as hospitals, hotels,
supermarkets and office buildings is
compulsory. Smoke detectors normally
contain a small amount of radioactive
substance. Name this radioactive
substance. What is the importance
of handling radioactive substances
effectively in daily life?

159

61CChhaapptteerr Electricity and
Magnetism

What are renewable
and non-renewable
energy sources?
What are the functions
of step-up and
step-down transformers?
How is the cost of
electricity consumption
calculated?

Let’s study

Generation of electricity
Transformer
Transmission and distribution of electricity
Calculating the cost of electricity consumption

160

Science Gallery

According to a report from the Malaysian Nuclear Agency,
Malaysia needs to have a nuclear power station in 2030. This power
station should generate electricity that is sufficient to meet the
electricity needs of our country. Do you agree or disagree with
having of this power station in Malaysia? Why?

(Source:http://www.utusan.com.my/sains-teknologi/inovasi/loji-
nuklear-negara-beroperasi-2030-1.146680)

MALAYSIA

# # ##

Where should nuclear power RIFQI
stations be built in our country?

Keywords Secondary coil Short circuit
Input voltage Electric shock
Power station Output voltage Kilowatt-hour (kWh)
Induced current National Grid Network Energy efficiency
Direct current Earth wire
Alternating current 161
Primary coil

6.1 Generation of Electricity

Various Energy Sources to Generate My Malaysia
Electricity
Malaysia is currently the leading
Did you know that our country, Malaysia is a country country in biomass industry in the
which is very successful in using various energy sources to Southeast Asian region.
generate electricity? What are the energy sources used in Sarawak and Sabah are two states
Malaysia to generate electricity? in Malaysia that have a variety and
a large amount of biomass. The
Electricity is generated through various energy sources. variety of biomass includes the
These different energy sources can be classified into two biomass of oil palm, forests, rubber
main groups, namely renewable energy sources and non- trees, garbage, rice husks and
renewable energy sources as shown in Figure 6.1. maize. Besides the generation of
Figure 6.2 shows renewable and non-renewable energy electricity, biomass is also used to
sources used in power stations in Malaysia. produce innovative products such
as building materials.

Energy sources

Renewable Non-renewable
energy sources energy sources

Definition Definition

Energy sources that can Energy sources that cannot
be replaced continually be replaced and will
and will never deplete. deplete.

Examples Examples Hybrid power station in Pulau Perhentian
Kecil, Terengganu (Energy source: Wind,
t Hydro energy t Nuclear energy Solar, Diesel)
t Wave energy t Coal
t Solar energy t Natural gas 6.1.1
t Tidal energy t Petroleum
t Wind energy
t Biomass energy
t Geothermal energy

Figure 6.1 Renewable and non-renewable energy sources
162

Chapter 6: Electricity and Magnetism

Bakun hydroelectric power station in
Sarawak (Energy source: Hydro energy)

Tuanku Jaafar power station in Negeri
Sembilan (Energy source: Natural gas)

Power stations
in Malaysia

Sultan Azlan Shah power station in Manjung,
Perak (Energy source: Coal)

Gelugor power station in Pulau Pinang
(Energy source: Diesel)

TSH Bio-Energy Sdn. Bhd. Biomass power
station in Sabah (Energy source: Biomass)

Figure 6.2 Power stations in Malaysia that use renewable
and non-renewable energy sources

6.1.1 163

Process of Generating Electricity

A generator is a device used to generate electricity. Look at Photograph 6.1 which shows an
example of a generator model.

Magnet Name two main components
that generate current in this
Coil of wire generator model.
Crank

Magnet

LED RIFQI

Photograph 6.1 Generator model

When the crank of the generator model is turned, a current known

as induced current is produced. The flow of this induced current

lights up the LED.

In 1831, a scientist named Michael

Faraday conducted a series of investigations

on the generation of electricity using Galvanometer

a magnetic field. Electric current is Galvanometer

produced by: 10 0 10
• Movement of the wire which causes the 20 20
Magnet
40 50
30 8
50 40 G 10 0 10
30 20 20

50 40 G 40
30 30
–+

61 –+ 50

magnetic field lines to be cut. Solenoid
is moved
A connecting wire or solenoid is moved

rapidly through the space between the

magnetic poles as shown in Figures 6.3 Connecting wire is 6

and 6.4. An induced current is produced moved

in the connecting wire or solenoid, and Figure 6.3 Figure 6.4
it flows through the galvanometer. The

pointer in the galvanometer deflects. Galvanometer Galvanometer
• Movement of the magnet which causes Magnet

the magnetic field lines to be cut. is moved 10 0 10
20 20
8
50 40 G 40
30 30
50 40
30–+ 50

