Express notes science form 3

All Rights Reserved ©2012 Ng Chee Kin
Written By
Ng Chee Kin
B.Sc.(Hons.), MBA
ngcheekin@gmail.com
mrcheekin@blogspot.com.au

iii
EXPRESSEXPRESSEXpresS��
CHAPTER 1
Respiration
1.1 Human Breathing Mechanism
1. The human respiratory system:
2. The air flow during inhalation:
Nose Trachea Bronchus Bronchiole
Alveolus
3. The air flow during exhalation:
Alveolus Bronchiole Bronchus
Trachea Nose
1.2 Transport of Oxygen in the Human Body
1. The oxygen dissolves in the moist lining of the
alveolus and then it diffuses into the blood
capillaries.
2. In the blood capillaries, oxygen will combine
with haemoglobin in the red blood cells to form
oxyhaemoglobin.
Lung
Bronchioles
Trachea
Bronchus
(plural: bronchi)
Bronchiole
Alveolus
(plural: alveoli)
Blood capillaries
around the alveoli
1.3 The Importance of a Healthy Respiratory
System
1. Chemical substances which are harmful to the
respiratory system are:
(a) nicotine, tar and carbon monoxide from
cigarette smoke
(b) sulphur dioxide, nitrogen oxide, carbon
monoxide, asbestos dust, coal dust and
hydrocarbons from vehicles and factories.
2. Tar and asbestos dust are carcinogenic, which
means they can cause lung cancer if inhaled
excessively.
3. Bacteria, viruses and other microorganisms
produce toxins which cause illnesses.
4. We need to improve the quality of air in order
to preserve healthy respiratory system.
CHAPTER 2
Blood Circulation and Transport
2.1 Transport System in Humans
1. The human heart:
Oxygen
Lungs
Heart
Other
body
cells
Movement of oxygen
Movement of oxygenated blood
Movement of deoxygenated blood
Haemoglobin
Oxyhaemoglobin
Key:
Oxygenated blood returns
to the heart
Oxygen enters blood in
the lungs
Deoxygenated blood
pumped out of the heart
Oxygenated blood
pumped out of the
heart
Deoxygenated blood
returns to the heart
3. When oxyhaemoglobin reaches the body cells, it
breaks down and releases oxygen.
4. The oxygen is then absorbed by the body cells
for cellular respiration.
Septum
Vena cava
Semilunar
valves
Right
atrium
Tricuspid
valve
Right
ventricle
Aorta
Pulmonary artery
Left atrium
Bicuspid
valve
Left
ventricle
Pulmonary
vein
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Deoxygenated blood Oxygenated blood
AortaPulmonary artery
Vena cava
Right atrium
Vena cava
Tricuspid
valve
Right
ventricle
Cardiac muscle
Pulmonary
vein
Semilunar
valves
Left atrium
Bicuspid
valve
Septum
Left ventricle
2. Functions of the heart:
(a) Pumps blood to all parts of the body.
(b) Transports nutrients and oxygen to the body
cells.
(c) Transports carbon dioxide and waste
materials from the body cells.
3. Types of blood vessels:
Characteristic Artery Vein Capillary
Structure
Size of lumen Small Large Very small
Thickness of wall Thick, muscular, elastic Thin, less elastic,
muscular
Only one cell thick and
not muscular
Speed of blood flow Rapid Slow Very slow
Blood pressure Very high pressure Low pressure Very low pressure
Presence of valves No except at aorta and
pulmonary artery
Yes No
5. Double circulatory system:
(a) Deoxygenated blood is pumped from the
heart to the lungs and oxygenated blood
flows back again to the heart.
(b) Oxygenated blood is pumped from the heat
to the rest of the body and deoxygenated
blood flows back again to the heart.
6. Human blood transports many substances in our
body.
Substance
transported
From To
Oxygen (in
the form of
oxyhaemoglobin)
Lungs All body
cells
Carbon dioxide All body cells Lungs
Digested food
(glucose, amino
acids)
Small
intestine
Liver and
all body
cells
Waste materials
(such as urea)
Liver and
cells
Kidneys
Hormones Endocrine
glands
Target
organs
2.2 Human Blood
1. Human blood consists of:
(a) 55% plasma
(b) 45% blood cells and platelets
2. Types of blood cells:
Type Function
Red blood cells Carries oxygen from the
lungs to the body cells
White blood
cells
Defends the body against
diseases
Platelets Helps in blood clotting
3. Functions of blood:
(a) Transports gases and dissolved substances
(b) Protects the body against diseases
(c) Maintains the body temperature at 37o
C
Smooth
muscle
Endothelium
Lumen
Connective
tissue
Connective
tissue
Smooth
muscle
Endothelium
Lumen EndotheliumLumen
4. Path of blood flow in the circulator system:
Deoxygenated
blood
Right
atrium
Right
ventricle Internal organs
(for example,
liver, gut)
Rest of the body (for
example, head, arms,
legs)
Left
ventricle
Left
atrium
Oxygenated
blood
Lung
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4. Compatibility of blood groups:
Recipient’s blood
Donor’s group
blood group
A B AB O
A    
B    
AB    
O    
5. Universal donor is a person with blood group O.
6. Universal recipient is a person with blood group
AB.
