Course: Science and Elementary Technology, Topic: Unit 14 Energy management

General

Unit 14 Energy management
1. Study the picture below.

2. What is going on in the picture?
3. What would you advise the parents of the children to do to help them out of their problem?
14.1. Definition of energy and forms of energy
Find out
What is energy
Activity 14.1 Investigating the means of energy.
1. Look at the picture below.

2. What are the people doing in the picture above?
3. Discuss which ability is needed for work in the picture above
When you do work of any kind, you apply effort to do it.
Also, when you dig, you apply effort. The source of this effort is the energy
stored in your body muscles. So, what is energy?
Energy is defined as ‘the ability to do work’.
The various forms of energy include:
• Mechanical energy
• Chemical energy
• Thermal (heat) energy
• Electrical energy
• Electromagnetic energy
• Elastic energy
a) Chemical energy
Activity 14.2 Investigating chemical energy
Materials needed
• Fuel (charcoal, firewood or kerosene)
• A gas lighter or matches and matchbox
• A kerosene stove or charcoal burner
• Irish potatoes
What to do
1. Peel the potatoes before cooking. Are they soft or hard?
2. Put the kerosene in the stove or charcoal in the charcoal burner.
3. Light the stove or charcoal burner using a lighter or matchbox.
4. Use the stove or charcoal burner to cook the Irish potatoes.
Observe the potatoes after cooking.
5. Which is softer? Before or after cooking? Why?
• We cook potatoes (food) by using energy. The energy stored in
charcoal, kerosene or fire wood is called Chemical energy.
• Car batteries and dry cells also have stored chemical energy
which is used to run vehicles and produce electricity respectively.
b) Heat (thermal) energy
Activity 14.3 Investigating heat energy
Carry out these activities:
1. Rub your hands against one
another for some time. How do
you feel?
2. Rub two rough surfaces against one
another and then feel the surfaces.
What can you conclude from the results
of the activities above
• When we rub our hands against each other, heat is produced. We
feel warm as a result.
• When we rub rough surfaces together, heat is produced.
Note: Common sources of heat energy are the sun, electricity and
fuels such as charcoal, gas, biogas and firewood.
c) Electrical energy
Activity 14.4 Investigating of electrical energy
1. Look at the pictures below.