A magnet is moved as shown in 10 0 10
Figures 6.5 and 6.6 so that the magnetic 20 20

G 40 50
30
–+

field lines are cut by the connecting wire Solenoid
or solenoid. An induced current is
6 1 Magnet is moved

produced in the connecting wire or

solenoid, and it flows through the Connecting wire

galvanometer. The pointer in the Figure 6.5 Figure 6.6
galvanometer deflects. 6.1.2

164

Chapter 6: Electricity and Magnetism

Activity 6.1 Inquiry-based activity

To study the production of electric current when magnetic field lines are cut by a copper wire

Materials
PVC insulated copper wire, connecting wire and cardboard tube with a coil of PVC
insulated copper wire (coil of wire/solenoid)

Apparatus
Bar magnet, U-shaped magnet and centre-zero galvanometer

Instructions
1. Connect the PVC insulated copper wire to the centre-zero galvanometer.
2. Move the copper wire downwards between the north and south poles of a U-shaped

magnet and then upwards as shown in Figure 6.3. Observe and record the deflection
of the galvanometer pointer.
3. Move the U-shaped magnet upwards and then downwards as shown in Figure 6.5.
Observe and record the deflection of the galvanometer pointer.
4. Connect the coil of PVC insulated copper wire to the centre-zero galvanometer.
5. Move the coil of wire as shown in Figure 6.4. Observe and record the deflection of
the galvanometer pointer.
6. Move the bar magnet as shown in Figure 6.6. Observe and record the deflection of
the galvanometer pointer.

Observations

Step Deflection of galvanometer pointer

2

3

5

6

Questions
1. What is detected by the galvanometer when the galvanometer pointer deflects?
2. What happens when a magnet moves relative to a copper wire or coil of copper wire?
3. What is produced by the cutting of the magnetic field lines by a copper wire or coil

of copper wire?

6.1.2 165

Activity 6.2

To build a simple generator that can light up an LED using magnets • ICS, ISS,
and a coil of wire STEM
Materials
PVC insulated copper wire, cellophane tape, connecting wires with • Innovation-
crocodile clips and LED based activity

Apparatus Coil of wire Magnadur magnet
Armature with axle, two magnadur magnets,
wooden plank (base) and C-shaped Cellophane 1 6
magnet holder tape to keep
Instructions commutator Commutator Carbon
1. Work in groups. in position brush
2. Construct a simple direct current (d.c.) LED

generator as shown in Figure 6.7. Ends of the coil of wire to
3. Make sure the axle is stationary. build commutator

Observe and record if the LED Magnadur magnet Axle
lights up.
4. Rotate the axle. Then, observe
and record if the LED lights up.
5. Present your findings.

Observation LED N Rotated
Condition of
axle Stationary Rotating S

LED

Figure 6.7 Simple d.c. generator
Questions
1. Mark ' ✓ ' for the true statement related to the cutting of magnetic field lines.

(a) When the coil of wire and magnet are stationary, the magnetic field
lines are cut.

(b) When the coil of wire moves inside the stationary magnet, the
magnetic field lines are cut.

(c) Current will only be induced when the magnetic field lines are cut.

2. How is induced current detected in this activity?
3. How is induced current produced by the d.c. generator?
4. State two forms of energy other than electrical energy produced in this activity.
5. State two advantages of LED as a lighting device compared to a filament bulb.

166 6.1.2

Chapter 6: Electricity and Magnetism

Electricity Generated at Power Stations

Study Figures 6.8 to 6.13. Observe how electricity is generated at power stations using various
sources of energy.

1 Power station using non-renewable energy sources such as diesel, natural gas
and coal.

Boiler Generator

Steam

Transmission tower

Turbine

Fuel Seawater SCIENCE INFO
Condenser
Mechanism Figure 6.8 Thermal power station A pylon is a tall metal structure to
Burning of which transmission cables carrying
fuel electricity are fixed so that they
are safely held high above the
ground.

