Oasis School Science and Technology -5 197 Wave Motion A material medium is required for propagation of sound. Generally, sound propagates through air. However, it propagates through liquids and gases as well. Sound propagates in the form of waves. Wave motion is a periodic disturbance travelling through a medium which is produced by a vibrating body. The disturbance in a medium is called wave. A wave motion travels in all directions through the medium in a constant speed but the particles of the medium do not move from one place to another. They only vibrate passing on energy they possess from one particle to another. During a wave motion, the medium does not move as a whole but only the disturbance travels through the medium. If we drop a piece of stone in a pond, ripples (i.e. circular waves of water) spread out in all directions on the surface of water. If we place a piece of paper on the water surface, the paper moves up and down at the same place but does not move away along with the waves. Wave Piece of paper Wave Piece of stone Water Fig: Wave motion does not carry matter with it This activity shows that the disturbance moves from one place to another but water is not carried out with it. Water molecules simply move up and down. When a stone is dropped into a pond, the energy Fig: Ripples produced in water when a stone is dropped into a pond
198 Oasis School Science and Technology -5 carried by the stone disturbs the water molecules close to it. By gaining energy from the stone, water molecules near the stone vibrate. Those vibrating molecules transfer some energy to the nearby water molecules. As a result, water waves (ripples) are formed. Waves are of two types, viz. transverse wave and longitudinal wave. Sound travels in the form of longitudinal waves. Let us perform the following activity to develop the concept of waves. Propagation of Sound Sound is produced by a vibrating body and it travels in all directions from the source. Sound requires a medium for its propagation. The sound waves coming from a vibrating body propagate through air and reach our ears. As a result, we hear the sound. Sound can propagate through solids, liquids and gases. But it cannot propagate through the vacuum. Sound can propagate through air. Air is the mixture of various gases like nitrogen, oxygen, carbon dioxide, etc. The speed of sound in air is about 332m/s. Sound waves cannot propagate in the absence of air. There is no air on the surface of the moon. So sound cannot propagate on the surface of the moon as that happens on the surface of the earth. Sound also propagates through liquids. The sound produced by dolphin, whale, etc. propagates through water. The speed of sound in water medium is about 1498 m/s. Similarly, sound propagates through the solid medium. The sound waves travel faster in solids than in liquids or gases. The speed of sound is least in gases, lesser in liquids and the most in solid medium. Fact File Sound needs material medium to propagate. It does not travel in vacuum. The more compact the medium, the higher is the speed of the sound.
Oasis School Science and Technology -5 199 Activity 8 Objective: To demonstrate the propagation of sound through a solid Materials required: Two ice-cream cups, a long thread, needle, scissors • Take an ice-cream cup and make a small hole at its bottom by using a needle. • Take a long string and insert one end of the string through the hole and tie a knot so that it does not slip back through the hole. Hi ! Hello ! Thread Fig: Activity showing propagation of sound in solids • Repeat the same process with another cup also. • Now, ask your friend to take one end of the string with the cup and you hold the other end. • Move as far from one another as possible so that the string is held tight. But do not let the string slacken. • Now, hold the cup to your ear and ask your friend to speak some words softly. Can you hear the sound produced? Repeat this activity for 3-4 times. • Now, ask another friend to cut the string in the middle. • Ask your friend to speak some words as in the previous activity. Can you hear the sound produced? What can you conclude from this experiment? Conclusion From this activity, it can be concluded that sound propagates through a solid.
200 Oasis School Science and Technology -5 Activity 9 • Visit a nearby pond. Drop a piece of stone at the centre of the pond. What happens to the surface of water? Do ripples form on the surface of water? • Now, throw a leaf on the surface of the waves in water. Does the leaf move with the waves of water? • Write down the conclusion of this activity. Activity 10 Objective: To demonstrate that sound propagates through a liquid Materials required: A bucket, water, a bell, a hammer Procedure • Take a bucket and fill it with water. • Immerse a bell into the water of the bucket and hit the bell with a hammer. Can you hear the sound? Bucket Bell Hammer Water Fig: Activity to show sound propagates through liquid • Repeat this activity for 3-4 times and hear the sound propagated through water. • What can you conclude from this experiment? Observation Sound can be heard clearly which is produced by the bell kept inside the water. Conclusion From this activity, it can be concluded that sound propagates through a liquid.