2.3 Transport System in Plants
1. The transport system in plants is called the
vascular system.
2. There are two main vascular tissues:
(a) Xylem- transports water and mineral salts
from the roots to the leaves
(b) Phloem- transports glucose from the leaves
to all parts of the plants
3. Xylem and phloem are found in the vascular
bundle.
4. Transpiration is the process by which plant loses
water, in the form of water vapour.
5. Transpiration happens through the stomata
(singular: stoma), tiny pores on the leaves of
the plant.
6. Factors that affect the rate of transpiration:
(a) Light – the brighter the light, the greater
the rate of transpiration.
(b) Temperature – the higher the temperature,
the greater the rate of transpiration.
(c) Humidity – the lower the humidity, the
greater the rate of transpiration.
(d) Wind – the faster the movement of air, the
greater the rate of transpiration.
7. Transpiration helps plants to absorb and transport
water and minerals.
CHAPTER 3
Excretion
3.1 Human Excretion
1. Excretion is a process of eliminating waste
products from the body.
2. The organs responsible for removing waste
products are called the excretory organs.
3. The waste products removed from the body are
called the excretory products.
Excretory organ Excretory products
Skin Water, mineral salts, urea
Lungs Water, carbon dioxide
Kidneys Water, mineral salts, urea
4. Excretion helps to maintain the balance of water
content, chemical composition and pH in the
body system.
3.2 The Urinary System in Humans
Vena cava
Renal
vein
Right
kidney
Urethra
Aorta
Adrenal
gland
Renal
artery
Left
kidney
Ureters
Urinary
bladder
Xylem
Phloem
Cross section of leaf
Cross section of stem
Cross section of root
Epidermis
Phloem
Xylem
pith
vascular
bundle
Root hair
Cortex
Endodermis
Xylem
Phloem
Epidermis








Cortex
Medulla






Cortex
Medulla
Pyramid
Ureter
Pelvis
Renal vein
Renal artery
1. The human urinary system consists of: kidney,
ureter, bladder and urethra.
2. Functions of kidneys:
(a) To filter blood.
(b) To remove urea, excess mineral salts and
water to form urine.
(c) To control the balance of water and chemical
in the body.
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3. Kidney failure happens when the kidneys of
a person unable to perform their functions
properly.
4. Kidney failure can be treated through dialysis
or kidney transplant.
5. Dialysis is a method used to filter and remove
waste products from the blood of a patient.
3.3 Excretion in Plants
1. Plants excrete waste products mainly through
simple diffusion.
2. Excretion in plant is mainly done through the
cell wall and stomata.
3. Mineral salts such as calcium carbonate and
calcium oxalate are retained in the plant as
crystals.
4. Minerals such as silicon salts are deposited in the
leaves to strengthen the leaf blade.
5. Nitrogenous waste products are removed when
plants shed their leaves, flowers or bark.
6. Most nitrogenous wastes are very poisonous.
7. Some excretory products of plants are useful
to humans such as: morphine, opium, cocaine,
tannins and oils.
CHAPTER 4
Reproduction
4.1 Understanding Sexual and Asexual
Reproduction
1. Reproduction is a process of producing new
individuals by living organisms.
2. Importance of reproduction:
(a) To increase the number of individuals of the
same species.
(b) To ensure certain species does not become
extinct.
3. Types of reproduction:
Vas deferens
Urethra
Penis
Scrotum
Testis
Seminal
vesicle
Prostate
gland
Seminal vesicle
Prostate gland
Epididymis
Penis
Testis Scrotum
Urethra
Vas deferens
4.2 Male Reproductive System
Organ Function
Testis (plural:
testes)
• Produces sperms (the male
gametes)
• Produces male sex hormones
Scrotum • Holds and protects the testes
Sperm duct
(vas deferens)
• Transports sperms from the
testes to the urethra inside
the body
Urethra • Allows sperms to flow out of
the body
Penis • Transfers semen into vagina
during copulation
Seminal
vesicles
• Secrete fluid which contains
nutrients for the sperms
1. Sperm:
(a) It is the male sex cell.