Boiling water Steam rotates Generator produces
produces steam the turbine electricity

Energy Change Heat energy Kinetic energy Electrical energy
Chemical energy

2 Power station using solar energy. Solar panel

Mechanism Solar panels convert light energy from Figure 6.9 Power station
Sunrays the Sun into electricity using solar energy

Energy Change Electrical energy 167
Solar energy

6.1.2

3 Hydroelectric power station.

Water reservoir

Power tunnel

Generator

Transmission tower

Turbine

Water flows
into river

Figure 6.10 Hydroelectric power station

Mechanism Water flows from Flow of water Generator produces
high level to low rotates turbine electricity
High dam level
stores water
Kinetic energy Electrical energy
Energy Change
Gravitational
potential energy

4 Power station using wind Blade
energy.
Generator

Tower

Base
Figure 6.11 Power station using wind energy

Mechanism Wind moves Blades rotate Generator produces
Moving air blades turbine electricity
or wind
Electrical energy
Energy Change
Kinetic energy

168 6.1.2

Chapter 6: Electricity and Magnetism

5 Power station Uranium Steam Generator
using nuclear
fuel.

Pump Turbine Transmission
Nuclear reactor Pump tower

Seawater

Water Condenser

Figure 6.12 Nuclear power station

Mechanism Boiling water Steam rotates Generator
produces steam the turbine produces
Nuclear electricity
reaction

Energy Change Heat energy Kinetic energy Electrical energy
Nuclear energy

6 Power station Steam Turbine
using
biomass. Boiler Generator

Water Transmission
Burning of methane tower
Seawater
Pump
Generator produces
Methane Water Condenser electricity

Biomass Figure 6.13 Biomass power station

Mechanism Boiling water Steam rotates
Biomass produces steam the turbine
produces
methane

Energy Change Heat energy Kinetic energy Electrical energy
Chemical energy

6.1.2 169

Activity 6.3

To gather information and understand how electricity is generated at • ICS, ISS,
power stations STEM

Instructions • Discussion
1. Work in groups. activity

2. Gather information on how electricity is generated at power stations using various
sources of energy as shown in Figures 6.8 to 6.13:
(a) Process of generating electricity from various sources of energy
(b) Locations of power stations which use various sources of energy in Malaysia
3. Share the findings of your group discussion in class.

Direct Current and Alternating Current

Do you still remember the Do electric charges flow AIN
topic of electric current in through a conductor in
Form 2? one direction only or in
constantly changing directions?

Electric current is divided into two types, direct current (d.c.) and alternating current (a.c.).

Direct Current (d.c.)
Direct current is an electric current that flows in one direction only. Examples of devices that
use direct current are shown in Photograph 6.2.

(a) Torchlight (b) Calculator (c) Toy car

Photograph 6.2 Examples of devices that use direct current

Examples of generators or sources of electricity that produce direct current are shown in
Photograph 6.3.

(a) Solar cells (b) Accumulators (c) Batteries

Photograph 6.3 Examples of generators or sources of electricity that produce direct current

170 6.1.2 6.1.3

Chapter 6: Electricity and Magnetism

Alternating Current (a.c.)
Alternating current is an electric current that flows in constantly reversing directions. Look at
Photograph 6.4 which shows examples of devices that use alternating current.

(a) Bread toaster (b) Hair dryer (c) Air conditioner

Photograph 6.4 Examples of devices that use alternating current

Do most of the electricity generators in power stations produce d.c. or a.c.?

Cathode Ray Oscilloscope (C.R.O.) *(5:
7( .,
Cathode Ray Oscilloscope (C.R.O.) is an electronic device that is used to show
the differences in the shape of graph, direction of current and voltage change
for direct current and alternating current. For this, you are encouraged to gather
information on how to handle several control switches on the C.R.O. before
carrying out Activity 6.4. For this purpose, observe Photograph 6.5.

Y-gain Knob Intensity Control Knob
To change the To control the brightness
magnitude of the of the light spot on the
height of the light spot C.R.O. screen

Y-shift Knob Focus Control Knob
To adjust the position of To control the sharpness
the light spot vertically of the light spot on the
C.R.O. screen
X-shift Knob
To adjust the position of
the light spot horizontally

Direct Current/ Time-base Knob
Alternating Current
Switch To control the movement
of the light spot which
Selected according to the sweeps across the C.R.O.
type of input received screen horizontally

Photograph 6.5 Switches and control knobs on the C.R.O.

6.1.3 171

Activity 6.4 Inquiry-based activity

Using a Cathode Ray Oscilloscope (C.R.O.) to show the differences in the shape of graph,
direction of current and voltage change for direct current (d.c.) and alternating current (a.c.)

Material
Dry cell

Apparatus
Connecting wire, cell holder, C.R.O. and power source

Instructions
1. Switch on the C.R.O. and wait for a light spot to appear on the screen. Turn off the

time-base knob. Turn the intensity control and focus control knobs to adjust the
brightness and sharpness of the light spot shown in Figure 6.14.
2. Use the X-shift and Y-shift knobs to adjust the light spot so that it is at the zero
position in the centre of the screen as shown in Figure 6.14.
3. Turn on the time-base knob and observe the trace displayed on the screen as shown
in Figure 6.15.

