expressnotes scienceform3

8/20/2019 Expressnotes Scienceform3

1/15

All Rights Reserved ©2012 Ng Chee Kin

Written By

Ng Chee KinB.Sc.(Hons.), MBA

[email protected]@blogspot.com.au


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EXPRESS EXPRESS

EXpresS �

�

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 BronchusTrachea Nose

1.2 Transport of Oxygen in the Human Body

1. The oxygen dissolves in the moist lining of thealveolus and then it diffuses into the blood

capillaries.

2. In the blood capillaries, oxygen will combinewith 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 andhydrocarbons from vehicles and factories.

2. Tar and asbestos dust are carcinogenic, whichmeans they can cause lung cancer if inhaled

excessively.

3. Bacteria, viruses and other microorganismsproduce toxins which cause illnesses.

4. We need to improve the quality of air in orderto preserve healthy respiratory system.

CHAPTER 2

Blood Circulation and Transport

2.1 Transport System in Humans

1. The human heart:

Oxygen

Lungs

Heart

Otherbodycells

Movement of oxygenMovement of oxygenated bloodMovement of deoxygenated blood

HaemoglobinOxyhaemoglobin

Key:

Oxygenated blood returnsto the heart

Oxygen enters blood inthe lungs

Deoxygenated bloodpumped out of the heart

Oxygenated bloodpumped out of theheart

Deoxygenated bloodreturns 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

Semilunarvalves

Rightatrium

Tricuspidvalve

Rightventricle

Aorta

Pulmonary artery

Left atrium

Bicuspidvalve

Leftventricle

Pulmonaryvein

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Deoxygenated blood Oxygenated blood

AortaPulmonary artery

Vena cava

Right atrium

Vena cava

Tricuspidvalve

Rightventricle

Cardiac muscle

Pulmonaryvein

Semilunarvalves

Left atrium

Bicuspidvalve

Septum

Left ventricle

2. Functions of the heart:(a) Pumps blood to all parts of the body.

(b) Transports nutrients and oxygen to the bodycells.

(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 andpulmonary artery

Yes No

5. Double circulatory system:

(a) Deoxygenated blood is pumped from theheart to the lungs and oxygenated blood

flows back again to the heart.

(b) Oxygenated blood is pumped from the heatto the rest of the body and deoxygenated

blood flows back again to the heart.

6. Human blood transports many substances in ourbody.

Substance

transportedFrom To

Oxygen (in

the form ofoxyhaemoglobin)

Lungs All body

cells

Carbon dioxide All body cells Lungs

Digested food

(glucose, aminoacids)

Small

intestine

Liver and

all bodycells

Waste materials(such as urea)

Liver andcells

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 bloodcells

Defends the body againstdiseases

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

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 (forexample, head, arms,

legs)

Left

ventricle

Left

atrium

Oxygenated

blood

Lung

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4. Compatibility of blood groups:

Recipient’s blood

Donor’s groupblood 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 vascularbundle.

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, thegreater 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 wasteproducts 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 watercontent, 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

PhloemXylem

pith

vascularbundle

Root hairCortex

EndodermisXylem

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 andwater 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 functionsproperly.

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 thecell wall and stomata.

3. Mineral salts such as calcium carbonate and

calcium oxalate are retained in the plant ascrystals.

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 usefulto 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

ScrotumTestis

Seminalvesicle

Prostategland

Seminal vesicle

Prostate gland

Epididymis

Penis

Testis Scrotum

Urethra

Vas deferens

4.2 Male Reproductive System

Organ Function

Testis ( plural :testes)

• Produces sperms (the malegametes)

• Produces male sex hormones

Scrotum • Holds and protects the testes

Sperm duct(vas deferens)

• Transports sperms from thetestes to the urethra inside

the body

Urethra • Allows sperms to flow out of

the body

Penis • Transfers semen into vagina

during copulation

Seminalvesicles

• Secrete fluid which containsnutrients 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 physiologicalchanges 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 grainand 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 anucleus 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 walland 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 femalegametes)

• Produces female sex hormones

Fallopiantube (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 nutritiousfood and have a balanced diet.

2. Pregnant women should avoid smoking, taking

alcohol or drugs.