(b) It is produced by the testes.
(c) It is also the smallest cell in the males’
body.
(d) It is shaped like a tadpole, which has a head,
neck, middle piece and tail.
(e) The head contains a nucleus which has
genetic material.
(f) The tail helps the sperm to move or swim in
the female reproductive system.
2. Males reach puberty at 12 to 14 years old, which
is later than girls.
3. There are physical, emotional and physiological
changes during puberty.
4. The testes start to produce sperm and male sex
hormones during puberty.
Reproduction
AsexualSexual
(Involving the male and the female gametes)
Binary fission
(bacteria)
Regeneration
(planaria)
Budding
(yeast)
Spore formation
(moss, ferns and fungi)
Vegetative
reproduction
Animals
(sperm and ovum)
Plant
(pollen grain
and ovule)
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4.3 Female Reproductive System
Oviduct (Fallopian tube)
Ovary
Uterus
Cervix
Vagina
(c) Fertile phase / ovulation phase (day 12 to 16)
(d) Premenstrual phase (day 17 to 28)
6. Women of about 50 years of age undergo
menopause when their menstruation stops.
4.5 Fertilisation and Pregnancy
1. Fertilisation is the fusion between the sperm and
the ovum.
2. Development of an embryo into a foetus until
birth:
Sperm Ovum
Zygote
Embryo
Foetus
Baby
Fertilisation
Implantation
Childbirth
Oviduct (Fallopian tube)
Cervix
Urethra
Vagina
Uterus
Ovary
1. Ovum (plural: ova):
(a) It is the female sex cell.
(b) It is produced by the ovary.
(c) It is the largest cell in the females’ body.
(d) It is spherical in shape, which contains a
nucleus and cytoplasm.
(e) The nucleus contain genetic material.
(f) It cannot move by itself.
4.4 Menstrual Cycle
1. Menstrual cycle is the changes in a woman’s ovary
and uterus over 28 days.
2. Menstrual cycle involves ovulation and
menstruation which happen regularly each
month.
3. Ovulation happens when an ovary releases a
mature ovum.
4. Menstruation is the shedding of the uterine wall
and blood through the vagina.
5. Menstruation can be divided into four stages:
(a) Menstruation phase (day 1 to 5)
(b) Repair phase (day 6 to 11)
Organ Function
Ovary • Produces ova (the female
gametes)
• Produces female sex hormones
Fallopian
tube (oviduct)
• Place of fertilisation
Uterus
(womb)
• Place for the implantation of
zygote
• Place where the foetus
develops and grows
Cervix • Widens during childbirth
Vagina (birth
canal)
• Place where the sperms are
deposited during copulation
• Baby is born through this
birth canal
Ovary produces an ovum (ovulation)
Fallopian tube
The ovum is fertilised (fertilisation)
Embryo attaches to
uterine wall (implantation)
Embryo moves
towards uterus
Uterus
Ovary
An embryo is formed
A zygote is formed
Eight-cell
stage
Four-cell
stage
Two-cell
stage
4.6 Importance of Prenatal Care
1. Pregnant women need to take enough nutritious
food and have a balanced diet.
2. Pregnant women should avoid smoking, taking
alcohol or drugs.
4.7 Importance of Research in Human
Reproduction
1. Sterility (infertility) is the inability to produce
children.
2. Methods to overcome sterility:
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2. Germination happens when the embryo grows
into a seedling.
3. Seeds need air, water and suitable temperature
to germinate.
4.12 Vegetative reproduction in Flowering
Plants
1. Vegetative reproduction is a method of producing
new plants from any vegetative parts of the
parent plant.
2. Vegetative reproduction is an asexual
reproduction.
3. Vegetative parts that can reproduce are: stem,
leaf and root.
4. Tissue culture and stem cuttings are techniques
used to produce new plants.
CHAPTER 5
Growth
5.1 Human Growth Pattern
1. Growth is an irreversible and permanent process
in living things.
2. Growth in humans can be determined by
measuring the height and weight.
3. Growth curve is divided into five stages:
(a) Infancy (d) Adulthood
(b) Childhood (e) Old age
(c) Adolescence
(a) Drug treatment (such as hormones)
(b) Surgery
(c) In vitro fertilisation (IVF)
3. Methods for birth control (contraception):
(a) Contraceptive pills
(b) Rhythm method (natural method)
(c) Using a condom
(d) Using a diaphragm
(e) Intrauterine contraceptive device (IUCD)
(f) Vasectomy – sperm ducts cut and tied
(g) Ligation (tubectomy) – oviducts cut and tied
4.8 Sexual reproductive System of Flowering Plants
1. Struture of a flower:
Anther Filament
Stamen
Flower
Pistil
Ovary Stigma Style
Pollen grain Ovule
Petal
Anther
Filament
Stamen
Nectary
Receptacle
Pedicel
Sepal
Stigma
Style
Pistil
Ovary
Ovule
Structure Function
Ovary To protect the ovule
Ovule Contains ova (the female gametes)
Anther Contains pollen grains (the male gametes)
Filament To support anther
4.9 Pollination
1. Pollination is the transfer of pollen grains from
the anther to the stigma.