Figure 6.14 Figure 6.15

4. Select the input switch to d.c. and adjust the Y-gain knob to 1 V/division. Turn off the
time-base knob.

5. Connect a dry cell to the Y-input (Photograph 6.6).

C.R.O.

Dry cell

Y-input

Photograph 6.6
172 6.1.3

Chapter 6: Electricity and Magnetism
6. Observe and record the trace displayed on the screen shown in Figure 6.16.

Determine the voltage across the dry cell by multiplying the displacement with the
value of Y-gain.
7. Turn on the time-base knob. Observe and record the trace displayed on the screen
as shown in Figure 6.17.

Figure 6.16 Figure 6.17

8. Repeat steps 5 to 7 but reverse the connection of the dry cell terminals. Observe and
record the trace displayed on the screen shown in Figure 6.18.

9. Turn on the time-base knob. Observe and record the trace displayed on the screen
as shown in Figure 6.19.

Figure 6.18 Power Figure 6.19
10. Select the input switch to supply
C.R.O.
a.c. and adjust the Y-gain
knob to 1 V/division. Turn Photograph 6.7 Y-input
off the time-base knob.
11. Connect a 2 V a.c. 173
terminal from the power
supply to the Y-input as
shown in Photograph 6.7.
12. Observe and record the
trace displayed on the
screen as shown in
Figure 6.20.

6.1.3

13. Turn on the time-base knob. Observe and record the trace displayed on the screen
as shown in Figure 6.21.

Figure 6.20 Figure 6.21

14. Repeat steps 10 to 13 but reverse the connection of the terminals of the power supply.
Observe and record the trace displayed on the screen as shown in Figure 6.22.

15. Turn on the time-base knob. Observe and record the trace displayed on the screen
as shown in Figure 6.23.

Figure 6.22 Figure 6.23

Observations Trace observed on the screen

Step
6
7
8
9
12
13
14
15

174 6.1.3

Chapter 6: Electricity and Magnetism
Questions
1. What is the function of the C.R.O. in this activity?
2. Compare and contrast the traces displayed on the screen as shown in steps 6 and 8.
3. What two inferences can be made based on your observations of the trace displayed

on the screen in steps 7 and 9?
(a) First inference
(b) Second inference
4. Based on your observations of the trace displayed on the screen in steps 12 and 14,
describe the change in voltage produced by the power supply. Explain your answer.
5. What are two inferences that can be made based on your observations of the trace
displayed on the screen in steps 13 and 15?
(a) First inference
(b) Second inference
6. Name the type of electric current supplied by the following energy sources:
(a) Dry cell
(b) Power supply

Solving Problems Related to Electricity My Malaysia
Supply in Life
‘Giant’ generators known as
Have you ever experienced disruptions of electricity supply gensets from TNB are used to
while at home or in school? If disruptions of electricity provide backup supply of electricity
supply is a big problem in your life, can you imagine the during disruptions.
lives of people living in rural areas without any electricity
supply? Let us carry out Activity 6.5 to make a model of a
generator that can produce electricity.

Activity 6.5

To create or innovate a model for generating electricity using turbines • ICS, CPS
and generators in rural areas without affecting the environment • Project-based

Instructions activity

1. Work in groups.
2. Create or innovate a model for generating electricity using turbines and generators in
rural areas without affecting the environment.

6.1.3 6.1.4 175

Examples of innovations to generate electricity.

Roof with solar cells Wireless electrical transmission and
distribution

Absorbs and changes solar energy to Changes electrical energy to radio
electrical energy without affecting the wave or microwave energy to be
environment transmitted and distributed without
wires to electrical devices. These
electrical devices then change the
radio wave or microwave energy
back to electrical energy.

3. Present your model or innovation using turbines and generators to generate electricity.

Formative Practice 6.1

1. What is meant by renewable energy sources and non-renewable energy sources?

2. Figure 1 shows three arrangements, P, Q and R with moving or stationary magnet and
coil of wire.

Coil remains stationary Coil moves towards the magnet Coil remains stationary

US US US

LED LED LED
Magnet moves
towards the coil Magnet remains Magnet remains
stationary stationary
Arrangement P Arrangement Q Arrangement R

Figure 1

(a) In which arrangement does the LED light up? Explain your answer.
(b) In which arrangement does the LED not light up? Explain your answer.

3. What is the function of a cathode ray oscilloscope or C.R.O.?

176 6.1.4

Chapter 6: Electricity and Magnetism

6.2 Transformer

Have you ever seen the device
shown in Photograph 6.8 in the area
where you live? What is the
importance of this structure in daily
life?

