Form 3 (PMR)


Chapter 1 : Respiration

1.      The human respiratory system consists of the nasal cavity, trachea, bronchi, lungs, rib cage, diaphragm and the intercostals muscle.
2.      The structure of the human lungs consists of the bronchus, bronchioles and alveoli.
3.      The bronchus is a branch of the trachea.
4.      Bronchioles are small tubes that branches off the bronchi.
5.      The alveoli are air sacs found at the end of each bronchiole.
6.      Breating involves inhalation and exhalation.
7.      During inhalation,
©      The rib cage moves upwards and outwards
©      The diaphragm contracts and moves downwards
©      The volume of the thoracic cavity increase
©      The air pressure in the thoracic cavity becomes lower than the air pressure outside the body
8.      During exhalation,
©      The rib cage moves downwards and inwards
©      The diaphragm relaxed and moves upwards
©      The volume of the thoracic cavity decreases
©      The air pressure in the thoracic cavity becomes higher than the air pressure outside the body
9.      The diffusion of oxygen from the alveoli into the blood capillaries takes place efficiently because
РThe wall of the alveolus and the wall of the blood capillaries are only one cell thick
РThe alveoli are surrounded with a large number of blood capillaries
РThe alveoli have a large surface area
РThe walls of the alveoli are always moist
10.   Oxygen is transported by the red blood cells in the form of oxyhaemoglobin.
11.   Substances that are harmful to our respiratory system are
Ë Nicotine
Ë Tar
Ë Sulphur dioxide
Ë Carbon monoxide
Ë Haze
12.   Example of disease that affect the respiratory system are
Q  Bronchitis
Q  Asthma
Q  Emphysema
Q  Pneumonia
Q  Influenza
Q  Tuberculosis
Q  Lung cancer
13.   We must practice good habits to improve the quality of that we breathe in.
Chapter 2 : Blood circulation and transport

  1. The human blood circulatory system consists of the heart, arteries, veins andcapillaries.
  2. The blood circulatory system is a system of tubes that ensure one-way flow of blood with a pump and valves.
  3. Heart pumps blood to the lungs and to all parts of the body.
  4. The human heart is divided intofour chambers
§      Right atrium
§      Left artium
§      Right ventricle
§      Left ventricle
  1. Oxygenated blood
ª      Has a high concentration
ª      Has a low concentration
ª      Is bright red
ª      Flows in the arteries
  1. Deoxygenated blood
v  Has a low concentration of oxygen
v  Has a high concentration of carbon dioxide
v  Is dark red
v  Flows in the veins
  1. The system of blood circulation where blood passes through the heart twice is called thedouble circulatory system.
  2. Blood transpots nutrients and oxygens to cells and carries carbon dioxide andwaste products away from the cells.
  3. Blood consists of
·         Red blood cells
·         White blood cells
·         Platelets
  1. Blood in humans is classified into four groups, namely A, B, AB, and O.
  2. Blood transfusion is the transfer of blood from a donor to a recipient.
  3. People with blood group O can donate blood to recipients of all blood groups. They are called universal donors.
  4. People with blood group AB can receive blood from donor of all blood groups. They are called universal recipients.
  5. Blood donation is important because blood has no substitute and cannot be manufactured synthetically.
  6. Wilting occurs when plants lose more water than they receive.
  7. Plants lose water through stomata by a process called transpiration.
  8. A stomata consists of an opening enclosed by two kidney-shape guard cells.
  9. The factors affecting the rate of transpiration are
Ë Light
Ë Temperature
Ë Humidity
Ë Wind
  1. The roles of transpiration is
©      To cool the leaves
©      In the transport of water and minerals
  1. Xylem transports water and minerals from the roots to the leaves.
  2. Phloem transports glucose from the leaves to the roots and other parts of the plant

