Science and Technology Standard Four PDF

 FOR ONLINE USE ONLY DO NOT DUPLICATE Science and Technology Standard Four Pupil’...

 FOR ONLINE USE ONLY DO NOT DUPLICATE Science and Technology Standard Four Pupil’s Book LY N O SE U E N LI N O R FO Tanzania Institute of Education SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 1 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE © Tanzania Institute of Education, 2019 Published 2019 Reprinted 2021 LY ISBN 978 - 9987- 09 - 110 - 2 N O Tanzania Institute of Education P.O. Box 35094 Dar es Salaam SE U Mobile number: +255 735 041 170 +255 735 041 168 E E-mail: [email protected] Website: www.tie.go.tz N LI N O All rights reserved. This book may not be reproduced, stored in any retrieval system or transmitted in any form or by any R means, electronic, mechanical, photocopying, recording or otherwise without prior written permission of the Tanzania FO Institute of Education. ii SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 2 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Table of content Acknowledgements...........................................................v Introduction........................................................................ vi LY Chapter One Environment.......................................................................... 1 N Chapter Two O Energy................................................................................. 13 Chapter Three SE Energy and its use.............................................................. 35 U Chapter Four Water.................................................................................... 53 E Chapter Five N Communication................................................................... 62 LI Chapter Six N Scientific experiments.........................................................71 O Chapter Seven Body immunity..................................................................... 83 R Chapter Eight FO Diseases............................................................................ 91 iii SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 3 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Chapter Nine Human Immunodeficiency Virus (HIV) and Acquired Immunodeficiency Syndrome (AIDS)..............................105 Chapter Ten First aid..............................................................................111 Chapter Eleven LY The digestive system....................................................... 116 N O SE U E N LI N O R FO iv SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 4 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Acknowledgements Tanzania Institute of Education (TIE) would like to acknowledge the contributions of all organisations and institutions which participated in the design and development of this textbook. Writers: Dr Felista Urasa, Dr Akwilina Mwanri, Dr Nahonyo Cuthbet, Dr Winifrida Kidima, Mr Japhet LY Mwagumbo, & Mr Swalehe Mweyo (Biology), Dr Egidius Rwenyagila, & Ms Auguster Kayombo (Physics), Dr Joseph Philip (Chemistry), Mr N Ayubu Sanga, & Mr Watson Mtewele (ICT) O Editors: Prof. Stelyus Mkoma (Chemistry), Dr Emmanuel Sulungu (Physics), Dr Charles Lyimo, & Dr Jamal SE Jumanne (Biology), Dr Frank Tilya (ICT), Dr Deoscorous Ndoloi, & Dr Rodrick Ndomba (Language) U Designer: Mr Kuyonza Kini Kuyonza E Illustrator: Alama Art and Media Production Co. Ltd. N Coordinators: Mr Japhet Mwagumbo, & Mr Watson Mtewele LI TIE also extends its sincere gratitude to primary school teachers N and pupils who participated in the trial phase of the manuscript. Likewise, the Institute would like to thank the Ministry of Education, O Science and Technology for facilitating the writing of this textbook. R FO Dr Aneth A. Komba Director General Tanzania Institute of Education v SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 5 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Introduction This is the second book in a series of five books for Science and Technology for primary schools. The text book is prepared according to the 2016 Science and Technology Syllabus for primary schools issued by the Ministry of Education, Science and Technology. The book aims at developing pupil’s competences in investigations, innovations and curiosity. It is also geared to LY develop creativity and the use of scientific and technological skills in day-to-day activities. The book comprises of eleven N chapters that have been prepared to carter for the current subject syllabus. These chapters are Environment, Energy, Energy and O its use, Water, Communication, Scientific experiments, Body immunity, Diseases, HIV and AIDS, First aid and The digestive system. The book uses illustrations and practical activities to SE help you in developing the required competencies. Also, the book is intended to help you in developing competencies in reading, writing and arithmetic. U E N LI N O R FO vi SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 6 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Chapter One Environment Introduction LY In Standard Three, you learnt about living and non-living things in the environment. In this chapter, you will learn about environmental safety and activities that threaten the N safety of the environment. You will also learn about activities O that maintain the safety of the environment. Meaning of environment SE Environment includes all things that surround us including living and non-living things. Examples of living things are animals and U plants. The non-living things include sand, stones, air and water. Safe environment E Safe environment for living things is one that has not been polluted or affected by other environmental threats. Such N environment allows living things to live and flourish. A polluted environment is not safe for living things because it affects their LI health and growth. N The environments that are safe for living and growth of living things include clean soil, air, and water. If the environment is O polluted it becomes unsafe for living things. R FO 1 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 1 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Observe Figure 1, then answer the questions in Activity 1. LY N O SE Figure 1: Environmental pollution Activity 1: Investigating the activities that threaten U the environment 1. Which activities shown in Figure 1 can threaten the safety E of living things? N 