4.7 Importance of Research in HumanReproduction

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 producingnew plants from any vegetative parts of theparent 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 techniquesused 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 bymeasuring 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

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 fromthe 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 aseed and the ovary become the fruit.

4.11 Germination of Seeds

1. A seed is made up of an embryo and a foodstore wrapped in a testa (seed coat).

Infancy

Slowgrowth Rapid

growth

Rapidgrowth

Minimalgrowth Negative

growth

0 3 13 20 65 Age (years)

H e i g h 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

Pist il 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 GalenaIron

pyriteChinaclay

Calciumsilicate

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

waterAction of

heat

• Most metal oxides are stable

• Metal sulphides break downinto metal oxide and release

sulphur dioxide gas

6.2 Reactions Between Metals and Non-metals

1. Metals react with non-metals at different ratesto form stable compounds:

(a) Metals react with oxygen to form metaloxide

(b) Metals react with sulphur to form metal

sulphide

Metal

Reaction

rate withoxygen

Reaction

rate withsulphur

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, waterand carbon dioxide

(c) Breaks down into calcium oxide and carbondioxide 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 formedwhen slaked lime is added with more water.

6.5 Natural Fuel Resources and Their Importance

1. Fossil fuels include petroleum, natural gas andcoal.

2. Petroleum:

(a) Formed from organism remains buried insediment 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 moreviscous 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 becausethey are neutral.

6. An atom becomes positively charged when itloses 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 thenegative 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 otherelectrical components in a circuit.

– the deflection of the pointer of the ammeter

shows the value of current flowing throughthe components.

– the SI unit for electric current is ampere

(symbol: A). 2. Measuring voltage (symbol: V ):

– connect a voltmeter in parallel to otherelectrical components in a circuit.

– the deflection of the pointer of the voltmetershows the value of voltage across thecomponents.

– 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, Voltageand 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 areburnt

• the greater the boiling point, the harder

the fractions burn

Product of

distillationUses

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 thepetroleum.

(c) It is used as fuel source and to producefertilisers.

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 becausethe 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 morebulbs.

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, theother 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 = I 1 + I

2

V = V 1 = V

2

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 ofmagnetic substances.

2. Ohm’s Law:

– the current flowing through a conductor isdirectly 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 3components:

(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:

Electricalcomponent

Symbol

Electric cell

Battery (morethan one cell)

Switch

Bulb

Resistor

Dry cell

Wire

Light bulb

or

or

Electrical

componentSymbol

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 asthose connected in

parallel

• Has more than one

path for currect to

flow through• Light bulbs glow

brighter thanthose connected in

series

• If one light bulbburns out, the

circuit becomes

incomplete. Hence,other light bulbs

will not light up.

• If one light bulbburns out, other

light bulbs will still

light up.

7.6 Series Circuit

1. Current, voltage and total resistance in seriescircuit:

I = I 1 = I

2 = I

3

V = V 1 + V

2 + V

3

R = R1 + R

2 + R

3

V

V

V

V 1

I 1

R1

R2I 2

V 2

V

I

V V V

V

V 1 V 2

V

I I 1R1 I 2R2 I 3R3

V 3

G

or or

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 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 poleof 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 electromagnetloses its megnetism.

(b) An electromagnet is a temporary magnet.

3. A straight line conductor carrying current producesa concentric magnetic field lines around it.

Controlrods

Concrete wall

Steamturbine

Condenser

ElectricalOutput

Pump

PumpPump

Water

PumpPump

Water

Steam

generator

Reactor

38ºC27ºC

Steam

Diesel engine Generator

electriccurrent

CardboardMagnet

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

Retortstand

Power pack

Switch

Compass

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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

Powerstations

Step-up

transformerSwitchzone

National

GridNetwork

Mainsubstation

(Step-down

transformer)

Branch

substation33 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

Branchsubstation 240 V

Residentialarea

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 inHomes

1. Homes are supplied with 240 V alternatingcurrent (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 neededCircuit

breaker

Cuts off the electric current that

flows under abnormal conditions

Live wire Carries the electric current fromthe substation to the house

Neutralwire

Carries the electric current fromthe house back to the substation

Earth

wire

Connects an electrical appliance

to the earth or ground

Electricmeter

Measures the amount ofelectricity 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

T r a n s m i s s i o n

s y s t e m

D i s t r i b u t i o n

s y s t e m

Lightindustrial 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 ElectricalEnergy

1. Damaged appliances must be repaired by qualifiedelectrician 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 electricalaccidents.