Chapter  3 : Excretion
  1. Excretion is a process in which excretory organs remove waste products from the body.
  2. The excretory organs in humans are the skin, lungs and kidneys.
  3. Skin removed water, mineral salts and a small amount of urea.
  4. Lungs removed water and carbon dioxide.
  5. Kidneys removed water, mineral salts and urea.
  6. Excretion helps to:
-          Maintain our body’s salt content
-          Control our body temperature
-          Control the pH or acidity of our blood
  1. The urinary system consists of the kidneys, ureters, urinary bladder and urethra.
  2. The human kidney is shaped like a bean and consists of the cortex, medulla and pelvis.
  3. The functions of the kidneys is to
-          Remove urea, excess mineral salts and water in the form of urine.
-          Regulate and maintain the balance of the body water content by controlling the amount of urine produced
-          Maintain the blood pressure at a normal level by regulating mineral salts levels in the blood
  1. Kidney failure is a condition in which the kidneys cannot function normally.
  2. A person with kidney failure can be helped by using a dialysis machine.
  3. The waste products of plants are carbon dioxide, water, oxygen, mineral salts and nitrogenous wastes.

Chapter 4 : Reproduction
  1.  Reproduction is the creation of offspring from existing adults.
  2.  There are two types of reproduction:
-          Sexual reproduction – involves gametes or reproductive cells
-          Asexual reproduction – no gamete are involves
  1. Fertilization is the fusion of a sperm and an ovum.
  2. Fertilization that takes place inside the body of the female individual is called internal fertilization
  3. Fertilization that takes place outside the body of the female individual is called external fertilization.
  4. Asexual reproduction occurs in various ways:
-          Binary fission
-          Budding
-          Spore formation
-          Vegetative reproduction
-          Regeneration
  1. The human male sexual organs consists of the testes.
  2. A sperm cell consists of a head, neck, middle piece and tail.
  3. Male puberty usually occurs between the ages of 12 and 14.
  4. The female sexual organs consists of the ovaries and the uterus.
  5. Female puberty usually occurs between the ages of 10 and 12.
  6. Physical, physiological and emotional changes occurs in males and females at puberty.
  7. Menstruation is the discharge through the vagina which consists of blood, mucus, the cells of the uterus lining and the unfertilized ovum.
  8. Menstruation usually occurs once in every 28 days and usually last for  3 – 5 days
  9. Ovulation is the release of an ovum by the ovary and usually occurs on the 14 day in the menstrual cycle
  10. The fertile phase of the menstrual cycle is from the 11 day to the 17 day
  11. Implantation is a process in which the embryo attaches itself on the wall of the uterus
  12. The embryo continues to develop in the uterus after implantation
  13. harmful substances such as drugs , alcohol and chemical in tabaco smoke may cause miscarriages and birth defects such as mental retardation and brain damage in the foetus 
  14. sterility is the inability to reproduce 
  •  
Chapter 5 : Growth

THE PATERN OF HUMAN GROWTH

1. Growth is a process that take place in all living things. 
2. The process of growth involves 
                 i. increase in size of organism. 
                 ii. change in appearance of organism. 
                 iii. increase in number of cells. 
                 iv. development of organs function of organism. 
 Human growth
1. Growth in human beings can be measured in two ways namely by: 
                i. body weight 
                ii. body height 
2. The growth process in human can be divided into several stages. At each stages, form, size and appearance of man change. 
3. Generally, there are five stages of live in human: 
                i. infancy 
                ii. childhood 
                iii. adolescence 
                iv. adulthood 
                v. old age 
4. The five stages of live in human can be displayed by the growth curve.
5. growth in human is divided into the following stages. 
               i. Infancy   
          - infancy is from 0-1 year. The rate of growth is rapid. 
              ii. Childhood 
          - childhood is from 1-12 years. The rate of growth is slower until adolescence. 
              iii. adolescence  
         - Adolescence is from 12-20 years. The rate of growth increase slightly. 
              iv. adulthood 
         - the rate of growth is constant or zero. This means that growth in human has stopped.                           Nevertheless, parts which grow throughout life are skin, nail and hair. 
              v. old age 
        - The rate is negative and the size of the human body reduces. This stages ends in death. 
6. Although the growth curve of human beings is generally sigmoid, but there is difference in the growth in men and women
7.  growth curves of men and woman.
            i. the growth rate of a boy is the same as that of the girl during infancy. 
           ii. However, the growth of boy exceeds that of a girl during childhood. 
           iii. Between the ages 12-14, the growth rate of a boy exceeds that a girl. This is because a girl achieves puberty at earlier age (about 12 years old) and ends her adolescence earlier (about 16 years old). A boy reaches puberty at a later age (about 14 years old) and end his adolescence at about 18 years old. So, the height of a girl exceeds that of a boy at this early adolescence stage.
8.. The effects on nutrition on the growth of children.  
         - Childhood is most important stage in the growth of man. So, children must be given: 
a) a balanced diet because nutrients such as carbohydrates,  proteins, fats, vitamins and mineral salts ensure a healthy growth  and prevent various deficiency diseases such as marasmus, rickets, kwashiorkor and beri-beri. 
b) Guidance, protection, love and education to ensure total spiritual 
growth.