2. Can you identify the things in the pictures?
3. What do they require in order to work?
Electrical energy is also known as electricity. It is produced when
electrical currents flow in a conductor.
Uses of electricity
Electricity can be used to do the following things:
• Lighting bulbs.
• Driving machines in factories and industries.
• Operating electrical appliances such as radios, televisions and
computers.
• Drying things for example, harvested crops.
• For cooking.
d) Electromagnetic energy
Activity 14.5 Investigating electromagnetic energy
1. Look at the picture below
2. Try to identify the pictures shown.
Electromagnetic energy is a form of energy that is in form of magnetic
and electrical waves (also known as magnetism).
Example: Radio waves.
e) Mechanical energy
Activity 14.6 Investigating mechanical energy
1. Rub top of a table with sand paper.
2. Use a file to rub an iron bar.
3. Rub a matchstick on the side of a match box.
4. Discuss the results of your experiments above.
Energy can be stored or can be in motion. Energy of objects due to their
current position and ability to move is called mechancial energy.
f) Elastic energy
Activity 14.7 Investigating elastic energy
1. Look at the diagram below.
2. What is the person using?
3. Make your own catapult using pieces of old Tyre tubes and a Y shaped
stick. Ask your parent or your guardian to help you.
4. Play with the catapult by throwing stones.
5. How effective was the catapult at throwing stones? Compare it
to when you use your bare hands to throw stones.
• Elastic energy is a type of energy that is found in elastic materials.
Self –Test 14.1
1. What is energy?
2. Give any five forms of energy that you know.
3. Give three examples of devices that use electric current.
4. Explain briefly how you can generate static electricity.
14.2 Energy transformation (Energy conversions)
Find out
How energy is transformed from one form to another ?
Activity 14.8 Investigating energy transformation
1. Put some dry cells in a torch.
2. Put on the switch. What happens?
3. Strike a matchbox using a matchstick. What happens?
4. Blow a whistle or flute. What happens?
5. What does the experiments above tell you about energy?
Energy can be changed from one form to another. We say that the energy
has been transformed.
Remember!
Energy is transformed from one form into another but it is never
destroyed.
a) Conversion from mechanical energy to heat (thermal)
energy
Activity 14.9 Converting mechanical energy to
heat energy
1. Rub top of a table with sand paper. What happens?
2. Use a file to rub an iron bar. What do you see or feel?
3. Rub a matchstick on the side of a match box. What happens?
4. Explain the results of your experiments above.
• When person is using sand paper to rub a wooden table, the heat
is produced due to mechanical energy which in converted into heat
energy.
• The file produces heat energy. Mechanical energy is converted to
produce heat when using a file.
• The matchstick bursts into flames because of heat produced during
rubbing. Mechanical energy stored in the matchstick is converted into heat energy,
Mechanical energy------------------------- Heat (thermal) energy
b) Conversion from mechanical energy to electrical energy
Activity 14.10 Converting mechanical energy to
electrical energy
Rub a comb against your hair. Try to attract pieces of paper using the
comb. What happens?
When a comb is rubbed on hair, electrical energy is produced. This
electrical energy is called static electricity.
Mechanical energy------------------------ ` Electrical energy
(Comb rubbed on hair) (Static electricity produced)
Other common examples
Fig 14.3 Windwill converts mechanical energy to electrical energy
• In windmills – electricity is generated by using wind energy.
• In hydroelectric power stations – water flowing under the
influence of force of gravity is used to turn huge turbines to produce
electricity.
c) Conversion from chemical energy to heat (thermal)
energy
Activity 14.11 Converting chemical energy to
heat ( thermal ) energy
1. Use the stove or charcoal burner to cook Irish potatoes.
2. Observe the potatoes after cooking.
3. Where did the heat that was used to cook the potatoes come from?
4. What does this tell you about energy conversions?
Charcoal store chemical energy. During burning, this chemical energy
is transformed into heat (thermal) energy that is used to cook the food.
Chemical energy `-------------------- Heat (thermal) energy
(In fuel/ charcoal ) (Cooks food)
d) Conversion from chemical energy to electrical energy
Activity 14.12 Converting chemical energy to
electrical energy
What you need
• Dry cell • Switch •Connecting wire • Bulb
What to do
1. Set up an experiment as shown below.
2. Put on the switch. What happens to the bulb?
3. Now, put off the switch. What happens?
4. Write a report about your findings and present to the rest of the
class.
When the switch is put on, the bulb lights. This is because chemical
energy stored in the dry cell is converted into electrical energy
Chemical energy------------------- Electrical energy
(In dry cell) (In bulb)
Note: When switched off, the chemical energy is not converted hence
the bulb does not light.
e) Conversion from solar energy to electrical energy
Activity 14.13 Converting Solar energy to
electrical energy
1. Look at the picture

alongside. Have
you ever seen such
an installation in
the community
where you stay?
2. What are the
benefits of what
is going on in the
picture?

In the figure above, solar energy is used to produce electrical energy
that is used to light the house.
Solar energy --------------------Chemical energy------------------- electrical
(In solar panel) (In battery) (In bulb)
Remember!
Solar energy can also be transformed into heat energy that can be
used to heat water for domestic use, that is:
Solar energy ----------------------Heat energy
(In solar panel) (In water heater)
f) Conversion from electrical energy to thermal (heat)
energy
Activity 14.14 Converting electrical energy to
thermal energy
1. Assemble the apparatus as shown below.
2. Switch on the electric kettle.
3. Summarize the energy transformations that are involved in this
experiment.
When the switch is turned on, the electrical energy is converted to
heat energy in the kettle. The heat energy is used to boil the water
inside the kettle.
Electrical energy-------------------------------- Heat(thermal) energy
An electric iron also works in a similar
way.
Electricity possessed in electric iron
produces thermal (heat) energy which is
used to straighten the piece of cloth.
Electrical---------------------------------- thermal energy
(Electric iron) (Heat in iron)
g) Conversion from electrical energy to mechanical energy
Activity 14.15 Converting electrical energy to
mechanical energy
1. Assemble the apparatus as shown below.
2. Switch on the electric fan.
3. What energy transformation occurs when an electrical fan is
turned on ?
Some electrical appliances transform electrical into mechanical
energy e.g electrical blender, electric fan and motors among others.
Electrical energy----------------------------- Mechanical energy
14.3 Importance of energy
Find out
1. Why do we eat food?
2. What would happen if a vehicle ran out of fuel?
3. Suppose the Sun did not exist, what will happen to plants?
Activity 14.16 Investigating the importance of energy
1. Look at the picture below.
2. Observe the pictures above and discuss the importance of
using energy
We can not live without energy, for example, energy helps in movement,
in growth, as a source of light, heat, and electricity among other
uses.
• We get heat from different sources example, the Sun, from burning
fuels, electricity among others.
• Energy helps to grow .
• Many objects around us work using electrical energy and heat energy.
• Energy helps to improve the quality of lives.
• Energy support economic competitiveness.