2. Self-pollination and cross-pollination:
4. Agents of pollination:
(a) Wind (c) Insects
(b) Animals (d) Water
4.10 Development of Fruits and Seeds in Plants
1. Fertilisation occurs when the male gamete fuses
with the ovum in the ovule.
2. A zygote is formed when the ovum is fertilised
by the male gamete.
3. After fertilisation, the ovule will develop into a
seed and the ovary become the fruit.
4.11 Germination of Seeds
1. A seed is made up of an embryo and a food
store wrapped in a testa (seed coat).
Infancy
Slow
growth Rapid
growth
Rapid
growth
Minimal
growth Negative
growth
0 3 13 20 65
Age (years)Height(cm)
Adolescence
Childhood
Old age
Adulthood
Structure Function
Sepal To protect flower during the bud stage
Petal To attract insects or animals
Stamen The male reproductive part
Pistil The female reproductive part
Stigma To receive pollen grains
Style To support stigma
Stigma
AntherPollen grains
Pollen grains
One plant Another plant of
the same species
Key:
Self-pollination Cross-pollination
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CHAPTER 6
Land and Its Resources
6.1 Minerals in the Earth’s Crust
1. Minerals are solid elements or compounds found naturally.
2. Elements present in various minerals:
Oxide Carbonate Sulphide Silicate
Element Cassiterite Haematite Calcite Malachite Galena
Iron
pyrite
China
clay
Calcium
silicate
Tin 
Iron  
Calcium  
Copper 
Lead 
Aluminium 
Silicon  
Oxygen      
Carbon  
Sulphur  
3. Properties of minerals:
Properties Description
Hardness Most mineral are hard
Solubility
in water
Most minerals are insoluble in
water
Action of
heat
• Most metal oxides are stable
• Metal sulphides break down
into metal oxide and release
sulphur dioxide gas
6.2 Reactions Between Metals and Non-metals
1. Metals react with non-metals at different rates
to form stable compounds:
(a) Metals react with oxygen to form metal
oxide
(b) Metals react with sulphur to form metal
sulphide
Metal
Reaction
rate with
oxygen
Reaction
rate with
sulphur
Magnesium Very fast Very fast
Aluminium Very fast Very fast
Zinc Fast Fast
Iron Fast Fast
Copper Slow Slow
6.3 Silicon Compounds
1. Silicon is the second most abundant element in
the Earth’s crust.
2. Silicon always exists in the form of compounds
such as silicas and silicates.
3. Silica is silicon dioxide, which consists of silicon
and oxygen.
4. Silicate is made up of silicon, metal and oxygen.
5. Properties of silicas and silicates:
(a) Insoluble in water
(b) Do not react with acid
(c) Do not break down when heated
(d) Very stable and are not eroded easily
6.4 Calcium Compounds
1. Properties of calcium carbonate:
(a) Insoluble in water
(b) Reacts with dilute acids to produce salt, water
and carbon dioxide
(c) Breaks down into calcium oxide and carbon
dioxide when heated
2. Quicklime (calcium oxide) is formed when calcium
carbonate is heated strongly.
3. Slaked lime (calcium hydroxide) is formed when
calcium oxide is added with some water.
4. Limewater (calcium hydroxide solution) is formed
when slaked lime is added with more water.
6.5 Natural Fuel Resources and Their Importance
1. Fossil fuels include petroleum, natural gas and
coal.
2. Petroleum:
(a) Formed from organism remains buried in
sediment under heat and high pressure.
(b) It contains many types of hydrocarbons which
can be separated by fractional distillation.
(c) The components of petroleum produced by
fractional distillation are called fractions (or
distillates).
(d) Different fractions are obtained due to
different boiling points.
• the greater the boiling point, the darker
the colour of the fractions
• the greater the boiling point, the more
viscous the fractions
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CHAPTER 7
Electricity
7.1 Electrostatics
1. Electrostatics is the study of static electrical
charges.
2. Electrical charges can be produced through
friction between two objects.
3. Matters are made up of small particles called
atoms.
Structure of an atom
4. An atom has two charged particles:
(a) Electrons, which have a negative charge (–)
(b) Protons, which have a positive charge (+)
5. Neutrons in an atom have no charge because
they are neutral.