CHAPTER 6: LAND AND ITS RESOURCES 
6.1 The Various Minerals Found in the Earth’s Crust.
1..     Mineral is natural element or compound found in the Earth’s crust.  
2. A mineral has a composition and a specific crystalline structure. Examples of minerals are calcite, feldspar, quartz, mica, marble and silicate. 
3.. Only inactive elements can exist freely in the Earth’s crust. Meanwhile, active elements will react with other elements to form particular compounds. 
4.. Natural elements commonly found in the Earth’s crust are gold, silver, platinum, mercury and arsenic. 
5.. Table below shows the percentage of elements in minerals found in the Earth’s crust. 
elements % by weight
  • oxygen (46.6)
  • silicon (27.7)
  • aluminium (8.1)
  • iron/ferrum (5.0)
  • calcium (3.6)
  • sodium (2.8)
  • potassium (2.6)
  • magnesium (2.1)
  • titanium (0.4)
  • hydrogen/carbon (0.14)
6. Almost 75% of the weight of a mineral in the Earth’s Crust is made up of oxygen and silicon elements. Thus, silicate minerals which contain oxygen and silicon elements make up the largest amount. Examples of silicate minerals include quartz, feldspar, mica and clay. 

7. Minerals that do not contain silicon element are known  as non-silicate minerals. Examples of  non silicate minerals are  calcite, dolomite, magnetite and hematite. 

8. Other non metallic elements such as oxygen, sulphur and carbon usually exist in the form of compounds such as oxides, sulphides and carbonates. 

9. Less active elements combine with oxygen and sulphur  to  form oxides and sulphides such as iron oxide, aluminium oxide, lead sulphide and iron sulphide. 
  • Element in Natural Compounds 
  • Types of compounds Elements present
  • Oxides metal and oxygen
  • Carbonates metal, carbon and oxygen
  • Sulphides metal and sulphur
  • Silicates metal, silicon and oxygen
  • Silica silicon and oxygen
10. Sulphides react with oxygen to form sulphates. On the other hand, oxides will convert into carbonates when reacting with water and carbon dioxide. 

11.Table below shows a few examples of minerals compounds found in the Earth’s Crust. Types of minerals, Examples Of Natural Minerals Chemical name (Mineral Content) 
  • bauxite aluminium oxide 
  • Aluminium and oxygen 
  • hematite iron oxide iron and oxygen
  • magnetite magnesium oxide 
  • Magnesium andoxygen 
  • cassitetite tin oxide tin and oxygen sulphide 
  • galena lead sulphide lead and sulphur
  • pyrite iron sulphide iron and sulphur
  • chalcocite copper sulphide copper and sulphur
  • blende zinc sulphide zinc and sulphur carbonate 
  • calcite (marble) calcium carbonate calcium, carbon and oxygen 
  • magnesite magnesium carbonate 
  • Magnesium, carbon and oxygen 
  • dolomite magnesium carbonate 
  • Magnesium, carbon and oxygen  
  • malachite copper carbonate copper, carbon and oxygen 
  • Lime stone  calcium carbonate  calcium, carbon, oxygen 
  • Clay aluminium silicate aluminium, silicon, oxygen 
  • Mica potassium aluminium silicate potassium, aluminium, silicon, oxygen 
  • lime water
  • Calcium chloride  calcium chloride oxygen
12. Different minerals have different characteristics. Minerals posses different characteristic in terms of: 
                  i. hardness 
                 ii. solubility in water 
                 iii. reaction to heat and its effects