2. Suggest ways of preventing environmental pollution. LI Soil pollution Carefully read the passage below, then answer questions in N Exercise 1. O One day a teacher at Kidete Primary School gave his pupils an assignment. The assignment involved investigating the activities that cause soil pollution. Pupils had exercise books, pens, and R pencils for recording their findings. The teacher instructed the FO pupils to submit their work immediately after completion of the investigation. After submitting their work, the teacher chose one of the pupils named Shukrani and they had the following conversation: 2 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 2 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Teacher: In your investigation, which activities can threaten the safety of the soil? Shukrani: I discovered that there is uncontrolled burning and dumping of solid waste around the environment. Teacher: Fine. What objects did you find scattered in the environment that caused soil pollution? Shukrani: I saw plastic bags, plastic containers, bottles, and LY iron nails. Other objects were razor blades, pieces of iron sheet and broken glass. These objects were scattered everywhere in the environment. Also, I N saw sewage from residential houses being drained into the soil. O Teacher: What effects do you think these scattered objects have on living things? SE Shukrani: These objects affect the health of animals and plants in different ways. They also provide breeding sites for mosquitoes which cause malaria. In addition, U the sewage from residential houses may facilitate the spread of diseases such as cholera and typhoid. Teacher: Very good. What should be done to solve the E problem? N Shukrani: We are supposed to clean the littered areas by LI collecting and keeping all the solid waste in dustbins. Then, the solid waste should be safely disposed off N or burnt. We can also dig a hole in the ground and bury the solid waste which can decompose. O Teacher: Where can we safely burn the solid waste? Shukrani: We can burn solid waste in a pit. We can also use R special furnaces constructed for that purpose. FO Teacher: Good. Burning of waste is regarded as a good method of reducing the quantity of wastes. However, it releases a variety of toxic pollutants that affect health and the environment. Therefore, it is important 3 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 3 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE to burn waste far away from residential houses. Can you mention other types of waste that can pollute the soil? Shukrani: Household waste such as waste water and sewage effluent. Teacher: You are right. Oil spill from vehicles and heavy machinery can also affect the soil. LY Shukrani: Thank you teacher. I promise to be a good ambassador in protecting the environment. Teacher: Thank you Shukrani. I believe that you and your N fellow pupils will be good ambassadors in protecting the environment. Safe environment including soil O is a suitable habitat for microorganisms that fix nitrogen and help decomposition of organic matter SE which is used by plants. Therefore, there is a need for conserving the soil. U Exercise 1 Answer the following questions in your exercise book. E 1. What have you learnt from the conversation between the teacher and Shukrani? N 2. List activities that can cause soil pollution. LI 3. What are you supposed to do to keep your environment clean? N 4. Describe the effects of disposing things that cannot O decompose. 5. Explain what you can do at home to keep the environment safe and clean. R FO Water pollution When you observe the environment in which you live, you will find that some people throw waste in water sources. Domestic sewage, industrial and mining effluents are also released into 4 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 4 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE the water sources. Wastewater from industries, factories and mines may contain harmful and toxic chemicals. Releasing this toxic waste pollutes water bodies and the environment. Daily human activities may pollute water sources. These activities include washing of clothes, bathing, defecating, urinating and farming near water sources or along river banks. Also when animals pass along or across rivers, ponds, wetlands and lakes can pollute the water. LY Polluting water sources affects people and other living things. Polluted water can cause diseases such as typhoid and cholera. Water polluted by chemicals from industries, mining and farming N activities can cause cancer. O Observe Figure 2, then answer the questions in Exercise 2. SE U E N LI N Figure 2: Activities that pollute water sources O Exercise 2 Answer the following questions in your exercise book. R 1. Which harmful effects can be caused by the activities in FO Figure 2? 2. How can you avoid the activities shown in Figure 2 that pollute water? 5 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 5 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Air pollution Air is a mixture of various gases that are found in the atmosphere. Air can be clean or polluted. Clean air has no pollutants harmful to health and environment. Polluted air has contaminants which are harmful to human beings, animals, plants and the environment. Dust, bad or noxious smell, chemicals and disease causing agents can pollute air. Human activities such as burning of LY forests and garbage can contribute to air pollution. Air pollution can also be caused by toxic smoke from industries, factories, N motor vehicles and aeroplanes. O Exercise 3 Observe Figure 3, then identify activities that cause air pollution. SE U E N LI N O R FO Figure 3: Some sources of air pollution 6 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 6 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Effects of environmental pollution Activity 2: Investigating the effects of environmental pollution Investigate your school surroundings then list the effects of environmental pollution. Read carefully the following passage, then answer the questions LY in Exercise 4. One day the teacher invited an environmental expert from Mima N Ward to visit the school. The aim of the visit was to explain the effects of environmental pollution. The expert explained that, the O environmental pollution causes death of animals and plants. The deaths are due to either air, water or soil