Oasis School Science and Technology -5 201 Activity 11 Objective: To demonstrate that sound propagates through a solid medium better than through a gaseous medium Materials required: A long table, a stopwatch (mechanical), notebook, pencil Procedure • Take a stopwatch that produces ticking sound and keep it on one end of a table. • Now, stand at another end of the table and try to hear the ticking sound of the watch. Can you hear the sound? Fig: Activity showing sound travels faster in solid than in gas • Now, place your ear on the table and listen to the sound of the watch. Is the sound louder than the previous sound? What can you conclude from this experiment? Observation A fainter sound is heard while hearing the sound by standing at another end of the table. But the sound of the watch is heard louder while hearing it by placing the ear on the table. Conclusion From this activity, it can be concluded that sound travels through a solid medium better than through a gaseous medium.
202 Oasis School Science and Technology -5 Effects of Noise Do you like to study in noisy environment? Of course not. In humans, noise cause loss to attention, anger and anxiety. Increase in blood pressure and headache are some common problems of noise. Loud noise of short-term result temporary hearing loss while long term exposure to large volume of sound causes deafness. Noise affects not only human beings but other organisms also. Noise forces wild creatures to leave their habitat and to search for new. It takes away the peace and calmness of places and minds. Measures to Reduce Noise There are a number of ways to reduce the effects of noise. To reduce and control the effects of noise, some measures that we can follow are listed below. i. Making the habit of speaking in soft and low volume. ii. Listening music and watching movies in small volume. iii. Using earplugs or headphones for listening music personally. iv. Avoiding unnecessary chatting in the class. v. Planting trees and vegetations around the house as they absorb sound. vi. Avoiding conversation in high volume in public places like hospitals, buses, planes, schools, restaurants etc. vii. Keeping ourselves away from the noisy environment. Reasonable Thinking Skill Reasonable Thinking Skill R T S 1. In which medium does the sound travel faster? a. Solids b. Liquids c. Gases d. Vacuum Answer: In solid medium, sound travels faster. 2. Which of the following statement is incorrect? a. Noise for one person may not be noise for others. b. Sound travels in the form of wave.
Oasis School Science and Technology -5 203 c. Loudness of sound is called pitch. d. Movement of air also produces sound. Answer: The option 'c' is incorrect. 3. What type of sound is musical sound? Sound that produces pleasing effect to us is musical sound. 4. We cannot hear sound in vacuum. Why? Sound needs material medium for propagation. Vacuum is the empty space without any material medium. So, we cannot hear sound in vacuum. 5. Illustrate two differences between noise and music. Two differences between the noise and music are: Noise Music a. It is unwanted and disturbing. a. It is pleasant to listen. b. It is unorganized and random. b. It is organized and follows pattern. c. Any instrument, devices, or activities can produce noise. c. Usually, musical instruments are needed to produce music. 6. Justify that pleasant sound for one person or group can be noise to other. Some people entertain with music produced from drums and sticks while other found it annoying. Musics like Heavy Metals are enjoyed by youngsters while others might find it as a noise. The chatting you make in the class with your friend can be pleasant to you and your company but it disturbs others to learn. It shows that pleasant sound for one person or groups can be noise to others.
204 Oasis School Science and Technology -5 Exercises 1. Choose the best answer from the given alternatives. a. A form of energy which produces the sensation of hearing is __________. i. sound ii. heat iii. light iv. electricity b. Which of the following is not a source of sound? i. radio ii. bulb iii. bell iv. guitar c. The shrillness of sound is called __________. i. loudness ii. pitch iii. noise iv. grave d. Sound cannot propagate through __________. i. solid ii. liquid iii. gas iv. vacuum e. The speed of sound in air is __________. i. 332 m/s ii. 232 m/s iii. 223 m/s iv. 322 m/s f. The speed of sound is maximum in __________. i. gas ii. solid iii. liquid iv. air g. What is required for propagation of sound? i. vacuum ii. material medium iii. electric wire ` iv. air 2. Fill in the blanks with appropriate words. a. Sound is produced due to …… of a body. b. The tuning radio is a ……… of sound.