Hardness of Minerals
1. Hardness of mineral refers to the resistance offered by the mineral on being scratched. The hardness of a mineral is measured in Moths unit. 

2. Most minerals are hard. These minerals can only be scratched by hard objects such as knives. Nevertheless, hard minerals can scratch softer minerals. 

3. All minerals made up of carbonate, oxide and sulphide compounds are hard. 

4. Diamond is the hardest mineral while talc is the softest mineral. 

Solubility of Minerals in Water
1. All minerals of metal oxides, sulphides and carbonates are insoluble in water, except minerals of metallic potassium and sodium compounds.

2. The following experiment shows the solubility of various mineral in water. Conclusion: metals such as potassium and sodium are very active their compounds are soluble in water. 

The Effect of Heat on Some Metal Carbonates, Oxides and Sulphides.
                   i. Action of Heat on Metal Carbonates
1. All metal carbonates decompose when heated,  except  potassium carbonate and sodium carbonate because both the metal carbonates are very stable. 
2. The heating of metal carbonates form metal oxides and carbon dioxide gas. 

   6.2.1 Metals

1. Metals are elements that have the following properties: 
                       a. have shiny surfaces and can be polished. 
                       b. Metal are good conductors of electricity. 
                       c. Metal are elastic, that is can be beaten into specific shapes. 
                       d. Metal have very high melting points. 
2. Examples of metals are  magnesium, aluminium, zinc, iron, silver, mercury, copper, lead and platinum.

6.2.2 Non-Metals

1. Non metal are elements that have the following properties: 
                     a. have dull surfaces (do not shine) 
                     b. non metals are poor heat conductors 
                     c. non metals are poor electrical conductors 
                     d. non metals have low densities  
                     e. non metal are brittle, easily broken up when beaten 
                      f. non metal have low melting points. 

2. Examples of non metals are  oxygen, carbon, sulphur, bromine, iodine, chlorine and hydrogen. 

CHAPTER 7: ELECTRICITY 

1. ELECTROSTATICS 
A. Static Electrical charges 

              i. All matters are made of small particles called atoms. 
              ii. Structure of an atom; 
              iii. Atoms contains particles; proton, neutrons and electrons. Protons and neutrons form the    nucleus of atoms and electrons move around the nucleus. 
             iv. Proton and electron have a property called electric charge, and neutrons have no electric charge. 
             v. Protons have positive electric charged and electrons have negative electric 
charged. 
            vi. An atom contains equal amount of proton and electrons, so the positive and negative charges cancel out. Therefore, an atom has no net electric charge. 
           vii. An object is charged when there is a transfer of electrons. 

                   a. an object is neutral if its atoms have the same amount of protons and 
electron. 
                   b. An object is positively charged if the amount of protons more than the 
amount of electrons in its atoms. 
                  c. An object is negatively charged if the amount of electrons more than 
the amount of protons in its atoms. 
         viii. The transfer of electrons causes two types of electrical phenomena. 
               a. static electricity – phenomena where charges that are not moving. PMR 09 
              b. Current electricity – phenomena where the charges are moving. 
         ix. Electrostatics is the study of static electric charges or electric charges at rest (not moving). 

B. Producing static electrical charges 

                     i. Two dissimilar objects can be charged through friction. 
                    ii. Two neutral objects will be charged when they are rubbed together. 

            a. example; 
            b. a plastic ruler is rubbed with a handkerchief and brought near a stream of water. The ruler pulls the stream closer. 
            c. A balloon is rubbed with a silk cloth and brought near a piece of paper. 