Self –Test 14.2
1. Name any three forms of energy that you know.
2. Which form of energy is produced when we:
a) burn charcoal?
b) connect a bulb across a lemon using wires as shown below?
c) rub a file on an iron metal?
3. Describe the energy transformations that occur in a
a) Radio
b) Hydro-electric power generation station
c) When throwing a stone using catapult.
4. Distinguish between elastic and thermal energies.
5. Which energy transformations are involved in the diagram in
question (2) above?

14.4. Sources of energy
Find out
How energy is transformed from one form to another ?
Activity 14.17 Investigating sources of energy.
1. Look the pictures below.
2. Analyse the pictures above and discuss the main sources of
energy.
The common sources of energy are:
• The Sun - which is the main source of energy.
• Fuels – we burn fuel (solids, liquids and gases) to produce heat.
Examples
- Gas (or LPG)
- Diesel - Petrol
- Kerosene - Biogas
• Hydro-electric power – this is power produced from generators
driven by water. An example is Rusizi hydroelectric power
generation station.
Wind – wind power is produced from windmills. Windmills are wind driven
turbines which rotate the machines that produce electricity.
14.5. Renewable energy
Find out
1. Different sources of renewable energy.
2. The most common source of renewable energy.
3. The advantages and uses of renewable energy
Energy sources can be renewable or non-renewable. Renewable
energy sources are those that cannot get finished. They can actually be
recycled or reused. Examples include:
• Sunlight
• Wind
• Water or hydroelectric power
• Energy from ocean waves
• Geothermal power
• Solar power
• Bio-fuels (trees which can be planted to replace cut ones)
a) Solar energy
Activity 14.18 Visit to a solar power generation plant
Make a visit to a nearby solar energy installation.
1. Find out how solar power works.
2. Find out about the components of a solar power installation.
3. Enquirer about the importance of solar power.
4. Draw a sketch of what you observe in your notebook.
The Sun is the main source of energy. This is what is called solar energy.
It is a renewable source of energy. Look at the diagram below.
The various components of a solar power installation are:
• Solar panels – These trap solar energy from the Sun.
• Solar battery – stores charge in form of chemical energy following
conversion of light energy from the Sun.
• Inverter – converts direct current (D.C) - which is the form in
which chemical energy is stored in the battery to alternating current
(A.C) - which is the form that can be utilised by the bulbs and other
electrical equipments.
• Bulb – the load. It converts electrical energy into light energy which
enables us to see.

Uses of solar energy
1. All crops and plants depend on energy from the Sun to make their
food.
2. Solar energy is a source of warmth and light.
3. Heat energy from the sun is used to dry clothes and grains.
4 Solar panels are used to heat water in solar heaters.
5. Heat energy from the Sun is used to dry harvested food crops using
solar drier. They can also be dried by placing them directly under
sunlight.
6. Heat energy from the Sun causes evaporation in the water cycle.
This eventually provides us with rain.

Maintenance of solar installation
• Solar panel is held every time firmly in a safe position.
• Solar panel is exposed to maximum sunlight by removing all litter
that may fall it.
• Solar repair and replace the faulty parts of solar plant.
b) Biogas
Activity 14.19 Visit to a biogas plant
Visit to a nearby biogas generation facility.
1. What are the components of a biogas digester.
2. Explain the process of producing biogas and the challenges faced
in operating digester.