6. An atom becomes positively charged when it
loses electrons.
7. An atom becomes negatively charged when it
gains electrons.
7.2 Electricity
1. Electricity is a form of energy. It is also called the
electrical energy.
2. Electrical energy can be generated by generators
and electric cells.
3. Current, voltage and resistance:
(a) Current
– the rate of flow of charges.
– flows from the positive terminal to the
negative terminal of a battery.
The flow of electric current and electron
(b) Voltage
– the electrical force needed to move
electrical charges from one point to other
in a conductor.
(c) Resistance
– characteristic that resists the flow of electric
current in a conductor.
7.3 Electric Current, Voltage and Resistance
1. Measuring current (symbol: I):
– connect an ammeter in series with other
electrical components in a circuit.
– the deflection of the pointer of the ammeter
shows the value of current flowing through
the components.
– the SI unit for electric current is ampere
(symbol: A).
2. Measuring voltage (symbol: V):
– connect a voltmeter in parallel to other
electrical components in a circuit.
– the deflection of the pointer of the voltmeter
shows the value of voltage across the
components.
– the SI unit for voltage is volt (symbol: V).
3. The SI unit for resistance (symbol: R) is the ohm
(symbol: Ω).
7.4 The Relationship Between Current, Voltage
and Resistance
1. Resistor is an electrical component that resists
the flow of electric current.
• the greater the boiling point, the more
soot is produced when the fractions are
burnt
• the greater the boiling point, the harder
the fractions burn
Product of
distillation
Uses
Petroleum gas Cooking gas
Petrol (gasoline) Fuel for vehicles
Naphta For making plastics
and polyvinyl chloride
(PVC)
Kerosene Fuel for aircraft
Diesel oil Fuel for lorries and
buses
Lubricating oil Lubricants for
machines
Fuel oil Fuel oil for ships
Bitumen To seal roads
3. Natural gas:
(a) consists of 90% methane, 10% of mixture of
ethane, propane, butane and pentane.
(b) It is usually found together with the
petroleum.
(c) It is used as fuel source and to produce
fertilisers.
4. Coal:
(a) Made up of carbon, oxygen, nitrogen and
sulphur.
(b) It is formed from plant remains that grew in
swamps.
Current
(a) Direction of electric current flow
Electron flow
(b) Direction of electron flow
Electron (negatively charged)
Proton (positively charged)
Neutron (no charged)
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2. Advantages of a series circuit:
(a) When more cells are added to the circuit,
the voltage and current increase. Hence, the
bulbs glow brighter.
(b) Bulbs light up with equal brightness because
the current flows through each bulb is the
same.
3. Disadvantages of a series circuit:
(a) If one of the bulbs is fused (burned out), the
other bulbs will not light up.
(b) The brightness of the bulbs decreases when
more bulbs are connected in series, because
the electrical energy is shared by more
bulbs.
7.7 Parallel Circuit
1. Current, voltage and total resistance in parallel
circuit:
2. Advantages of a parallel circuit:
(a) When one of the bulbs is burned out, the
other bulbs will still light up.
(b) Each electrical component can be controlled
by separate switches.
(c) All bulbs will light up with the same
brightness.
I = I1
+ I2
V = V1
= V2
1 1 1
— = — + —
R R1
R2
3. Disadvantage of a parallel circuit:
(a) When more bulbs are connected in parallel,
the dry cells will become weak quicker.
7.8 Magnetism
1. Magnetism is the properties and effects of
magnetic substances.
2. Ohm’s Law:
– the current flowing through a conductor is
directly proportional to its voltage.
Voltage (V)
Resistance (R) = —————–
Current (I)
– the greater the resistance, the smaller the
current.
– increasing the voltage supplied will increase
the current in the circuit.
7.5 Electric Circuits
1. An electric circuit is a path which allows an
electric current to flow through.
2. A simple electric circuit is made up of 3
components:
(a) A cell (a source of electrical energy)
(b) A bulb (a resistor)
(c) Connecting wire (a conductive path)
An electric circuit
3. Symbols of electrical components:
Electrical
component
Symbol
Electric cell
Battery (more
than one cell)
Switch
Bulb
Resistor
Dry cell
Wire
Light bulb
or
or
Electrical
component
Symbol
Rheostat
(Variable
resistor)
Fuse
Galvanometer
Voltmeter
Ammeter
4. Comparison between series and parallel
circuits:
Series circuit Parallel circuit
• Has only one path
for current to flow
through
• Light bulbs do not
glow as bright as
those connected in
parallel
• Has more than one
path for currect to
flow through
• Light bulbs glow
brighter than
those connected in
series
• If one light bulb
burns out, the
circuit becomes
incomplete. Hence,
other light bulbs
will not light up.