Oasis School Science and Technology -5 205 c. The sound that produces unpleasant effect is called …… d. A large temple bell produces a …… sound than a small one. e. The disturbance in a medium is called ……… 3. Tick (√ ) the correct statements and cross (×) the incorrect ones. a. All vibrating bodies produce sound. b. The sound produced by the harmonium is called musical sound. c. The sound produced by a girl is low-pitched. d. Sound cannot travel through water. e. The speed of sound is maximum in gases and least in solids. 4. Answer the following questions in very short. a. What does sound needs for propagation? b. What is the wave in the liquid called? c. What produces musical sound? d. Between the boys and girls, who do you think has sound with high pitch? e. Whose sound is loud; a young girl or an adult girl? 5. Give reasons. a. Astronauts need devices to talk to each other in outer space. b. During lightning we see the spark first and listen the sound afterwards. c. All musical sound cannot be pleasant to all people. d. We listen sound faster in solids than from the air. 6. Differentiate between: a. Pitch of sound and Loudness of sound b. Sound in solid and gaseous medium
206 Oasis School Science and Technology -5 7. Answer the following questions in short. a. What is sound? How is it produced? b. What is meant by a source of sound? Name any three sources of sound. c. What is a musical sound? Name any two equipment that produce a musical sound. d. What is noise? Name any two sources of noise. e. What do you mean by the pitch of sound? f. What is loudness of sound? Name any three factors that affect the loudness of sound. g. What is wave motion? Name the two types of waves. h. What is the speed of sound in air and water? 8. Answer the following questions. a. List down the factors on which does the loundness of the sound depend? b. Why do you think sound cannot propagate through vacuum? c. Explain an activity to show that sound propagates through liquid medium. 9. What could be the conclusion of the following experiments. a. b. c. Hi ! Hello ! Thread Bucket Bell Hammer Water
Oasis School Science and Technology -5 207 UNIT 7.3 ELECTRICITY Estimated teaching periods Theory 6 Practical 3 Introduction and construction of electric circuit Functions of wire, cell, bulb and switch in electric circuit Safety precautions while using electricity The Sequence of Curriculum Issued by CDC Michael Faraday was an English physicist and chemist. He was born in 1791 and died in 1867 in England. He conducted many experiments contributed greatly to the understanding of electromagnetism. He was the inventor of electrical generator. His electrical generator converted magnetic energy into electrical energy. The generator that is used in producing electrical energy in hydropower plants are developed on the foundation of Faradays invention. About the Scientist Michael Faraday Key terms and terminologies 1. Simple Cell : A simple cell is a device which consists of two metal plates of copper and zinc immersed in dilute sulphuric acid. 2. Photo Cell : The cell which converts solar energy into electrical energy is called photo cell. 3. Dynamo : Dynamo is a device which converts mechanical energy into electrical energy. 4. Generator : The generator is a very big dynamo which produces a large amount of electricity. 5. Electric Circuit : An electric circuit is a path made by connecting a cell, a conducting wire and a bulb. 6. Open Circuit : When the switch is turned to 'OFF' position, the bulb does not glow. Such electric circuit is called open circuit.
208 Oasis School Science and Technology -5 7. Closed circuit : When the switch is turned to 'ON' position, the bulb glows. Such electric circuit is called closed circuit. 8. Conductors : The substances through which electricity can flow easily are called conductors. 9. Insulators : The substances through which electricity cannot flow at all are called insulators. 10. Semiconductors : The substances which allow only a part of current to pass through them are called semiconductors. Introduction Electricity is the most common and useful form of energy. It is produced due to continuous flow of electrons through a conductor or flow of charges. It is used at our homes for lighting, heating, running fans, etc. It is used for operating computer, television, radio, cassette player, etc. Electricity is also used in industries and factories to run various machines. Sources of Electricity In the modern world, we use a large number of electronic appliances such as computer, television, radio, camera, washing machine, refrigerator, calculator, watch, etc. Electrical energy is required to operate these appliances. Similarly, electrical energy is essential to run industries, to operate fans, to obtain light and heat, etc. The devices from which we obtain electricity are called sources of electricity. The three major sources of electricity are as follows: 1. Cell 2. Photo cell or Solar cell 3. Dynamo and Generator 1. Cell A cell is the source of direct current. It converts chemical energy into electrical energy. There are two types of cells. They are primary cell and secondary cell. In this unit, we will discuss two types of primary cell, viz. Simple cell and Dry cell.