pollution. Also, release SE of wastewater from residential houses, industries, and factories to water bodies affects organisms living in it. The expert continued saying that polluted water can be infested U with disease causing organisms. Disease causing organisms in infested water can cause diseases such as cholera, typhoid and schistosomiasis. E Chemicals from industries, mining and agricultural activities can N cause soil pollution. The contaminated soil affects plants and animals. LI The expert also explained that cutting of trees increases the amount of carbon dioxide gas in the atmosphere. The gas N is used by plants to manufacture their own food through the O process of photosynthesis giving out oxygen gas which is used by human beings and other animals. Similarly, burning of forests increases the amount of carbon dioxide in the atmosphere. R However, excessive carbon dioxide is harmful to the environment FO as it contributes to global warming. Pupils asked the expert about the effects of smoke from industries or factories to the environment. The expert explained 7 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 7 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE that smoke from industries or factories affects human lungs and causes diseases such as lung cancer. Other diseases such as coughing and flu are also caused by air pollution. The expert thanked the pupils for their attention and advised them to protect the environment. The teacher thanked the expert for the nice presentation which increased pupils’ awareness about environmental pollution. LY Exercise 4 Answer the following questions in your exercise book. N 1. Name diseases that can be caused by water pollution. 2. Which activities when performed in the environment O may lead to the death of living organisms? 3. What can you do to keep your home environment safe and clean? SE 4. Explain what will happen if we do not clean and keep U the environment safe. Protecting the environment E It is important to keep our environment clean and safe. Solid waste which can decompose and that which cannot decompose N should be kept separate. Solid waste which does not decompose but can be recycled, such as pieces of glass and plastic should be LI taken to factories for recycling. Solid waste that can decompose N such as food remains, paper, grass and leaf litter can be buried in the ground where they will decompose and form manure. O It is important to direct wastewater to established sewage systems. If there is no such system, the wastewater should R be kept in special wastewater pits. When the wastewater pits are full, wastewater bowsers should collect and dispose off the FO wastewater in designated locations. In areas where there are no wastewater bowsers, the filled wastewater pits should be covered and replaced by new ones. 8 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 8 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Observe Figure 4, then answer the question in Exercise 5. LY N O Figure 4: A pupil dumping waste in a dustbin Exercise 5 SE What have you learnt from Figure 4? U Observe Figure 5, then answer the questions in Exercise 6. E N LI N O R FO Figure 5: Pupils planting and watering tree seedlings 9 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 9 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Exercise 6 Answer the following questions in your exercise book. 1. List the activities in Figure 5 that are being done by pupils. 2. Explain the importance of the activities shown in Figure 5. 3. Can you do the activities shown in Figure 5 at your school? LY Cleanliness and safety of air Observe Figure 6, then read the conversation between Neema N and Musa. O SE U E N LI N O Figure 6: A clean environment Neema and Musa are pupils from Miembeni Primary School. R One day while on their way home from the school, Neema started a conversation, as follows: FO Neema: Why is it advised to plant trees in our environment? 10 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 10 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Musa: Because trees are important to the life of living things. Neema: What makes them important? Musa: Trees are important because we get firewood, charcoal, oxygen, fruits and shade from them. Also, trees provide medicines, timber, and a habitat for birds, animals and insects. LY Neema: Thank you Musa. I am pleased to know the importance of planting and keeping trees in our environment. If so, why then do some people cut N trees? Musa: People cut trees for various purposes. Trees are O cut for firewood, charcoal and building materials. Neema: If people continue cutting trees for these purposes Musa: SE without replacing them, what will happen? Prolonged cutting of trees can cause desertification. Forest fires pollute the air by increasing the amount U of carbon dioxide gas in the atmosphere. Neema: Thank you Musa for your explanation. Is charcoal making the only cause of air pollution? E Musa: No. There are other causes of air pollution. These N include dust and bad smell from sewage. Smoke from factories, poorly maintained vehicles and LI heavy machinery that use fuel can also cause air pollution. N Neema: Thank you Musa for your explanation. It is good to O educate the community on how to keep air clean. Musa: Exactly, the community is responsible for maintaining cleanliness and safety of the environment. People R should not burn forests. It should also reduce FO charcoal making and use alternative clean energy sources such as gas, solar power, biogas, wind, and hydroelectric power. 11 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 11 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Exercise 7 Answer the following questions in your exercise book. 1. What have you learnt from the conversation between Neema and Musa? 2. Explain the effect of using poorly maintained vehicles which produce a lot of smoke. 