Biogas is produced in a special unit called biogas digester. Water and
cow dung or other materials used to produced biogas are mixed in the
digester. From the digester, a pipe is connected to the bulb or the cooker
where the biogas is intended for use.
Activity 14.20 Making a biogas plant
You will build your own biogas digester in this activity.
Materials
• 3 containers.
• Enough cow dung and water mixed in the ratio of 4:5:1.
• A long wire and a pipe .
• A delivery tube (rubber) of about 60 m long.
• Candle wax, plasticine or clay.
What to do
1. Set the biggest drum of the three with open end facing up.
2. Add the cow dung-water mixture.
3. Cut open end of the second drum to make three stands. These
stands should be about 7 cm long.
4. Make a hole on the extreme right of the closed end (bottom).
5. Make another hole (pipe-size) on the extreme left.
6. Place the small drum upside down into the large drum. Tie it with
wires to keep it in central position.
7. Insert the pipe with bigger diameter through the bigger hole.
8. Insert the delivery tube through the hole on the small drum.
9. Make a hole the size of delivery tube at the top right side of the
third tin. Seal round it with wax to close all the spaces. Connect
the delivery tube from the first tin to this tin.
10. Connect this tube to a tap (regulation of gas).
11 After one week, connect the tube to the gas cooker open the tap
and light the matchbox.
The gas produced from animal dung mixed with water is called methane
The bacteria present in the mixture breaks down the organic materials
to produce the gas. The gas is burnt to produce flame. The gas burns with
a blue flame.
Domestic uses of biogas
1. Biogas can be collected and
stored in gas cylinders for
domestic use. The remaining
waste is used as manure.
2. At home the biogas is used
in cooking and as a source
of light. It can also be used
to warm the room when it is
cold.
Advantages of installing a biogas plant
1. Biogas unlike petroleum products such as kerosene, firewood
and charcoal is a cleaner source of energy hence good for our
environment.
2. It is less cheaper unlike other sources of energy such as fuels. It
will only cost more money during installation but once you have
installed, no costs are incurred,
3. It is more convenient to use than other energy sources.
4. Biogas can be produced by anybody with minimum training.

Advantages of using renewable energy
1. They are cheap hence can be afforded by many families.
2. They do not pollute the environment that is, they are environmental
friendly.
3. They help us to conserve non-renewable sources of energy.
4. They are readily available and in abundance.
5. They, help to conserve trees, thereby conserving the environment.
6. Renewable energy sources are convenient to use.
Remember!
• Conserving energy by using renewable sources
Self –Test 14.3
1. Name five sources of energy.
2. Distinguish between renewable and non-renewable sources of
energy.
3. Many solar types of equipment are painted black. Give a reason
for this.
4. Name four components of a solar power installation and give
their uses.
5. Suggest three ways in which cow dung can be used as a source
of fuel.
6. What name is given to the gas that burns in biogas as a source
of fuel?
7. Give some advantages of using renewable sources of energy as
opposed to non-renewable sources.
UNIT TEST 14
1. What is energy?
2. When we eat, we get energy to work and to do other things.
What form of energy is contained in food?
3. Why would a vehicle without fuel stop moving?
4. Describe the energy transformations involved in the following
diagram.
5. You have been employed in an organisation dealing with
environmental conservation in your home area. Assume you have
been asked to explain to the people the importance of planting
trees, what are some of the points you would give?
6. Solar panels change Sunlight into ________ form of energy.
A. Heat B. Sound C. Chemical D. Electrical
7. Which of the following is not a use of animal dung?
A. Production of biogas B. Making charcoal balls
C. Fuelling improved jikos D. Making of solar panels
8. Energy stored in fuels is ________________ energy.
9. Describe a simple experiment you would use to demonstrate the
existence of thermal energy.
10. a) What is the difference between static and current electricity?
b) Describe how you would produce static electricity using a
comb.
11. When a bulb is lit using dry cells, the energy changes that take
place are:
A. Chemical----------- electric--------- light ------------heat
B. Chemical----------- electric--------- kinetic--------- heat
C. Chemical----------- heat -------------light -----------electric
D. Chemical----------- electric--------- heat----------- light
12. Find out and circle eight forms of energy in the puzzle below.
13. When food is digested, chemical energy is changed to _______.
A. Light and heat B. Heat and motion
C. Electric and motion D. Electric and heat
14. Which one of the following correctly describes the energy
transformations in a simple electromagnet?
A. Electromagnetic electric chemical attraction
B. Chemical electric electromagnetic attraction
C. Chemical electrical electromagnet
D. Electrical chemical attraction electromagnetic
15. Write true or false.
a) A magnet gives electromagnetic energy. _______________
b) Ocean waves is an example of a renewable source of energy.
__________
c) An inverter stores charge in solar panel installations.
___________
d) A biogas digester does not require a slurry pit. __________
16. Plan and execute a project on biogas digester at home. Use the
biogas to cook a variety of foods?
17. Mention ways you can use to conserve energy in your community.

Science and Elementary Technology

General

Unit 14 Energy management

Unit 14 Energy management

Table of contents