Oasis School Science and Technology -5 209 a. Simple cell A simple cell consists of two metal plates namely zinc and copper. These metal plates are immersed in a glass vessel containing dilute sulphuric acid. A simple cell is a device which consists of two metal plates of copper and zinc immersed in dilute sulphuric acid. The structure of a simple cell is shown below: Fig: Simple cell In a simple cell, when copper plate and zinc plate are connected by a copper wire, electrons flow continuously. As a result, electricity is produced. So we can light a bulb by using a simple cell. A simple cell contains a liquid, i.e. dilute sulphuric acid. So it cannot be transported easily and therefore it is not widely used. b. Dry cell Dry cell is a modified simple cell in which a paste of ammonium chloride is used instead of dilute sulphuric acid. No liquid is used in this cell. So, this cell is called dry cell. The structure of a dry cell is shown in the following figures. Brass cap(+) Seal Carbon rod Zinc container Muslin bag Manganese dioxide and activated carbon Paste of ammonium chloride Negative terminal Fig: Dry cell Fig: Internal structure of a dry cell A dry cell consists of a paste of ammonium chloride in a zinc Copper plate Dilute sulphuric acid Beaker Switch Copper wire Zinc plate
210 Oasis School Science and Technology -5 container with a leakproof cover. There is a carbon rod in the middle which is surrounded by a muslin bag filled with a mixture of manganese dioxide and carbon powder. The carbon rod contains a brass cap at the top. Dry cells are cheap and portable. So, they are widely used in torchlight, radio, clock, camera, toys, walk-man, etc. 2. Photo cell The cell which converts solar energy into electrical energy is called photo cell. It is also called solar cell. A single photo cell cannot produce a large amount of electricity. So numerous photo cells are connected in solar panels. Have you seen a solar panel? A solar panel produces enough electrical energy to light bulbs, to heat water or to pump out water through a well. In our country, solar energy is used in remote areas as a source of electricity. Fig: Photo cell Fig: Solar panel 3. Dynamo and Generator Have you seen a dynamo of a bicycle? When the wheel of a bicycle is rotated, the dynamo produces electricity. This electricity lights the bulb. Dynamo is a device which converts mechanical energy into electrical energy. A small amount of electricity is produced by a dynamo. The generator is a very big dynamo which produces a large amount of electricity. In hydroelectric stations, turbines are rotated with the help of the running water to produce hydroelectricity. Fig: Bicycle dynamo Fig: Generator
Oasis School Science and Technology -5 211 Electric Circuit An electric circuit is a path made by connecting a cell, a conducting wire and a bulb. It is a continuous path along which current flows. The things required for Dry cell making an electric circuit are described below: a. Cell or Battery: It acts as the source of electricity. b. Conducting wire: It is the medium through which electric current flows. c. Bulb: A bulb is a device which converts electrical energy into heat energy and light energy. d. Switch: It is a device which is used to open or close an electric circuit. Open circuit and Closed circuit When the switch is turned to 'OFF' position, the bulb does not glow. Such electric circuit is called open circuit. In such condition, the current cannot flow continuously through the wire. So, the bulb does not glow. When the switch is turned to 'ON' position, the bulb glows. Such electric circuit is called closed circuit. In such condition, electricity flows continuously through the circuit. As a result, the bulb glows. In our home, school or office, electric circuits are closed to light the bulbs or operate other appliances. Electric circuits are closed or opened with the help of switches fixed on the switch boards. Dry cell Copper wire Switch off Bulb glowing Fig: Open circuit Dry cell Copper wire Bulb Switch on Fig: Closed circuit
212 Oasis School Science and Technology -5 Activity 1 • Take a dry cell, three pieces of copper wire, a bulb with holder and a switch. Connect them as shown in the figure below: Dry cell Copper wire Switch off Bulb Dry cell Copper wire Switch on Bulb glowing Fig: Open circuit Fig: Closed circuit • Now, turn the switch to "ON" position. Does the bulb glow? • Turn the switch to "OFF" position and observe the bulb. • What can you conclude from this activity? When the switch is turned "ON", electricity flow continuously, so the bulb glows. But electricity cannot flow continuously when the switch is turned 'OFF', so the bulb does not glow. Conductors, Insulators and Semiconductors When we connect a bulb with a dry cell through a copper wire, the bulb glows. But the bulb does not glow if we use plastic instead of the copper wire. It is because electricity flows through the copper wire but not through the plastic. The substances through which electricity can flow easily are called conductors. Most of the metals like copper, aluminium, gold, silver, iron, etc. are conductors. The substances through which electricity cannot flow at all are called insulators. Wood, plastic, rubber, paper, air, etc. are insulators. The substances which allow only a part of current to pass through them are called semiconductors. For example, lead, silicon, etc. Fact File Gold and silver are the better conductors than copper wire but they are expensive for us to offer. So copper wires are used in household wiring.