The balloon attracts the paper. 
                 iii. Objects can lose or gain electrons by rubbing with  different types of 
objects. 
                iv. Matter carries out two types of charges, that is positive charge and the negative charge. 
               v. An object is said to be neutral if it has the same  number of positive charges and negative charges. 
              vi. The negative charges are electrons which are free to move from one object to another. 
              vii. If a neutral object loses electrons, it becomes positively charged. 
              viii. If a neutral object gains electrons, it becomes negatively charged.

C. properties of static electrical charges 

             i. same charges repel each other. 
             ii. Opposite charges attract each other.

Detecting static electrical charges

            iii. Electroscope is a device that is used to detect and identify the presence of static electric charges on the device itself or upon other nearby objects. 
            iv. The most commonly used electroscope in a laboratory is the gold leaf electroscope. 
             v. Structure of a gold leaf electroscope
             vi. Using an electroscope to identify static electric charges in an object: 

                          a. The presence of charge in an object can be determined by observing 
any deflection on the gold leaves. 
                          b. When the electroscope is cot charged, the gold leaves hang straight down. When the electroscope is charged, the gold leaves deflect from 
its normal. 
                    ii. Everyday phenomena caused by static electrical charges. 
                     
2. SAFETY MEASURE 

 1. A strip is used to prevent static charges from accumulating on the tanker. 
2. A lightning conductor is used to protect a building from being damaged by lightning. 

3. ELECTRICITY 
A. Electricity 

             i. Electricity is a form of energy produced by electric current. 
             ii. Electricity is used in many ways, such as lightning up a bulb, heating a kettle or spinning a ceiling fan. 
            iii. Electricity can be obtained from various sources

B. current and voltage 
            i. current is the rate of flow of charges (or electrons) through a conducting medium such as metal. Current increases when more electrons are flowing through a conductor. 

          ii. The flowing of electrons through a conductor is driven by voltages, 
produced by batteries or generators. 

         iii. Voltage is the difference in potential energy that causes electrons to flow from an area with more electrons to an area with fewer, producing an electric current. 

         iv. Van de Graff generator is a device that produces a  high voltage by collecting static electrical charges. 


4. MEASURING ELECTRICITY 
1. Electric current is measured by using an ammeter. 
2. Ammeter is connected in an electrical circuit in series.
3. Voltage is measured by using a Voltmeter. 
4. Voltmeter is connected in an electrical circuit in parallel. 
5. The symbol of current is I and its SI unit is the ampere (A). 
6. The symbol of voltage is V and its SI unit is the Volt (V). 
7. The symbol of resistance is R and its SI unit is the Ohm (Ω ).

5. THE RELATIONSHIP BETWEEN CURRENT, VOLTAGE AND RESISTANCE. 
1. The higher the resistance, the smaller the current  that flows through the circuit. 
2. The higher the voltage, the bigger the current that flows through the circuit.
3. Voltage is directly proportional to the current. 
V α I   or  R = 
I
V
   
The symbols, V, I and R represent the following: 
   V = voltage (V) 
   I = Current (A) 
   R = resistance (Ω ) 

6. THE PARALLEL AND THE SERIES CIRCUITS 
6.1 Components of an Electric Circuit and Symbols 
1. A simple circuit consists of a source of electrical energy, connecting wires and other electrical component. 
2. The components of an electrical circuit can be represented by symbols.

6.2 Circuit Diagram 
1. Closed circuit - electric current can flow from one end of dry cell to the other and the bulb will light up. 
2. Open Circuit  - Electric current cannot flow in the circuit and the bulb will not light up.