• If one light bulb
burns out, other
light bulbs will still
light up.
7.6 Series Circuit
1. Current, voltage and total resistance in series
circuit:
I = I1
= I2
= I3
V = V1
+ V2
+ V3
R = R1
+ R2
+ R3
V
V
V
V1
I1
R1
R2
I2
V2
V
I
V V V
V
V1 V2
V
I
I1R1 I2R2 I3R3
V3
G
V
A
or or
G
V
A
G
V
A
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(c) Gas turbine generator
(d) Diesel power plant
(e) Nuclear power plant
8.2 Transformers
1. A transformer is a device for changing the voltage
of an alternating current.
2. An alternating current (symbol: a.c.) flows back
and forth, reversing its direction.
2. Magnetic field is the area around a magnet where
a magnetic force can be detected.
3. The magnetic field of a magnet can be represented
by lines, called magnetic field lines.
4. The magnetic field lines have a certain pattern
and direction.
(a) The pattern of the magnetic field lines can
be shown by using iron filings.
(b) The direction of the magnetic field lines can
be detected by using a compass.
5. Characterstics of magnetic field lines:
(a) Run from the north pole to the south pole
of the magnet.
(b) Do not cross one another.
7.9 Electromagnetism
1. Electromagnetism refers to the properties and
effects of electromagnets produced by electric
current.
2. An electromagnet is a magnet that is produced
by the flow of electric current.
(a) Without electrical energy, an electromagnet
loses its megnetism.
(b) An electromagnet is a temporary magnet.
3. A straight line conductor carrying current produces
a concentric magnetic field lines around it.
Control
rods
Concrete wall
Steam
turbine
Condenser
Electrical
Output
Pump
PumpPump
Water
PumpPump
Water
Steam
generator
Reactor
38ºC27ºC
Steam
Diesel engine Generator
electric
current
Cardboard
Magnet
placed
under the
cardboard
Iron filings
Compass Magnetic
field lines
N
S
CHAPTER 8
Generation of Electricity
8.1 The Generation of Electrical Energy
1. Types of generators:
(a) Hydroelectric power plant
(b) Thermal generator
Copper wire
Card
Retort
stand
Power pack
Switch
Compass
Dam
Pylon
Tunnel Turbine and generator
Water
Boiler
Steam Pylon
Generator
CondenserBurner
Turbine
From water purification plant
Sea water
Water
Air
filter
Compressor
Combustion
chamber
Gas turbineSpark plug Generator
Electric tower
Exhaust
Motor
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3. Types of transformers:
(a) Step-up transformer
– To increase the output voltage.
– The secondary coil has more turns than
the primary coil.
(b) Step-down transformer
– To reduce the output voltage.
– The secondary coil has less turns than the
primary coil.
a.c.
input
voltage
a.c.
output
voltage
Soft iron core
Primary coil Secondary coil
a.c.
input
voltage
a.c.
output
voltage
Soft iron core
Primary coil Secondary coil
8.3 Electrical Power Transmission and Distribution System
Power
stations
Step-up
transformer
Switch
zone
National
Grid
Network
Main
substation
(Step-down
transformer)
Branch
substation 33 kV
Heavy
industrial area
11 kV 132 kV/
275 kV/
500 kV
132 kV/
275 kV/
500 kV
132 kV/
275 kV/
500 kV
Branch
substation 11 kV
Light
industrial area
Branch
substation 240 V
Residential
area
Branch
substation 415 V
Shopping
complexes
1. National Grid Network is a system of high voltage
circuits that connects the main power stations.
2. Advantages of National Grid Network:
(a) Ensures continuous and uninterrupted
electrical power supply to the consumers.
(b) Reduces the operational cost of electrical
energy transmission.
(c) Prevents wastage of electrical energy.
8.4 Electrical Power Supply and Wiring system in
Homes
1. Homes are supplied with 240 V alternating
current (a.c.).
Part Function
Mains
fuse
Breaks the circuit when current
exceeds a safe value
Mains
switch
Cuts off electrical power supply
from the mains when electricity
is not needed
Circuit
breaker
Cuts off the electric current that
flows under abnormal conditions
Live wire Carries the electric current from
the substation to the house
Neutral
wire
Carries the electric current from
the house back to the substation
Earth
wire
Connects an electrical appliance
to the earth or ground
Electric
meter
Measures the amount of
electricity used
2. Our home uses single-phase wiring system.
3. The commercial and industrial areas use three-
phase wiring system.