Oasis School Science and Technology -5 213 Activity 2 • Bring a dry cell, three pieces of copper wire, a bulb, a bulb holder and connect them as shown in the figure. Leave a gap PQ between two pieces of the wire. • Collect some small pieces of various objects such as aluminium wire, a piece of wood, rubber, blade, pencil, cork, iron, coin, etc. • Now, place each and every piece one by one to fill the gap between P and Q. What do you observe? Does the bulb glow or not? On the basis of your observation, fill in the blanks in the given table. S. No. Object Bulb glows Bulb does not glow Conductor Semiconductor Insulator Bright Dim 1. Copper wire × × × × 2. ......... ......... ......... ......... ......... ......... ......... 3. ......... ......... ......... ......... ......... ......... ......... 4. Lead × × 5. 6. 7. 8. • What can you conclude from this experiment? Switch Dry cell Bulb glowing Copper Wire Dry cell Copper wire P Q Bulb Fig: Identifying conductors, semiconductors and insulators Fig: Electric circuit
214 Oasis School Science and Technology -5 Project Work • Collect potato, lemon, orange, apple, etc. Insert a plate of zinc and a plate of copper in each of them one by one. • Connect those plates with the Galvanometer as shown in the given figure. • Does the needle of the galvanometer show deflection? Observe carefully. • Write down the conclusion of this activity. Reasonable Thinking Skill Reasonable Thinking Skill R T S 1. Which of the following converts mechanical energy into electricity? a. Dynamo b. Dry Cell c. Photo cell d. Bulb Answer: a 2. Which of the following statement about electricity is true. a. Bulb glows at open circuit. b. Bulb glows at closed circuit. c. Generator rotates turbines to produce electricity. d. Copper wire does not conducts electricity. Answer: Bulb glows at closed circuit. 3. Define a dry cell. A cell is a dry cell that consists of a paste of ammonium chloride in a zinc container with a leakproof cover.
Oasis School Science and Technology -5 215 4. Why is lead known as a semiconductor? Lead is known as a semiconductor because it allows only a part of current to pass through it. 5. How are conductors different from insulators? The differences of conductors from insulators are given below. Conductors Insulators a. They pass electricity through them. a. They cannot pass electricity through them. b. Examples are copper, silver, gold, iron etc. b. Examples are rubber, plastic, wood etc. Exercises 1. Choose the best answer from the given alternatives. a. Which of the following is a source of electricity? i. Bulb ii. Battery iii. Copper wire iv. Switch b. Which of the following equipment converts light into electricity? i. Photo cell ii. Dry cell iii. Dynamo iv. Generator c. Which equipment is used to generate electricity by using water? i. Dry cell ii. Turbine iii. Simple cell iv. Bulb d. Which of the following is a conductor of electricity? i. Copper wire ii. Plastic iii. Wood iv. Stone e. The substance that does not allow current to pass through it is called i. Insulator ii. Conductor iii. Semi-conductor iv. None of the above
216 Oasis School Science and Technology -5 2. Fill in the blanks using appropriate words. a. Dry cell, dynamo and generator are the ……......… of electricity. b. ….........… is produced due to the continuous flow of electrons. c. Photo cell converts …...........…… energy into ……......... energy. d. The electricity generated by rotating turbine with the help of water is called …...................… e. The equipment that produces electricity in a large scale is called …....… f. The substance that allows only a part of current to pass through it is called …….............… 3. Tick ( √ ) the correct statements and cross (×) the incorrect one. a. Electricity is produced due to the continuous flow of electrons. b. Copper wire and bulb are the sources of electricity. c. The path through which electric current flows is called an electric circuit. d. Electricity cannot pass through conductors. e. Lead and silicon are semiconductors. 4. Answer the following questions in very short. a. Which device converts mechanical energy into electrical energy? b. Which cell contains the paste of ammonium chloride with leaked proof covering? c. Which conductor is used in household electrification? d. What type of cell converts solar energy to electrical energy? e. Which circuit; open or close glows bulb? 5. Give reasons. a. Dynamo is used in bicycles. b. Copper is used in household wiring for electricity. c. Rubber is known as insulators. d. Open circuit does not glow bulb.