6.3 Series Circuit and Parallel Circuit 
1. A series circuit is a complete circuit that has only one path for current flow. 
2. Each component in a series circuit is connected to the next to form a single path. 
3. A parallel circuit is a complete circuit that has two or more paths for current flow

7. CURRENT, VOLTAGE AND RESISTANCE IN A SERIES CIRCUIT
1. The current that flows through each bulb in a series circuit is the same. 
2. The voltage supplied by the electrical source is shared by the all bulbs. The voltage across the circuit is the same as the sum of the voltage across each bulb. 
3. The total resistance in a series circuit is the sum of the resistance in each bulb. 

8. CURRENT, VOLTAGE AND RESISTANCE IN A PARALLEL CIRCUIT.
1. The current supplied by the electrical source in a parallel circuit is the same as the sum of the current that flows through each branch of the circuit. 
2. The voltage across each bulb is the same as the voltage supplied by the electrical source. 
3. The total resistance in the circuit is represented by the following formula. 

9. MAGNETISM 
1. A magnetic field is the area around a magnet where  magnetic effects or magnetic forces can be felt.
2. Magnetic fields are represented by the magnetic lines of forces. 
3. The direction of the magnetic field can be seen by plotting using a compass. 
4. The magnetic field or the lines that represent magnetic force do not meet each other and are closest together near the poles. 
5. The lines of magnetic force begin from the north pole and end at the south pole. 
6. This is because the magnetic field is the strongest near the poles. Away from 
the poles, the lines are further apart as the field is weaker. 
7. The direction of the magnetic field can be detected by using a compass. 

10. ELECTROMAGNETISM. 
1. A current flowing through a straight conductor produces a magnetic field around the conductor. 
2. The magnetic field produced around a straight conductor is circular in shape
3. An electromagnet is a conductor that has the same properties as a magnet. 
4. When current flows around a piece of iron, the iron becomes a magnet. However, its magnetism disappears when the current stops flowing. 
5. The strength of the magnetic field of an electromagnet can be increased by. 
                     a. Increasing the number of coils in a solenoid. Solenoid is an electrical conductor wound into a cylindrical coil. When current flows through a solenoid, the magnetic field pattern formed resembles the magnetic field pattern of a permanent bar magnet. 
                    b. Increasing the current that flows through the solenoid. 
                    c. Reducing the diameter of a solenoid. 
                    d. Iron core – magnetic field is stronger if a soft iron core (pure iron) is placed inside the solenoid.
 6. The poles of solenoid can be identified in the following ways: 
                   a. The pattern of the current can be seen from the ends. When a solenoid is viewed from its end, the pattern of current seen represents the pole of the end. b. Left hand grip rule: When the hand is held as shown in figure below, the direction of the thumb represents the direction of  the north pole while the direction of the other fingers represents the direction of the current. 

CHAPTER 8: GENERATION OF ELECTRICITY 
8.1 GENERATION OF ELECTRICAL ENERGY
1. Electrical energy for home and commercial use is produced by machines called generators. 

2. Generators convert mechanical energy to electrical energy

3. Turbines are usually connected to the copper coil of the generator by a shaft. 

4. When the turbines are turned, the spinning shaft will cause the copper coil to spin and electrical energy is produced. 

5. There are various type of generator:
                       a. Thermal generator 
                       b. hydroelectric generator 
                       c. nuclear generator 
                       d. gas turbine generator 
                       e. diesel generator

7. In a thermal power station, fossil fuels such as petroleum, coal and natural gas are used to heat water in a boiler to produce steam under high pressure. 

8. The steam is used to turn the turbines of a thermal generator.

9. In a hydroelectric power station, water flowing at  high speed and pressure form the dam forces the turbines to rotate the generator to produce electrical energy. 

10. In a nuclear power station, radioactive substances  such as uranium and plutonium are used to produce heat by nuclear reactions in a reactor. The heat is used to heat water to produce steam. The steam is then used to turn the turbines of a nuclear generator. 

11. In a gas turbine power station, natural gas or petroleum is burned in a highpressure combustion chamber. The hot gases produced are used to turn the turbines of a gas turbine generator. 

12. In a diesel power station, a diesel motor is used to turn the copper coil of a diesel generator. Diesel generators are usually used to produce small supplies of electrical energy to small villages. 