4. 3-pin plug:
Distribution systemTransmission systemGeneration Cable
Neutral wire
Earth wire
Cover removed Fuse
Cover
Live wire
11 kV
240 V/
415 V 33 kV 33 kV
33 kV 11 kV
Heavy
industrial
area
Transmission
system
Distribution
system
Light
industrial area
HospitalShopping
complex
Residential
area
132 kV/
275 kV/
500 kV
B
C
Transmission over
long distances
D
E E
A
A Components:
A – Power
station
B – Step-up
transformer
C – National
Grid
Network
D – Step-down
transformer
E – Branch
substation
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8.5 Cost of Electrical Energy Usage
Energy used (J)
1. Power (W) = ———————–
Time (s)
2. Power (P) = Voltage (V) × Current (I)
3. Energy (kWh) = Power (kW) × Time (h)
1 unit of electrical energy = 1 kWh
8.6 Fuse and Earth Wire
1. Fuse and earth wire are protection devices.
(a) Fuse breaks off the electrical circuit.
(b) Earth wire ensures the leakage of current
flows to the ground.
2. Function of the fuse:
(a) A fuse has a piece of short wire which has
a low melting point.
(b) When excess current flows through it, the
wire in the fuse melts and disconnects the
current.
3. Types of fuses:
(a) Replaceable wire fuse
(b) Cartridge fuse
4. Fuses have different ratings, according to the
maximum current they can carry. For example,
1 A, 2 A, 3 A, 5 A, 10 A and 13 A.
8.7 Safety Precautions in the Use of Electrical
Energy
1. Damaged appliances must be repaired by qualified
electrician only.
2. Avoid overloading a power point.
3. Avoid touching switches, wires or plugs with
wet hands, as this may cause electric shock or
electrocution.
4. Install Earth Leakage Circuit Breaker (ELCB) and
Miniature Circuit Breaker (MCB) in home wiring
system for additional protection against electrical
accidents.
8.8 Conserving Electrical Energy
1. We need to conserve electrical energy to prevent
wastage.
2. Ways to conserve energy:
(a) Use fluorescent lamps instead of incandescent
light bulbs.
(b) Use energy efficient electrical appliances.
(c) Use the washing machine with a full load.
(d) Switch off electrical appliances when they
are not in use.
CHAPTER 9
Stars and Galaxies
9.1 The Sun
1. The Sun is a star that is closest to the Earth.
2. Characteristics of the Sun:
(a) It is the centre of the solar system.
(b) It is the only star in the solar system.
(c) It is mainly made of hydrogen (70% to 80%)
and helium.
3. Structure of the Sun:
(a) Corona (outermost layer) is seen only during
a total solar eclipse.
(b) Chromosphere (middle layer) appears reddish
during a solar eclipse.
(c) Photosphere (innermost layer) is the Sun’s
surface as seen from the Earth. It has sunspots,
prominences and solar flares.
(d) Core (centre of the Sun) is the place where
nuclear fusion takes place, that is, hydrogen
is changed into helium, releasing a lot of
energy.
(e) Sunspots (dark patches) are cooler and they
can cause changes in the Earth’s climate, such
as extreme drought.
(f) Prominences are ‘giant flares’ which are huge
columns, extending thousands of kilometres
from the surface. It produces solar wind and
causes aurora.
(g) Solar flares are huge clouds of hydrogen that
explode violently on the Sun’s surface. They
Contact
Holder
Fuse wire
Contact
Metal
cap Fuse wire
Glass tube
Cartridge fuse
Replaceable wire fuse
3-pin plug
Live
wire
Neutral
wire
Earth
wire
Fuse
Carries
current
from the
substation
to the
house
Carries
current
from the
house
back
to the
substation
Carries
leakage
current
from the
appliances
to the
Earth
Prevents
excessive
current
flowing
into the
appliance
and
damaging it
• A 3-pin plug carries electric current from a
power station to an appliance in use, and
then returns it to the substation.
• A 3-pin plug also acts as a safety device to
protect an appliance in use from getting
damaged.
Corona
Chromosphere
Photosphere
Core
Prominence
Sunspots
Solar flare
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xv
also change the Earth’s climate and affect
the telecommunication systems on Earth.
9.2 Stars and Galaxies in the Universe
1. Stars:
(a) Made up of dust and gases (such as hydrogen
and helium).
(b) Generate heat and light through nuclear
fusion.
(c) Differ in size, brightness, colour and
temperature.
2. Arrangement of stars in ascending order of
temperature:
Red → Yellow → White → Whitish-blue → Blue
3. Arrangement of stars in ascending order of
size:
Neutron star → White dwarf star → Dwarf star
→ Giant star → Supergiant star
4. Formation of stars:
(a) Stars are formed from nebulae (singular:
nebula), which are made of clouds of dust
and gases.