Oasis School Science and Technology -5 217 6. Differentiate between: a. Dynamo and Generator b. Conductor and Insulator c. Open circuit and Closed circuit d. Semiconductor and Insulator 7. Give short answers to the following questions. a. What is electricity? Write any two uses of electricity. b. What are sources of electricity? Write any three sources of electricity. c. What is photo cell? Write down its function. d. What is a simple cell? Draw a neat and labelled figure of a simple cell. e. What is a dynamo? How does it differ from a generator? f. What is hydroelectricity? g. What is an electric circuit? h. What are conductors? Give any two examples. i. What are insulators? Give any two examples. j. What are semiconductors? Give any two examples. 8. Identify the given devices or objects and write down their utilities. a. b. c. 9. Answer the following questions. a. How is electricity produced in hydroper plant? Describe in brief. b. How does dynamo works? Explain. 9. Draw a neat schematic diagram of open and closed circuit.
218 Oasis School Science and Technology -5 THE EARTH AND SPACE
Oasis School Science and Technology -5 219 Key terms and terminologies 1. Solar System : The family of the sun which consists of eight planets and their satellites, comets, etc. is called solar system. 2. Satellites : Satellites are the the heavenly bodies that revolve around the planets. 3. Comet : A comet is a mass of ice and dust which looks like a bright star with a tail. 4. Elliptical : The object having oval shaped is called elliptical. 5. Orbit : It is a curved path followed by a planet or satellite during revolution. UNIT 8 THE EARTH AND SPACE Estimated teaching periods Theory 16 Practical 4 Sun, earth, moon and other heavenly bodies Revolution of earth and its effect Revolution of moon Phases of moon The Sequence of Curriculum Issued by CDC Nicolaus Copernicus was a Polish astronomer. He was born in 1473 and died in 1543 in Poland. He proposed that the planets have the sun as the fixed point to which their motion are referred. He also proposed that earth revolves round the sun and rotates once daily on its own axis. Due to this contribution in astronomy, he is known as the father of the solar system. About the Scientist Nicolaus Copernicus
220 Oasis School Science and Technology -5 6. Planets : Planets are the heavenly bodies that revolve around the sun. 7. Twinkle : To shine with a light that keeps changing from bright to faint to bright again. 8. Waxing : The gradual increase in the bright disc of the moon is called waxing of the moon. 9. Waning : The gradual decrease in the bright disc of the moon is called waning of the moon. 10. Lunar : Description of any object related to the moon. Introduction The sun is a medium-sized star closest to the earth. It is a huge ball of burning gases. The sun is extremely hot. It releases a large amount of heat and light energy. We obtain heat and light from the sun. What would happen if there were no sun? Have you ever wondered? All the plants and animals including human beings get heat and light energy from the sun. Green plants need sunlight for photosynthesis. The heat of the sun maintains water cycle on the earth. The sun is the ultimate source of energy. The heat of the sun keeps the earth warm. Therefore, all plants and animals would die in absence of the sun. Solar system Fig: Solar system
Oasis School Science and Technology -5 221 The family of the sun which consists of eight planets and their satellites, comets, etc. is called solar system. The sun remains at the centre of the solar system. All the members of the solar system revolve around the sun. Planets We know that the earth is a planet. It revolves around the sun in an elliptical orbit. Planets do not have their own source of light. However, they appear bright in the sky. The planets shine and become visible because they reflect the sunlight that falls on them. The sun holds all the planets together with its strong force of attraction. Each planet moves around the sun in its own elliptical orbit. Planets are the heavenly bodies that revolve around the sun. The eight planets of the solar system in the order of increasing distance from the sun are given below: i. Mercury ii. Venus iii. Earth iv. Mars v. Jupiter vi. Saturn vii. Uranus viii. Neptune Mercury Mercury is the smallest planet of the solar system. It is closest to the sun. The part of mercury that faces the sun is extremely hot and the other part is extremely cold. Mercury has no atmosphere, hence life cannot exist there. Venus Venus is the brightest and hottest planet of the solar system. It is the closest planet to the earth. The atmosphere of the Venus mainly consists of carbon dioxide. Life cannot exist on the venus. Mercury Venus Fact File The atmosphere of Venus is rich in carbon-dioxide that absorbs heat. So it is the hottest planet in the solar system.