3. What effects do charcoal making have on people? LY 4. Which source of energy do you use for cooking at home? N 5. Describe what will happen to the environment if people continue using firewood and charcoal as sources of O fuel for a long time. 6. What kind of activities can cause air pollution at your school? SE Exercise 8 U Answer the following questions in your exercise book. 1. Describe the effects of disposing wastewater into water sources. E 2. List human diseases which are caused by air pollution. N 3. Explain the importance of planting trees. LI 4. What should be done to reduce the use of firewood and charcoal as fuel? N 5. How can you maintain clean and safe air in your environment? O 6. List the types of waste materials that can be recycled. R Vocabulary Recycling - the process of using waste material to form FO new products Fuel - any material that is burnt to produce energy 12 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 12 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Chapter Two Energy Introduction In Standard Three, you learnt about the uses and the LY importance of three types of energy. These types of energy were heat energy, sound energy and light energy. In this chapter, you will learn about electrical energy. You will learn N about the sources, uses and importance of electricity in our O daily lives. You will also learn the concept of ‘optics’ which includes the general properties of light energy. Electrical energy SE The sources which generate electricity are waterfalls, sunlight, U wind and fossil fuels. All these energy sources are converted into electricity using different energy conversion systems. These energy conversion systems include solar panels, wind turbines E and water turbines, dynamo and fueled generators. N Generating electricity using waterfalls LI Electricity generated using waterfalls is called hydro-electricity. Hydro-electricity is generated when water falls from a height to N water turbines connected to an electric generator. Water turbines are devices which rotate when water falls on them, in turn the O turbines generate electricity. A hydro-electric power plant uses water stored in a dam or water R reservoir. The dam is constructed in such a way that a barrier is put to collect water. Then, the water stored in the reservoir FO is allowed to fall on blades of a turbine connected to the shaft. The falling water on the blades of the turbine rotates the shaft which activates a generator to produce electricity. 13 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 13 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Hydro-electricity is generated in well-engineered locations called water dams. In Tanzania, hydro-electricity is generated at Kidatu and Kihansi in Morogoro and Mtera in Iringa. Other areas where hydro-electricity is generated are Nyumba ya Mungu in Kilimanjaro and Pangani and Hale in Tanga. Figure 1 shows a picture of water falls capable of producing hydro-electricity. LY N O SE U E Figure 1: Waterfalls that could be used to generate electricity N Generating electricity using sunlight Electricity generated using sunlight is called solar electricity. This LI type of electricity is obtained from sunlight using a solar panel. The panel collects sunlight and converts it into electricity. The N electricity can only be produced during the daytime, when there O is sunlight. In order to use solar electricity, the solar panel is connected to energy storage systems such as batteries. Figure 2 shows the panel on the rooftop of a house. R FO 14 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 14 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Solar panel LY N O Figure 2: The solar panel on a rooftop of a house Generating electricity using wind SE This type of electricity is generated when strong wind blows on U a set of blades forcing them to rotate. The blades are connected to wind turbines which are connected to an electric generator. Electricity is generated when strong wind blows on the blades E which rotates turbines connected to electric generators. A place N where wind electricity is generated by many wind turbines is called a wind farm. LI These locations are called wind farms because the wind turbines are scatted on a large area. Some potential areas for constructing N large wind farms capable of producing considerable electricity O in Tanzania are Singida and Makambako. A wind turbine used to generate electricity is shown in Figure 3. R FO 15 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 15 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Wind turbine LY N Figure 3: A wind turbine used to generate electricity O Generating electricity using fossil fuels Electricity can also be generated using fossil fuels. Fossil fuels SE include coal, natural gas, petroleum and diesel. When the fossil fuel is burned, it produces heat energy. The heat energy is then converted into electricity using electric generators. The generators can be small or large depending on the needs. U Currently, they are being replaced by generators which use cheap natural gas that is abundant in Tanzania. E Examples of generators which use natural gas are found in Mtwara and at Kinyerezi in Dar es Salaam. Small electric N generators such as shown in Figure 4 use petrol to generate small scale electricity. The generated small scale electricity LI is used in schools, homes, dispensaries, conference halls, mosques and churches. N O R FO Figure 4: Small scale fuel electric generator 16 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 16 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Transmission and distribution of electricity The electricity generated from different sources needs to be distributed to different places. These places include homes, industries, workshops, schools, hospitals and many others. The transmission of electricity requires special pathways. A large national scale pathway is called the power grid. The pathways at small scale found in homes and science laboratories are called electric circuits. An electric circuit is LY a path through which electric current flows. It consists of the source of electricity, connecting wires or cables, switches and electrical appliances or devices. Electricity flows only if the circuit N is properly connected and a switch is turned on. O Experiment: To investigate if dry cells can produce electricity Aim: To show that dry cells produce electricity SE Materials: Two dry cells, three pieces of connecting wire, switch, tape, light bulb U Procedure Use the following steps to complete the circuit. 1. Connect the dry cells as shown in Figure 5. E 2. Using a tape connect one end of the wire to the N terminal with a plus (+) sign (positive terminal) of the dry cell. Connect the other end of the wire to the switch. LI 3. Connect one end of another piece of wire to the second end of the switch and the other end to the N middle metallic part of the bulb. O 4. Connect one end of the third wire to the bottom of the bulb and the other end of that same wire to the terminal with a minus (–) sign (negative terminal) of the dry cell. R 5. Turn ON the switch and then turn it off. FO 6. Remove all the dry cells and connect the wires without the dry cells. 