Download - Express Notes Science Form 3

All Rights Reserved ©2012 Ng Chee Kin

Written By Ng Chee Kin

B.Sc.(Hons.), MBA [email protected]

[email protected]

iii

EXPRESSEXPRESSEXpresS

CHAPTER 1Respiration

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 2Blood Circulation and Transport

2.1 Transport System in Humans

1. The human heart:

Oxygen

Lungs

HeartOther body cells

Movement of oxygenMovement of oxygenated bloodMovement of deoxygenated blood

HaemoglobinOxyhaemoglobin

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 37oC

Smoothmuscle

Endothelium

Lumen

Connective tissue

Connectivetissue

Smoothmuscle

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 3Excretion

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

EpidermisPhloemXylempith

vascular bundle

Root hairCortex

EndodermisXylemPhloem

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 dialysisor 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 4Reproduction

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

ScrotumTestis

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, takingalcohol 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 temperatureto 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 5Growth

5.1 Human Growth Pattern

1. Growth is an irreversible and permanent processin 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

AntherFilament

Stamen

Nectary

ReceptaclePedicel

Sepal

StigmaStyle

Pistil

OvaryOvule

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 65Age (years)

Hei

gh

t (c

m)

AdolescenceChildhood

Old ageAdulthood

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 6Land 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 GalenaIron

pyriteChina 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

MetalReaction 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 siliconand 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 7Electricity

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 generatorsand 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

R2I2

V2

VI

V V V

V

V1 V2

V

II1R1 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 voltageof 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 patternand 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

ElectricalOutput

Pump

PumpPump

Water

PumpPump

WaterSteam generator

Reactor

38ºC27ºC

Steam

Diesel engine Generator

electric current

CardboardMagnet placed under the cardboard

Iron filings

Compass Magnetic field lines

N

S

CHAPTER 8Generation 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

DamPylon

Tunnel Turbine and generator

Water

BoilerSteam Pylon

Generator

CondenserBurner

Turbine

From water purification plant

Sea waterWater

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. inputvoltage

a.c. outputvoltage

Soft iron core

Primary coil Secondary coil

a.c. inputvoltage

a.c. outputvoltage

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

Lightindustrial 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

Heavyindustrialarea

Tran

smis

sio

nsy

stem

Dis

trib

uti

on

syst

em

Light industrial area

HospitalShoppingcomplex

Residentialarea

132 kV/275 kV/500 kV

B

C

Transmission overlong distances

D

E E

A

A Components:A – Power stationB – Step-up transformerC – National Grid NetworkD – Step-down transformerE – 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 9Stars 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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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 spacethat 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 10Space 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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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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