222 Oasis School Science and Technology -5 Activity 1 • Mercury can be seen just before the sunrise in the months of September and October. Similarly, it can be seen just after the sunset in March and April. Observe mercury and show it to your family members also. • Venus can be seen just before the sunrise and just after the sunset. Observe venus and show it to others also. Please note that venus is the brightest heavenly body in the night sky after the moon. Earth The earth is the third nearest planet from the sun in which we live. This planet has life supporting gases, i.e. oxygen and carbon dioxide, water and suitable temperature for living beings. Therefore, life exists on the surface of the earth. The earth has one natural satellite, i.e. the moon. The earth is the only planet which has all the requirements for the existence of life. The earth takes 365.25 days to complete one revolution around the sun. It takes 24 hours to complete one rotation in its own axis. It causes day and night to occur on the earth. Mars Mars is the fourth distant planet from the sun. It can be seen with our naked eyes. It looks like a bright orange-red star. It is almost half the size of the earth. The atmosphere of the mars mainly consists of nitrogen gas. The mars has two moons. Jupiter Jupiter is the largest planet of the solar system. It is the third brightest object in the night sky after the moon and the Venus. The Jupiter looks like a bright star with our naked eyes. It consists of bands of clouds and a big red spot. This planet has four large moons and 59 small moons. Earth Mars Jupiter
Oasis School Science and Technology -5 223 Saturn Saturn is the second largest planet and the third farthest planet of the solar system. This planet is surrounded by rings of dust and rocks. The Saturn has 60 moons. Uranus Uranus is the second farthest planet of the solar system. It is a very cold planet. Uranus too has rings around it. This planet has 27 moons. Neptune Neptune is the farthest planet of the solar system. It cannot be seen with our naked eyes. It is the coldest planet. It has 13 moons. Activity 2 • Make a colourful chart of the solar system with the help of your textbook or your teacher. • Name the eight planets of the solar system. Also, write any two features of each planet in your exercise book. Dwarf Planets Some heavenly bodies look round like planets and are not the moons of other planets. They also orbit the sun but that does not lie on the same plane like other Saturn Uranus Neptune Fig: Dwarf planets
224 Oasis School Science and Technology -5 planets. Such bodies are called dwarf planets. Pluto, Eris, Makemake etc. are dwarf planets. Except Ceres, other dwarf planets orbit sun from the very edge of solar system. Asteroids Beside planets, our solar system contains small body of rocks containing iron orbiting the sun. They are called asteroids. Asteroids are the heavenly bodies found between the orbits of Mars and Jupiter. Meteoroids The lump of rocks and iron which are smaller than asteroids and are found orbiting round the sun are called meteoroids. They are found scattered over the solar system. When a meteoroid enters into the atmosphere of the earth, it burns up and we can see it as a stripe of light. Meteoroids burning in the atmosphere of the earth are called meteors. If the meteoroid does not burn completely in the atmosphere and reaches to the surface of the earth, it is called meteorite. Fig: Asteroids Fig: A meteoroid in earth atmosphere Stars When we look at a dark and clear night sky, we can observe numerous twinkling objects. Those objects are called stars. The extremely hot Stars.