7. Turn ON the switch and then off. 17 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 17 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Switch Positive Bulb terminal Dry cell LY N Negative terminal O Wire SE Figure 5: An electric circuit 8. Write a report of the experiment based on the following questions: U (a) What did you observe when you turned ON the switch? E (b) What did you observe when you turned off the switch? N (c) Did the bulb light when you connected the wires LI without the dry cells? (d) What was the source of electricity in your electric N circuit? O Conversion of electricity into other forms of energy Electrical energy can be converted into other forms of energy R using different devices. For example, a torch can convert FO electrical energy of a dry cell into light energy and heat energy. An electric heater can produce heat energy when connected to an electric socket. An electric bell converts electric energy into sound energy. 18 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 18 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Use Figures 6(a), 6(b) and 6(c) to answer the questions in Activity 1. LY N O SE Figure 6(a) U E N LI N O R FO Figure 6(b) 19 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 19 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE LY N O SE Figure 6(c) U Activity 1: Investigating the uses of electricity in daily life 1. Name the electric appliances shown in Figures 6(a), 6(b) and 6(c). E 2. Mention the forms of energy generated by the electric N appliances shown in Figures 6(a), 6(b) and 6(c). LI Uses of electricity N Read the following passage carefully, then answer questions in Exercise 1. O One day, Rehema and her friends were walking from school. R On the way, they saw a big truck outside the Ward Executive Office. They also saw a group of excited youths outside the office FO cheering loudly. Two of the youths went and opened the door of the truck and saw many large and small boxes. 20 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 20 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE They unloaded the boxes from the truck and carried them to the office. Rehema and her friends went to the office to find out what was in the boxes. Rehema asked the officer, “What do the boxes contain?”. The officer told them that the boxes contained solar panels and associated electrical components such as batteries, electrical cables and sockets. “The components in the boxes will be used to install a solar system in the village. Very soon, our village will start using LY electricity that is produced directly from sunlight”, the Ward Executive Officer told Rehema and her friends. One week later, many people in the village had installed the N solar panels on the rooftops of their houses. The people in O Rehema’s village started using solar electricity for different home applications. Rehema was also very happy as she started using electricity for different applications at her home. SE Rehema used electricity to light her room for reading and doing her school homework at night as shown in Figure 7. She was also able to watch television and listen to the news on the radio U both powered by solar electricity. E N LI N O R FO Figure 7: Rehema in her room reading 21 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 21 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE In addition, as shown in Figure 8, Rehema was able to iron her clothes quickly using an electric iron and report to school on time. LY N O SE U Figure 8: Rehema ironing clothes using an electric iron One day Rehema requested her teacher if she could be given an opportunity to explain to the class how the village had E benefited from solar electricity. The teacher permitted Rehema N to explain the benefits of solar electricity. She said that, electric cookers use electricity for cooking. Refrigerators which are used LI for preserving foods and blenders for making juice also use electricity. In addition, water pumps and hair clipper machines N use electricity. O The teacher further explained that electricity is also used in welding and running machines in industries, hospitals, factories, workshops and laboratories. Therefore, many people can be R employed in those areas with activities that depend on electricity. FO The teacher added that electricity is useful only when used with care. When used carelessly, electricity can cause damage. Electrical faults including inappropriate connections can cause 22 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 22 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE fires, explosions and even death. The pupils thanked Rehema and the teacher for the information on the uses, benefits and dangers of electricity. Exercise 1 Answer the following questions in your exercise book. 1. Mention the benefits of electricity as described by Rehema. LY 2. What are the uses of electricity as described by the teacher? N 3. What was the source of electricity that was installed in Rehema’s village? O 4. What are the other benefits of electricity in our environment and lives? Exercise 2 SE U Answer the following questions in your exercise book. 1. Mention any four sources of electricity. E 2. What makes an electric bulb light when connected to dry cells? N 3. Mention any four domestic appliances that use electricity. LI 4. Mention any three areas where electricity is used. 5. What are the possible harmful effects that can be N caused by electric faults? O 6. What are the benefits of using electricity in our daily life? R Activity 2: How to make an electric torch Materials: hard paper, two dry cells, 30 cm piece of wire, FO torch bulb, adhesive paper tape and a pair of scissors 23 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 23 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Procedure 1. Cut a piece of hard paper (Figure 9 (a)) long enough to cover the length of two dry cells. LY Figure 9 (a): Piece of hard paper N 2. Cut a piece of wire (Figure 9 (b)) long enough to connect the positive and negative terminals of the O two connected dry cells. SE U E Figure 9 (b): Piece of wire 3. Place the piece of wire along the connected dry cells. N Wrap the connected dry cells and wire with the hard LI paper. Secure the hard paper wrapping using an adhesive tape as shown in Figure 9 (c). N O R FO Figure 9 (c): Dry cells and wire wraped with hard paper 24 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 24 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE 4. Use the tape to connect the wire to the negative terminal of the connected dry cells. 