ADAM

Photograph 6.8 Transformer

Step-up Transformer and Step-down Transformer

A transformer is a device for changing the voltage of an alternating current (Va.c.). A simple
transformer is made up of laminated soft iron core which is wrapped by two insulated coils,
the primary coil and the secondary coil as shown in Figure 6.24.

Laminated soft
iron core

a.c. supply Load

Primary coil Secondary coil

Figure 6.24 Structure of a simple transformer
There are two types of transformers, the step-up transformer and the step-down
transformer as described in Table 6.1.

6.2.1 177

Table 6.1 Step-up transformer and step-down transformer

Step-up transformer Step-down transformer

Primary Secondary Primary Secondary
coil coil coil coil

Load Load

a.c. supply a.c. supply

Symbol Symbol

Primary voltage (input), Vp, across the primary Primary voltage (input), Vp, across the primary
coil is lower than the secondary voltage (output), coil is higher than the secondary voltage (output),
Vs, across the secondary coil. Vs, across the secondary coil.

Number of turns of the primary coil is less than Number of turns of the primary coil is more than
that in the secondary coil. that in the secondary coil.

Carry out Experiment 6.1 to construct and study the functions of simple step-up and
step-down transformers.

Experiment 6.1

Aim
To construct and study the functions of simple step-up and step-down transformers using
laminated soft iron core
Problem statement
What are the functions of step-up and step-down transformers?
Hypothesis
(a) In a step-up transformer, the secondary voltage (output) is higher than the primary

voltage (input).
(b) In a step-down transformer, the secondary voltage (output) is lower than the primary

voltage (input).
Variables
(a) manipulated variable : Number of turns of the secondary coil, Ns
(b) responding variable : Brightness of light bulb
(c) constant variable : Number of turns of the primary coil, Np
Materials
Connecting wire, insulated copper wire and light bulbs
Apparatus
a.c. power supply and laminated C-shaped soft iron core

178 6.2.1

Chapter 6: Electricity and Magnetism

Procedure
1. Wind 30 turns of wire around one arm of the
laminated soft iron core to form a primary coil as Safety
Precaution
shown in Figure 6.25.
2. Wind 15 turns of wire around the other arm of the Practise safety steps while
laminated soft iron core to form a secondary coil as handling power supply.

shown in Figure 6.25.
3. Connect the primary coil to an a.c. power supply. Then, connect light bulb P to the
primary coil and light bulb S to the secondary coil as shown in Figure 6.25.

a.c. power supply

INPUT : 220/240V A.C.50/60Hz OUTPUT; Max 12V AC/DC ST909T 7 8
0FF 6 9
D.C.
0N TOTAL LOAD 5 0
8 AMP. MAX. 11
4
A.C. VOLTS
3
2

Primary coil P
(30 turns)

Laminated C-shaped
soft iron core

Secondary coil
(15 turns)

S

Figure 6.25
4. Switch on the a.c. power supply and adjust its voltage to 2 V.
5. Observe and compare the brightness of the two bulbs.
6. Repeat steps 3 to 5 but using a primary coil with 30 turns and a secondary coil with

60 turns.

Observations Number of turns of Brightness of bulb
Number of turns of secondary coil, Ns PS
primary coil, Np
30 15
30 60

Conclusion
Is the hypothesis of the experiment accepted? What is the conclusion of this experiment?

6.2.1 179

Questions
1. Based on the results of this experiment:

(a) What is the effect on the brightness of the bulb if Np > Ns?
(b) What is the relationship between Vp and Vs if Np > Ns?
(c) What type of transformer is this?
2. Based on the results of this experiment:
(a) What is the effect on the brightness of the bulb if Np < Ns?
(b) What is the relationship between Vp and Vs if Np < Ns?
(c) What type of transformer is this?
3. What happens to the change in voltage of the alternating current in a transformer
if the difference between the number of turns in its primary coil and the number of
turns in its secondary coil is increased?
4. Why are the numbers of turns in the primary and secondary coils different in
all transformers?

Function of Transformer in Home SCIENCE INFO
Electrical Appliances
An induced current formed in
In Malaysia, the supply voltage of alternating current the iron core of a transformer
provided to our home is 240 V. Give one example of is known as the eddy current.
an electrical appliance at home that operates at 240 V The formation of the eddy current
alternating current without using a transformer. in a transformer will reduce the
efficiency of the transformer. Due
Most electrical appliances at home use transformers to this, a laminated iron core
such as those in mobile phone chargers (Photograph 6.9). is used to reduce eddy current
and increase the efficiency of the
transformer. A laminated iron core
is made up of layers of soft iron
and layers of insulators arranged
alternately.