Alternative Sources of Energy 
1. Except for hydroelectric power stations, other types of power stations use nonrenewable sources of energy. 

2. Two alternative sources of energy are: 
                        i. Biomass  
                        ii. Sun 
3. Biomass refers to the mass of living things in an area. The decomposition of the remains and waste of living things by bacteria produces a gas called methane. Methane can be used as a fuel.

4. There are two ways to tap solar energy to produce electrical energy.  

5. Solar cells convert energy from the sun into electrical energy

8.2 TRANSFORMER
1. A transformer is a devices used for raising or lowering the voltage of alternating current. 

2. The number of turns of wire in the primary and secondary coils determines the output voltage. 

3. A step-up transformer has more turns of wire on the secondary coil and so produces a higher voltage in the secondary coil. 

4. A step-down transformer has less turns of wire on the secondary coil and so produces a lower voltage in the secondary coil. 

The Roles of Transformer in the Transmission and Distribution of 
Electrical Power. 

1. The electrical energy produced at power stations needs to be transmitted and distributed to consumers. It is transmitted around  the country in a network of cables called the power grid. 

2. Some electrical energy is lost as heat during the transmission of electrical power. 

3. Heat is generated due to the resistance of the electric cables. 

4. The loss of electrical energy can be reduced by transmitting the electrical power at a high voltage. 

5. This is achieved by using step-up transformers. 

6. The voltage of the electrical power being transmitted is then lowered to the required voltage by step-down transformers before the electrical power is supplied to the consumers 

8.3 ELECTRICAL POWER TRANSMISION AND DISTRIBUTION SYSTEM

Components in the Electrical Power Transmission and Distribution System.

1. The components in the electrical power transmission and distribution system include: 
                                 a. National Grid Network 
                                 b. Transformer Stations 
                                 c. Switch Zones 
                                 d. Main Substation 

The Functions of the Components in the Electrical Power Transmission and Distribution System.
1. Each component in the electrical power transmission and distribution system has its specific function. 

2. The Transformer Station has transformers to step up or step down the voltage of electrical energy. 

3. The Switch Zone allows the electrical energy to be  transmitted through the National Grid Network. 

4. The National Grid Network connects power stations at different places together and transmits electrical power to various places throughout the country. 

Advantages 
           i. Electrical energy can generated according to the time needed. Some power station can be shut down at periods when energy need is low and reconnected when energy need increases, this can save costs. 

           ii. If one of the power stations breaks down, its function can be taken over by another station in the network while waiting for the damaged station to be repaired. This avoids the cessation of electricity supply. Tryer 10

5. The Main Substation has transformers that step down the voltage of electrical power to suitable value to be distributed to its branches

Transmission and Distribution of Electrical Power from  the Stations to Consumers.
1. The electrical power produced at Power Stations in Malaysia has a voltage of 11 kV. It is then increased to 275 kV or 500 kV by step-up transformer stations. 

2. The high-voltage electrical power is transmitted through overhead cables. 

3. The electrical power then enters the Switch Zone and is transmitted through the National Grid Network to main substations at various places in the country. 

4. At the Main Substations, the voltage of the electrical power is decreased to 33 kV by step-down transformers. 

5. The electrical power is then channelled to factories involving heavy industries or other distribution Substation. 

6. At the distribution Substations, the electrical power reduced further by step-down transformers to 11 kV for the use of light industries. 

7. For the use of Towns/city or Houses, the electrical power is reduced to 240 V or 415 V either by the distribution substation.

8.4 ELECTRICAL SUPPLY AND WIRING SYSTEM AT HOME

Electrical Power Supply at Home
1. The mains voltage channelled to homes from the substation is 240 V. 

2. Two types of electric currents, namely Direct Current (DC) & Alternating Current (AC). DC is current that flows only one direction (battery).  

3. Electrical current (Alternating Current) is channelled to homes through cables. These cables consist of two types of wires, which are: 

            a. The Live wire - this type of wire carries current from the substation to home. 
            b. The neutral wire - this type of wire returns current from homes to the substation. 