5. Connect the other end of the wire to the metallic part of a bulb. 6. Connect the positive terminal of the bulb to the positive terminal of the dry cells as shown in Figure 9(d). What do you observe? LY N O SE Figure 9 (d): An example of an electric torch 7. Detach the bulb from the positive part of the battery. U What do you observe? In this experiment, you have observed that the bulb gives light E only when the dry cells, the wire and the bulb are properly N connected. This connection causes electric charges from the dry cells to flow in the circuit. The flow of charges in the circuit LI is called electric current. When this current flows through the bulb, the bulb gives out light and heat energy. N Light energy O Light is a form of energy which can be produced by natural sources like the sun. Light can also be produced by converting R some other forms of energy. For example a torch bulb converts electrical energy into light energy. Light behaves differently when FO it falls on different objects. Light can be blocked or can pass through some objects. 25 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 25 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Transparent and opaque objects Objects that allow light to pass through them are called transparent objects. An example of a transparent object is a piece of glass. Glass is transparent because it allows us to see objects behind it. Objects that do not allow light to pass through them are called opaque objects. Examples of opaque objects are wood, books and brick walls. LY Exercise 3 Using Figure 10, name the objects that allow and those which do not allow light to pass through them. N O SE U E N LI Figure 10: Transparent and opaque objects N Activity 3: To determine the ability of different objects to O block or allow light rays to pass through R Materials: Torch, dry cells, an empty glass, a black colored plastic cup, a white piece of cloth, eye FO glasses, a piece of a plane glass, table, a piece of wood, a glass full of water and a book 26 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 26 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Procedure 1. Insert the dry cells into the torch compartment and switch it on. Make sure it gives out light. 2. Enter a dark room with the torch switched on and arrange all the available materials on top of the table. 3. Illuminate the book with the light and observe if the book blocks or allows light to pass through. LY 4. Repeat step number 3 for all the objects on the table. N 5. Use the following questions to write down the results of the experiment. O (a) Which objects allowed light rays to pass through? (b) SE Which objects did not allow light rays to pass through? U (c) What did you observe when the light rays fell on the surface of each object? E Properties of light Light travels in a straight line. N Activity 4: To observe how light travel LI Materials: torch, dry cells, table and hard paper N Procedure 1. Make a small hole on hard paper and place the hard O paper on the table at a distance from a wall. Note: Ensure the hole is small. R 2. Stand in such a way that the hard paper with a hole is FO between you and the wall as shown in Figure 11. 3. Illuminate the hard paper containing the hole using the torch light. 27 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 27 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE LY N Figure 11: Observation on how light travels in a straight line O In Figure 11, the hard paper blocked light rays and produced a shadow on the wall. The part with the hole did not block light rays. The hole SE allowed the light rays to pass through straight to the wall. This shows that light travels in a straight line. When light meets different media, it shows different properties such as formation of shadows, reflection U and bending. Formation of shadows E A shadow is produced when an object blocks the path of light rays. The shapes of shadows resemble the shapes of objects blocking the N light rays. LI Read the following passage carefully, then answer questions in Exercise 4. N Mwajuma and her friends are in standard four at Shaurimoyo Primary O School. One day the teacher taught them about the properties of light. He told them that one of the properties of light is that it travels in a straight line. When light falls on opaque objects, it is blocked and R produces a shadow. FO The teacher instructed the pupils to carry out an activity to help them observe what happens when light is blocked. He said, “tomorrow morning, stand in an open place with the sun shining on your back 28 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 28 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE and observe what happens in front of you. Again, with the sun shining on your back, take a ball and stretch sideways the hand with the ball and observe what you see on the ground.” The next morning when there was sunshine, Mwajuma and her friends went to the school playground in order to carry out the experiment. The pupils stood as instructed by the teacher and saw dark shapes as shown in Figure 12. They noted down what they saw and returned to the classroom. LY N O SE U Figure 12: Observing shadows during the day The teacher came into the classroom and asked them to explain their observations. Kalunde said, “In front of me, I saw a dark E shape on the ground.” Mwajuma added, “I saw a shape which N resembles my own body.” Another pupil said, “I saw my own shape along with the shape of the ball I was holding in my right LI hand.” Then, the teacher said, “What you saw on the ground are N called shadows.” Shadows are formed when light is blocked O with opaque objects. They are produced when light is blocked from travelling in a straight line. The teacher explained further, “Shadows change direction and size depending on the location R of the light source.” Mwajuma and other pupils enjoyed the lesson because they understood how shadows are produced. FO 29 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 29 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Exercise 4 Answer the following questions in your exercise book. 1. What did the teacher ask the pupils to investigate? 