8.8 Conserving Electrical Energy

1. We need to conserve electrical energy to preventwastage.

2. Ways to conserve energy:

(a) Use fluorescent lamps instead of incandescentlight 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’ssurface 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 ofenergy.

(e) Sunspots (dark patches) are cooler and they

can cause changes in the Earth’s climate, suchas extreme drought.

(f) Prominences are ‘giant flares’ which are huge

columns, extending thousands of kilometresfrom 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

Metalcap Fuse wire

Glass tube

Cartridge fuse

Replaceable wire fuse

3-pin plug

Live

wire

Neutral

wire

Earth

wireFuse

Carriescurrentfrom the

substation

to thehouse

Carriescurrentfrom the

house

backto the

substation

Carriesleakagecurrent

from the

appliancesto the

Earth

Preventsexcessivecurrent

flowing

into theappliance

and

damaging it

• A 3-pin plug carries electric current from apower station to an appliance in use, and

then returns it to the substation.

• A 3-pin plug also acts as a safety device toprotect 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 nuclearfusion.

(c) Differ in size, brightness, colour and

temperature.

2. Arrangement of stars in ascending order oftemperature:

Red→ Yellow→ White→ Whitish-blue→ Blue

3. Arrangement of stars in ascending order ofsize:

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 dustand gases.

(b) The nebula contracts when the gases and

dust exert a strong gravitational force oneach other.

(c) Further contraction causes the ball to become

denser until hydrogen atoms fuse to formhelium atoms – a nuclear fusion reaction.

(d) The reaction causes the temperature to riseand causes the star to expand.

(e) The balance between the contraction andexpansion of star will form a stable star, suchas 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 thansmaller 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, dustand gases held together by a gravitational

force

(b) Types of galaxies:

Types Description

Elliptical-shapedgalaxy

• It has a diameter between3000 and 10 000 light years.

• It looks like a smooth,

round and oval-shaped disc,and has no arms.

• It is the brightest at thecore and gradually fadestowards the edge.

• It is made up of old yellow

stars and does not containgas and dust, so new stars

are not formed.• Example: M87 in the centre

of Virgo cluster.

Spiral-shapedgalaxy

• It has a diameter of about20 000 to 100 000 light years.

• It is disc-shaped and made

up of stars gathering ina whorl with spiral arms

at the edges. These arms

contain dust and gases.• It has a bright centre. Its

centre has older stars. Itsarms have younger stars,

while dwarf stars and

nebulae. The arms rotatearound its centre.

• Example: The Milky Way,

Andromeda

Types Description

Irregular-shapedgalaxy

• It has a diameter between25 000 and 32 000 light

years.

• It does not have a definitepattern or shape.

• It exists in various different

forms and is usually madeup 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 MilkyWay.

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 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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3. The Islamic astronomers studied the rotation of

the Earth and the eclipses of the Sun and theMoon.

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 setfoot on the Moon.

(e) Aristotle believed wrongly that the Earth was

the centre of the Universe.

(f) Claudius Ptolemy supported Aristotle’sbelief that the Earth was the centre of the

Universe.

(g) Nicholas Copernicus (The father of themodern 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 discoverdistant 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 repairand retrieve damaged satellites in space

(e) Satellites – unmanned devices which are

placed in the orbit of the Earth to carry outcertain functions.

Space telescope

Space probe

Space station

Space shuttle

Satellite

6. Types of satellites:(a) Communication satellites – enable instant

radio and telephone communication, livetelecast and Internet applications(b) Weather satellites – enable meteorologists to

predict weather hazards such as hurricanesand floods

(c) Navigation satellites – guide ships and

aircraft(d) Military satellites – improve national security,

defence and spying systems

(e) Environmental satellites – detect world’sresources

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 andnational security management.

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