4. The wiring system in homes includes the: 
            a. Fuse Box 
  • Contains fuses that melt and break the flow of current to protect  Electrical circuits from overloading or from short circuit. 
             b. Mains switch 
  • Controls the electrical supply to all circuit in a home. 
             c. Circuit Breaker 
  •  A circuit is broken in specific situations for example when  lightnings strike.  
            d. Live Wire – brown/BLACK
  • this type of wire carries electrical current to a home. 
            e. Neutral Wire - blue
  • this type of wire returns current to the substation. PMR2010 
           f. Earth Wire – green + yellow 
  • this type of wire carries leaked current to the Earth. 
           g. Electric Meter 
  • Measure the total amount of electrical energy used in a home. 
Electrical Wiring System
1. Generally, the electrical wiring at our home is the single-phase wiring. 
2. The three-phase wiring is usually used in places where the electrical energy consumption is higher. 
3. The electrical wiring system at home consists of a fuse box, electric meter, main switch, circuit breaker, main electrical panel, live wire, neutral wire and earth wire 3-pin 
4. The colour of the live wire is brown, the neutral wire is blue and the earth wire is 
yellow with green stripes. 
5. These three wires must be correctly wired to the pins 

8.5 THE COST OF ELECTRICAL ENERGY USAGE

Power and Voltage Ratings of Home Electrical Appliances.
1. Power is the electrical energy converted from one form into another, in a second. 
2. The larger the value of the power rating of a bulb, the brighter the bulb. 
3. Power is the rate of energy used. 
Energy (J) 
Power = ---------------------- 
     Time (s) 

4. Electrical power is measured in watts (W). 
1 kilowatt = 1000 W

5. If an electrical appliance uses 100 J of electrical energy in one second, then the power of the appliance is 100 W. 

6. If an electrical appliance uses 1000 J of electrical energy in one second, then the power of the appliance is 1000 W or 1 kW

The Relationship between Electrical Energy Usage Power and Time
1. An electric meter is used to measure the electrical energy used at home in kilowatt-hours (kWh). 
Energy Used (kWh) = Power (kW)  X  Time (h) 

2. 1 kWh is the energy consumed by a 100 W electrical appliance in 1 hour. 

Calculating the Cost of Electrical Energy Used
1. When calculating the cost of electrical energy usage, one kilowatt-hour is defined as a unit of electrical energy. 

2. The cost is simply the product of the number of units of electrical energy consumed and the cost per unit. 
Cost of electrical  = Energy used in units   X   Cost per unit energy used 

8.6 THE FUNCTIONS OF FUSE AND EARTH WIRE.

Type and rating of Fuse
1. A fuse is a device used to protect an electric circuit against excessive current.  
2. It consists of a wire that will melt at a certain temperature. 
3. The wire is usually made of an alloy of tin and lead. 
4. There are two main types of fuses. 

The Function of Fuses 
1. When a short circuit occurs, there is low resistance and a large amount of current flowing in the circuit. 
2. This may cause a fire and damage to electrical appliance. To prevent this, fuses are used. 
3. During a short circuit will cause the wire of the fuse to heat up and melt. The circuit then becomes incomplete and current stops flowing in the circuit. 

Determining the Suitable Rating of a Fuse for an Electrical Appliance.
1. The rating of a fuse is the value of the maximum current that is allowed to flow through the fuse without causing the wire of the fuse to melt. 

2. Fuses to be used in electrical appliances should have a rating of just slightly more than the current which the electrical appliances will use under normal working condition. 

3. For example, a fuse of 3 A may be used for an electrical appliance that operates on a current of 2.5 A.
Example: 

Determine the suitable rating of the fuse that should be used in an electric iron marked  
240 V, 2000 W. 
         Power 
Solution:  Current = ----------- 
        Voltage 
        2000 W
Current flowing through the iron = ----------------------- 
          240 V 
      = 8.33 A 

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