2. What results did Kalunde and Mwajuma report after the observation? 3. Explain how a shadow is produced? LY 4. Can a shadow appear in a dark room? Explain. N Activity 5: To observe how shadows are produced O Materials: A cup, a book, a chair and a table Procedures SE 1. Take a cup and a book and expose them to sunlight. What do you observe? 2. Place the table and the chair outside in the sunlight. U 3. Look under the table and the chair. What do you observe? Reflection of light rays E Reflection of light refers to an act of light rays bouncing back N off shiny surfaces or substances. The reflection of light rays results into the formation of an image. An example of an object LI with a shiny surface is a mirror, such as shown in Figure 13. N O R FO 30 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 30 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE LY N O SE Figure 13: Formation of an image on a plane mirror U Exercise 5 Explain how an image is formed on a plane mirror. E Activity 6: Investigation on the reflection of light rays N Materials: A plane mirror, a table and a pen LI Procedure 1. Place a plane mirror upright on a table. N 2. Place a pen in front of the plane mirror and look at the O mirror. 3. Write down what you observe in steps 1 and 2. R 4. Explain the results of the experiment. FO When light rays fall on smooth surfaces, they are reflected. Reflection of light produces images on shiny smooth surfaces. 31 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 31 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Bending of light rays Light rays bend when they pass from one transparent medium into another transparent medium. For example, light rays bend when moving from air to water. In reality, we do not observe bending of light rays but we observe its outcome. Activity 7: Investigation of bending of light rays Materials: A beaker or transparent bowl, clear water and a LY pencil Procedure 1. Hold a pencil with part of it inside an empty transparent N bowl as shown in Figure 14. O 2. Observe how the pencil appears. 3. Pour clean water into the bowl until it is full as shown in Figure 14. SE 4. Again, observe the appearance of the pencil immersed inside the bowl containing water. U What is the difference between the appearances of the pencil before and after pouring water into the E bowl or beaker? N LI N O R FO Figure 14: A pencil immersed in water to show the effect of bending of light rays 32 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 32 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE When a light ray passes from air into water, it bends. This bending is caused by the different properties of air and water. The effects of bending of light rays were demonstrated by the bending of a part of the pencil which was inside the transparent bowl with water. Exercise 6 Answer the following questions in your exercise book. LY 1. What happens when light rays pass from one medium to another medium of different properties? 2. Why are images formed by plane mirrors? N 3. What are the differences between surfaces that reflect O light and surfaces that do not reflect light? 4. Explain how shadows are formed Exercise 7 SE Match the items in column A with phrases from column B to U make a meaningful sentence. Column A Column B 1. Shadow (a) Bouncing back of light rays on E 2. Bending a shiny surface or substance. (b) The moon and the star. N 3. Straight line 4. Two different (c) Dark shape that occurs when LI transparent media light hits an opaque object. 5. The sun (d) Enable light to travel easily. N 6. Reflection (e) One of the properties of light. (f) The way in which light rays O 7. Image travel. (g) Results of light reflection or R refraction. (h) Causes light to bend. FO (i) Natural source of light. 33 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 33 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Vocabulary Reflection - bouncing or change of direction of light by a smooth shining surface Transparent - object or substance that permits light rays to pass through it Electron - a negatively charged particle Fault - wrong, incorrect or damaged, not working LY properly or not made correctly Media - solid, liquid or gas substances or N materials through which light travels Solar panel - device for converting sunlight energy to O electricity Image - picture or shape that appears in smooth SE shining surfaces such as mirrors. U E N LI N O R FO 34 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 34 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Chapter Three Energy and its use Introduction In chapter two, you learnt about electrical and light energy, LY and you did various experiments related to these. In this chapter, you will learn different electrical and non-electrical N equipment that are used for cooking and storage of food. The devices which you will learn about are refrigerators and O cooking stoves. Refrigerators SE A refrigerator is an appliance which preserves different stuffs U like food by cooling. A refrigerator uses electricity to operate. Importance of a refrigerator Food is kept in a refrigerator to keep it fresh for a long period E of time while preserving its taste and nutritional values. It also N saves time as there is no need for shopping for food stuffs every day. In hospitals and pharmacies, refrigerators are used LI to store medicines for similar reasons. Medicines are kept at low temperatures to retain their effectiveness. Refrigerators N are more important in areas with hot climate than those with cold climate. In days with high temperatures, people sell soft O drinks preserved in refrigerators to earn money. R FO 35 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 35 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Freezer LY Fridge N O Figure 1: A refrigerator showing different stored foods Parts of Refrigerator SE Refrigerator for foods preservation has two parts, kept at different temperatures. The first part freezes foods and the U second keeps foods cold, see Figure 1. It is important to identify which foods require freezing and which foods need to be