Transformer

Photograph 6.9 A mobile phone charger Laminated
iron core
Is the transformer in a mobile phone charger a step-up
or step-down transformer? Let us carry out Activity 6.6 6.2.1 6.2.2
to discuss the transformers and their functions in home
electrical appliances.

180

Chapter 6: Electricity and Magnetism

Activity 6.6

To discuss the transformer and its functions in home electrical • ICS
appliances • Technology-

Instructions based activity

1. Work in groups.
2. Use various sources to gather information on transformers and their functions in
home electrical appliances.

Examples of the use of transformers in home electrical appliances

(a) Battery charger (b) Mobile phone charger (c) Ceiling fan
of a laptop regulator

3. Discuss the gathered information.
4. Present the outcome of the discussion using multimedia presentation.

Solving Problems Related to Transformers in Daily Life

Figure 6.26 shows an example of a home electrical appliance which is a ceiling fan regulator that
uses a step-down transformer. What is the formula used to determine the number of turns in
the secondary coil to lower the input voltage from 240 V to voltages ranging from 2 V to 10 V?

Step-down transformer

1 23 240 V 0V
04 a.c. 2V

55 4V
6V
40 8V
3 21 10 V

Figure 6.26 Ceiling fan regulator

6.2.2 6.2.3 181

Transformer Equation

The ratio of the primary voltage to the secondary voltage is equal to the ratio of the number of
turns of the primary coil to the number of turns of the secondary coil in a transformer. This
relationship can be written in the following formula:

Vp Np where Vp = input voltage of the primary coil or primary voltage
Vs Ns Vs = output voltage of the secondary coil or secondary voltage
= Np = number of turns of primary coil
Ns = number of turns of secondary coil

Example
Figure 6.27 shows a 40 V bulb connected to a 240 V power supply through a transformer.

240 V Np = 120 Ns 40 V

Figure 6.27

Find out the number of turns of the secondary coil, Ns, that is required for the bulb to light up
at normal brightness?

Solution

The bulb will light up at normal brightness if it is supplied with a voltage of 40 V.

• Output voltage, Vs = 40 V
• Input voltage, Vp = 240 V
• Number of turns in primary coil, Np = 120

Vp = Np
Vs Ns

240 = 120
40 Ns

Ns = 120 × 40
240
= 20

Number of turns in secondary coil, Ns = 20 6.2.3
182

Chapter 6: Electricity and Magnetism

Formative Practice 6.2

1. What is a transformer?
2. Underline the correct answers.

(a) Transformers only function using (direct/alternating) current.
(b) In a step-down transformer, the number of turns in the primary coil is (more/less)

than the number of turns in the secondary coil.
(c) A (step-up/step-down) transformer is used to change 25 kV to 250 kV.
(d) A (step-up/step-down) transformer is fixed in a radio.
3. State one example of a home electrical appliance which uses the following types of
transformers:
(a) Step-up transformer
(b) Step-down transformer
4. Figure 1(a) shows a transformer in a 5 V mobile phone charger connected to the 240 V
main power supply.

Transformer

Figure 1(a)
Figure 1(b) shows a circuit diagram of the transformer in the mobile phone charger.

240 V Np Ns = 10 5 V Mobile phone

Figure 1(b)
(a) Calculate the number of turns in the primary coil.
(b) Is the transformer in the mobile phone charger a step-up or step-down transformer?

Explain your answer.

183

6.3 Transmission and Distribution of
Electricity

Functions of the Components in the Electricity Transmission
and Distribution System

The electricity transmission and distribution system that connects a power station to your
house is shown in Figure 6.28.

Generators at power stations Alternating current from the power stations is then transmitted
produce alternating current with
a voltage of 11 kV or 25 kV. to a step-up transformer station (Bn). Here, the voltage of
the alternating current is increased to 132 kV, 275 kV or 500 kV

using a step-up transformer.

$ 132 kV/
275 kV/
11 kV/ 500 kV
25 kV

$ %Q

33 kV

( %W

240 V 415 V 415 V

House Office Hospital

184 KEY: C – National Grid Network
A – Power station D – Switch zone
E1 – Main substation
Bn – Step-up transformer station E2 – Branch substation
Bt – Step-down transformer station

Figure 6.28 Electricity transmission and distribution system

6.3.1

Chapter 6: Electricity and Magnetism

The high voltage alternating current is then transmitted through a network of transmission cables called
the National Grid Network (C) as shown in the photographs below.