(b) The nebula contracts when the gases and
dust exert a strong gravitational force on
each other.
(c) Further contraction causes the ball to become
denser until hydrogen atoms fuse to form
helium atoms – a nuclear fusion reaction.
(d) The reaction causes the temperature to rise
and causes the star to expand.
(e) The balance between the contraction and
expansion of star will form a stable star, such
as the Sun.
5. The death of stars:
(a) When nuclear fusion no longer takes place,
the size of the core of the star will reduce.
(b) The size of a star determines its lifespan.
(c) Massive stars have longer lifespan than
smaller ones.
(d) The death of a medium-sized star:
Red giant → White dwarf → Black dwarf
(e) The death of a large star:
Red giant → Supergiant → Supernova →
Neutron star
(f) The death of a super-large star:
Red giant → Supergiant → Supernova →
Black hole
6. Galaxies:
(a) Are collection of billions of stars, planets, dust
and gases held together by a gravitational
force
(b) Types of galaxies:
Types Description
Elliptical-shaped
galaxy
• It has a diameter between
3000 and 10 000 light years.
• It looks like a smooth,
round and oval-shaped disc,
and has no arms.
• It is the brightest at the
core and gradually fades
towards the edge.
• It is made up of old yellow
stars and does not contain
gas and dust, so new stars
are not formed.
• Example: M87 in the centre
of Virgo cluster.
Spiral-shaped
galaxy
• It has a diameter of about
20 000 to 100 000 light years.
• It is disc-shaped and made
up of stars gathering in
a whorl with spiral arms
at the edges. These arms
contain dust and gases.
• It has a bright centre. Its
centre has older stars. Its
arms have younger stars,
while dwarf stars and
nebulae. The arms rotate
around its centre.
• Example: The Milky Way,
Andromeda
Types Description
Irregular-shaped
galaxy
• It has a diameter between
25 000 and 32 000 light
years.
• It does not have a definite
pattern or shape.
• It exists in various different
forms and is usually made
up of young stars that are
very hot.
• Example: Large Magellanic
Cloud
7. The Milky Way:
(a) It is a spiral-shaped galaxy.
(b) The solar system is located in the Milky
Way.
8. The Universe:
(a) It consists of all the matter, energy and space
that exist.
(b) It has billions of galaxies, stars, planets and
particles.
(c) Its size is infinitive and unknown.
9.3 The Universe as a Gift from God
1. The Universe is a unique creation of God.
2. Everything that exists in the Universe is not
permanent: Stars are born and die out, new stars
are formed to replace them.
CHAPTER 10
Space Exploration
10.1 Developments in the Field of Astronomy and
Space Exploration
1. Astronomy is the study of objects in the
Universe.
2. The Greeks:
(a) The first people to study astronomy.
(b) First to declare that the Earth is spherical,
and the orbits of the planets are circular.
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xvi
3. The Islamic astronomers studied the rotation of
the Earth and the eclipses of the Sun and the
Moon.
4. Other developments:
(a) Hans Lippershey invested a telescope.
(b) Galileo Galilei was the first man to observe
objects in space with a telescope.
(c) Yuri Gagarin was the first person in space.
(d) Neil Armstrong was the first human to set
foot on the Moon.
(e) Aristotle believed wrongly that the Earth was
the centre of the Universe.
(f) Claudius Ptolemy supported Aristotle’s
belief that the Earth was the centre of the
Universe.
(g) Nicholas Copernicus (The father of the
modern astronomy) stated that the Sun is
the centre of the solar system.
5. Technology used in space exploration:
(a) Space telescope (such as Hubble Space
Telescope) – helps scientists to discover
distant objects
(b) Space probes – send images and data back
to Earth for analysis
(c) Space station – allows scientists to work in
space for a long period of time
(d) Space shuttles – carry astronauts to repair
and retrieve damaged satellites in space
(e) Satellites – unmanned devices which are
placed in the orbit of the Earth to carry out
certain functions.
Space telescope
Space probe
Space station
Space shuttle
Satellite
6. Types of satellites:
(a) Communication satellites – enable instant
radio and telephone communication, live
telecast and Internet applications
(b) Weather satellites – enable meteorologists to
predict weather hazards such as hurricanes
and floods
(c) Navigation satellites – guide ships and
aircraft
(d) Military satellites – improve national security,
defence and spying systems
(e) Environmental satellites – detect world’s
resources
7. Remote sensing is the means of using satellites
to study the conditions on Earth from space.
8. Remote sensing can be used in geology,
agriculture, forestry, disaster management and
national security management.
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