kept cold in a refrigerator. E The freezer N The part of the refrigerator which freezes food items is called LI the freezer. In some refrigerators, the freezer is the upper compartment while in others it is the bottom compartment. N Anything kept in this part will eventually freeze. This part is used to store food that is to be preserved for longer time like O meat, fish and milk. Fresh seeds like peas or beans and other types of food stuffs that may spoil when kept under normal R temperature should also be stored in the freezer. The fridge FO The compartment of the refrigerator which does not freeze is called the fridge. This part normally has several partitions. In most refrigerators, the temperature in this compartment is below 36 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 36 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE 5 degrees centigrade. This compartment is therefore used to store foods like cooked rice, fresh or cooked vegetables, fruits and drinks. As shown in Figure 1, the door of the refrigerator has some partitions used for storing drinks and medicines. Foods that spoils quickly are not kept in the door of the refrigerator because the door does not have a cooling mechanism. LY How to use a refrigerator It is very important to use a refrigerator appropriately so that it lasts long. Every new refrigerator has a manual which instructs N users how to use it. Reading and understanding the manual O allows proper use of the refrigerator. The following are some of the important precautions to be taken when using a refrigerator: 1. Avoid to keep hot foods in refrigerators. SE Putting hot food in a refrigerator will result into an increase U of its temperature to more than the desired 5 degrees centigrade. Increased temperature favours the production of microorganisms like bacteria which may spoil foods stored in E the refrigerator. N 2. Do not switch ON and off the refrigerator frequently. LI This is because doing so slows down the ability of the appliance to perform its functions. N 3. Clean the refrigerator. O Before cleaning the refrigerator, make sure that it is switched off. Clean the compartments using water and soap. Do not use any scratching material to clean the refrigerator. Once cleaned, R dry it using a piece of soft cloth. You are also advised to clean FO any food that falls from its storage part before it sticks to the walls of the refrigerator. 37 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 37 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE 4. Place similar types of food in the same compartment. You are advised to pack vegetables and fruits in appropriate bags before storing them in the refrigerator. Do not use glass containers to store food in the freezer because glass can easily break and contaminate food. Not every food should be stored in a refrigerator. Food such as flour, uncooked rice and onions should be stored in a clean and dry safe place and not in a refrigerator. LY 5. Close the door of a refrigerator properly. Ensure the door of the refrigerator is properly closed to prevent N exchange of air between the refrigerator and the outside. O Activity 1: Switching ON and using a refrigerator Materials: water, refrigerator, thermometer and power supply Procedure 1. SE Connect the refrigerator to the power supply and switch U it ON. 2. Pour water in a bottle and measure its temperature using a thermometer. E 3. Put the bottle of water in the proper part of the N refrigerator and then close the door. 4. After 30 minutes take out the bottle of water and LI measure the temperature of the water. 5. Compare the temperature readings at step 2 and step N 4. What do you observe? O R FO 38 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 38 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE Activity 2: Constructing and using a refrigerator model Materials: Boxes, paper glue, wood glue, pair of scissors, knife, pieces of wood, rope, plastic bags, model of bottles of drinks, fruits, groundnuts, food models like fish, beef, ugali, vegetables and fruits LY N O SE U Figure 2: A model of a refrigerator Procedure E 1. Make a model of a refrigerator as shown in Figure 2. N 2. Prepare food models of fish, meat, ugali, vegetables,fruits and a bottle for drinking water. LI 3. Place the food models properly in the right compartments of the refrigerator. N 4. Explain how you placed the food models in their O respective sections of a refrigerator. R Exercise 1 Answer the following questions in your exercise book. FO 1. List three advantages of using a refrigerator. 2. List five important precautions that you should take when using a refrigerator. 39 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 39 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE 3. Name three types of food that can be kept in the non- freezing part of the refrigerator. 4. What steps should you follow when cleaning a refrigerator? 5. Match the food types in the table below to the proper parts they can be stored in the refrigerator by putting a tick (√). LY Type of food Fridge Freezer Meat Green peas N Ripe bananas O Cooked rice Milk Avocado Fresh fish SE U Cooking stoves Cooking stoves are classified according to the type of energy source used. Energy sources used include firewood, kerosene, E charcoal, gas and electricity. Cooking stoves are important because they are used for cooking food and boiling water. For N example, when you have flour, water and sugar you cannot get LI porridge without a cooking stove. Our communities use different types of stoves for cooking depending on the availability and N cost of energy sources. O Types of cooking stoves commonly used in our communities R Most stoves in Tanzanian communities use firewood and charcoal as source of energy. However, excessive use of firewood and FO charcoal requires cutting trees which results into environmental degradation. The use of charcoal and firewood produces smoke that leads to indoor air pollution. Other stoves use kerosene, gas 40 SCIENCE AND TECHNOLOGY STD 4_8 DECEMBER 2019.indd 40 30/07/2021 13:39  FOR ONLINE USE ONLY DO NOT DUPLICATE or electricity. These stoves reduce environmental pollution but their sources of energy are more expensive. Kerosene stove A kerosene stove uses kerosene as a source of energy to produce flame. There are two types of kerosene stoves. The first uses a wick and the second uses pressure. Parts of a wi