500 kV alternating current transmission cables along 132 kV alternating current transmission cables at the
the North-South Highway. Tanjung Kling Power Station, Malacca

Transmission through At the end of the grid, the alternating current flows to a
long distances
switch zone (D) at the main substation (E1). This switch
& zone enables electricity to be sent to the branch
substation (E2) when needed. This switch zone is also
( used to enable specific power stations and grids to be
'
%W closed for maintenance works without disrupting the

33 kV electricity supply to consumers.

Heavy industrial area Main substation Switch zone

33 kV 11 kV

( %W At the main substation (E1) and branch substation (E2),
the alternating current is transmitted through a series of
Light industrial area step-down transformers (Bt) at the step-down
transformer station. The voltage of the alternating current
6.3.1 is reduced gradually to different voltage values to be
supplied to consumers according to their needs. For
example:
t IFBWZ JOEVTUSJBM BSFB BU 33 kV
t MJHIU JOEVTUSJBM BSFB BU 11 kV
t PGmDF
CVTJOFTT BOE SFTJEFOUJBM BSFBT BU 240 V

185

Impact on Residences Located Near the National Grid Network Pylons

High voltage alternating current is transmitted through transmission cables on the National
Grid Network pylons as shown in Photograph 6.10. A strong electromagnetic field is produced
by the high voltage alternating current and can be detected in the surrounding areas close to the
pylons. Observe the effect of this electromagnetic field by using a compass. What happens to
the position of the compass needle?

My Malaysia

Go to the following websites:
https://www.tnb.com.my/
https://www.sesb.com.my/
http://www.sarawakenergy.com.my/
What are the facilities provided by
Tenaga Nasional Berhad (TNB),
Sabah Electricity Sdn. Bhd. (SESB)
and Sarawak Energy Berhad
(Sarawak Energy) to consumers
in Malaysia?

Photograph 6.10 Transmission cables
on the National Grid Network pylons

Let us carry out Activity 6.7 to discuss the impact of the National Grid Network pylons on
nearby residences.

Activity 6.7

To discuss the impact of the National Grid Network pylons on nearby • ICS, CPS
residences • Discussion

Instructions activity
1. Work in groups.
2. Gather information related to the issues of Photograph 6.11 Residences located
near a National Grid Network pylon
the impact on residences located near the
National Grid Network pylons as follows:
(a) Strength of electromagnetic field close

to the National Grid Network pylons
(b) The impact of electromagnetic field on

human health perceived by locals and
confirmed by medical experts
(c) Ways to solve the issues regarding the
electromagnetic field on residential areas
close to the National Grid Network pylons
3. Share the outcome of your group discussion
in class.

186 6.3.1

Chapter 6: Electricity and Magnetism

Electrical Wiring System in Malaysia BRAIN
TEASER
The electrical wiring system in Malaysia consists of
two different types, one-phase wiring (or single-phase) Tenaga Nasional Berhad (TNB)
and three-phase wiring as shown in Figures 6.29 and 6.30. suggests that users of single-
phase wiring who use more
Phase 1 than 10 kW or 50 A to switch
to three-phase wiring. Compare
P and contrast the importance of
single-phase wiring and three-
phase wiring in electricity usage.
Does your family accept TNB's
suggestion? Give your reasons.

P P: Peak
One cycle

The single-phase wiring is only suitable and Websites
stable enough for electricity usage not exceeding
10 kW or 50 A, such as in rural residential areas. Ways to identify the types of
electrical wiring
Figure 6.29 Single-phase wiring
http://links.and l17.com/BT_
Phase 1 Phase 2 Phase 3 Science _187

P PP

PP P
One cycle P: Peak

In commercial and industrial areas where
electricity usage is more than 10 kW or 50 A,
the three-phase wiring which is more stable and
reliable is used.

Figure 6.30 Three-phase wiring

6.3.2 187

Electricity Supply and Wiring System in Homes

Figure 6.31 shows an example of electricity supply and wiring system in homes.

Electric wires from the main cable that Neutral Live wire
are connected to homes are made up of: wire
t -JWF XJSF BU 7 5A
t /FVUSBM XJSF BU 7 15 A

Main fuse box with one Heating circuit
main fuse 30 A

Electric meter Air conditioning
t .FBTVSFT UIF UPUBM VOJUT PG circuit
30 A
electricity used

Main switch
t $POUSPMT UIF UPUBM DVSSFOU nPXJOH

through the circuit in the house

Consumer unit &BSUI -FBLBHF $JSDVJU #SFBLFS
and fuse box &-$#

t #SFBLT UIF DJSDVJU XIFO UPP NVDI

DVSSFOU nPXT UISPVHI JU

Miniature Circuit Breaker (MCB)
t 4FQBSBUFT UIF mOBM DJSDVJU UP

different electrical appliances

KEY: -JWF XJSF
/FVUSBM XJSF
Earth wire

Earth wire

Photograph 6.12 Earthing earth wire 6.3.2

188

Chapter 6: Electricity and Magnetism

-JHIUJOH DJSDVJU JT NBEF VQ
PG MJWF XJSF BOE OFVUSBM
wire.

Lighting circuit

Two way switch Power circuit is made up
PG MJWF XJSF
OFVUSBM XJSF
and earth wire.

Socket

Socket

Socket 189

Figure 6.31 Example of electricity supply and wiring system in homes
6.3.2

3-pin Plugs and 2-pin Plugs
Compare and contrast the structures of the 3-pin plugs and 2-pin plugs shown in Photograph 6.13.

Hong Kong India North America Japan Europe

Photograph 6.13 3-pin plugs and 2-pin plugs used in different countries

The 3-pin plug and 2-pin plug used in our country are explained in Table 6.2.

Table 6.2 3-pin plug and 2-pin plug in the wiring system in homes

3-pin plug 2-pin plug

Electrical appliances such as electric kettles and Electrical appliances such as hair dryers and
irons obtain electricity from the sockets on the electric toothbrushes obtain electricity from the
walls through 3-pin plugs. sockets on the walls through 2-pin plugs.

The live wire, neutral wire and earth wire connected to 2-pin and 3-pin plugs are required to follow
the international colour code for wiring shown in Figure 6.32 to ensure the safety of electricity use.

Earth wire (yellow 13 A Fuse
and green stripes)
Live wire
Neutral wire (brown)
(blue)

Figure 6.32 International colour code for wiring
190 6.3.2

Chapter 6: Electricity and Magnetism

Safety Components in the Wiring System in Homes

In the wiring system in homes, some of the safety components are shown in Photograph 6.14.

(a) Switch (b) 3 A, 5 A, 10 A and (c) Earth Leakage Circuit
13 A fuses Breaker (ELCB)

(d) Miniature circuit (e) Earth wire (f) Lightning conductor
breaker (MCB)

Photograph 6.14 Safety components in the wiring system in homes

Fuse Filled with nitrogen or Fuse wire
Structure of Fuse quartz particles
A fuse, as shown in Figure 6.33, is
a fine and short wire that heats up Metal contact
easily and melts when the current cap
flowing through it exceeds the value
of the fuse. If the wire of the fuse $
melts, the electricity supply will be
cut off. Value of fuse Glass or porcelain
casing
6.3.2 6.3.3
Figure 6.33 Structure of a fuse

191

Cartridge Fuse and Replaceable Wire Fuse

The two types of fuses usually used are cartridge fuse and replaceable wire fuse (fuse installed
with a fuse wire) as shown in Figure 6.34.

Glass casing Metal cap Fuse wire

(a) Cartridge fuse (b) Replaceable wire fuse
What is the maximum current
Figure 6.34 Two types of fuses that can flow through a 3-pin
plug installed with a 13 A fuse?
All fuses including cartridge fuses and replaceable wire fuses
function as electrical safety devices in circuits or electrical RIFQI
appliances to protect the wires and appliances from any
excessive current flow. BRAIN
TEASER
Determining the Value of a Fuse
Why is an electric kettle fixed
The value of a fuse is the maximum value of current that can with a 3-pin plug that has a
flow through the fuse without causing its fuse wire to melt. For 13 A fuse?
example, a 5 A fuse wire allows a maximum current of 5 A to
flow through it. Some common fuse ratings are 1 A, 2 A, 3 A,
5 A, 10 A, 13 A, 15 A and 30 A.

Choosing the value of a fuse depends on the value of the
maximum current that flows through a circuit or electrical
appliance. The fuse to be used should have a value which is
slightly higher than the maximum current that flows through
a circuit or electrical appliance in normal operating conditions.
For example, an electric kettle that uses a maximum electric
current of 11.34 A should be installed with a 13 A fuse.

Activity 6.8

To discuss the safety components in the wiring system in homes • ICS

Instructions • Discussion
1. Work in groups. activity

2. Identify and discuss the following:
(a) Functions, types and values of fuses
(b) Function of an earth wire
(c) Function of circuit breakers, namely Miniature Circuit Breaker (MCB) and Earth
Leakage Circuit Breaker (ELCB)
(d) Lightning conductor and switch
3. Use various sources to gather the required information.
4. Present the outcome of the discussion using multimedia presentation.

192 6.3.3