Oasis School Science and Technology -5 225 balls of gases that twinkle at night are called stars. Planets do not twinkle but stars do. Stars have their own source of light but planets only reflect the light obtained from the sun. Some of the stars that we see in the sky are a thousand times larger than the sun, whereas some stars are smaller than the sun. At a glance, stars appear like very small shiny points. Stars appear very small since they are very far from the earth. Actually, stars are extremely large burning balls of gases. Stars are luminous bodies like the sun. The sun is also a medium-sized star. The sun appears very bright and large in comparison to the other stars. It is because the sun is the star nearest to the earth. Planets are extremely small in size as compared to the size of the sun or stars. Satellites The heavenly bodies that revolve around planets are called satellites. For example, the moon is the natural satellite of the earth. All the planets of the solar system have satellites except Mercury and Venus. Human have sent man-made satellites in the space. It supports communication and provides new information to the earth. Comet The coma shaped heavenly bodies made up of ice, rock and metals which revolve round the sun in an elliptical orbit are called comets. For example encke, halley, shoemaker levy, etc. Activity 3 • Observe various types of heavenly bodies in the clear night sky. Try to differentiate between stars and planets. • Prepare a short report on the basis of your observation and show it to your teacher. Moon
226 Oasis School Science and Technology -5 Moon The moon is the natural satellite of the earth. It is the brightest object that appears in the clear night sky. The moon is about one-fourth of the size of the earth. The surface of the moon has many craters, dark patches and mountains. The moon does not have water and atmosphere. So, life cannot exit on the moon. Activity 4 • Starting from the full moon or new moon, observe different shapes of the moon every day. • Draw the diagram of the shapes of the moon that you observe. Also record the time of the rising of the moon every day. Motion of the earth The earth is not a perfect sphere. It is bulging at the equator and somewhat flat at the poles. The earth has two types of motions, viz. revolution and rotation. The motion of the earth around the sun is called revolution. The earth revolves around the sun at a distance of 15 crore kilometres (approx.) in an elliptical orbit. The earth takes 365.25 days (1 year) to complete one revolution around the sun which is called annual motion or orbital motion (revolution). The earth spins about its own imaginary axis like a top, from west to east. The imaginary line passing through the north and south pole of the earth is called axis. The earth completes one rotation about its own axis in 24 hours (1 day). This motion of the earth is called diurnal motion (rotation). Fig: Earth revolves around the sun
Oasis School Science and Technology -5 227 Occurrence of Day and Night on the Earth The sun gives heat and light all the time. However, only half of the earth faces the sun due to spherical shape of the earth, whereas the other half is opposite to the sun. The half of the earth which receives the sunlight has day and the half opposite to the sun has night. As the earth steadily moves about its own axis, gradually the part of the earth having day moves away from the sun, i.e. towards night side and viceversa. In this way, days and nights occur on the earth. Effects of Rotation and Revolution of the Earth The axis of rotation of the earth is tilted at an angle of 66.5° with its orbital plane. It has following effects on the earth. i. Days and nights are not equal except in the equatorial region. Some days are longer than nights and some nights are longer than days. ii. Change of seasons takes place. iii. The rays of the sun do not fall perpendicularly in a place all the time. It affects the climate of that place. iv. The sunrise and sunset do not always take place from the same place. v. The height of the sun from the earth in the afternoon changes every day. Change of Seasons The earth revolves around the sun in an elliptical orbit. The earth completes one revolution in 365 days. The axis of rotation of the earth is tilted at an angle of 66.5° and the earth is not always at the same distance from the sun due to its elliptical orbit. Due to these reasons, change of seasons takes place on the earth. The duration of one year is divided into four seasons. They are as follows:
228 Oasis School Science and Technology -5 i. Summer season ii. Autumn season iii. Winter season iv. Spring season The tilted axis of rotation of the earth always lies in the same direction. Due to this tilt in the axis of rotation, the position of the northern and southern hemispheres of the earth toward the sun keeps changing throughout the year. Northern spring Southern fall Northern summer 21 March equinox Northern winter A 21 June solstice Southern winter B Southern summer Northern fall Southern spring C 22 December solstice 23 September equinox Fig: Earth's orbit around the sun When the northern hemisphere is tilted towards the sun, we experience summer, whereas the people in the southern hemisphere experience winter. Similarly, autumn and spring occur when the earth lies in between these two extreme positions in its orbit. Due to change in the length of days, the amount of heat and light received by the earth changes every day. This in turn gives rise to four seasons, viz. summer, autumn, winter and spring. Reasonable Facts Change of seasons takes place on the earth. The axis of rotation of the earth is titled at an angle of 66.5° and the earth is not always at the same distance from the sun due to its elliptical orbit. Due to these reasons, change of seasons takes place on the earth.
Oasis School Science and Technology -5 229 Phases of the Moon The moon is the natural satellite of the earth. It is the brightest object in the clear night sky. The moon is a non-luminous body. It has no light of its own. It only reflects the light of the sun. The moon always presents its same face towards the earth. When the reflected light of the moon reaches the earth, we see the moon. Only that part of the moon which reflects the sunlight towards the earth is visible. When the moon lies in between the sun and the earth, the reflected light from the moon does not reach the earth and hence the moon is not visible. This day is called new moon day. On new moon day, the dark side of the moon faces the earth. On the night just after the new moon day, crescent moon is seen. The rest of the moon is only faintly visible. The crescent goes on increasing every day till the 15th day from the new moon day when the full bright face of the moon is visible. This day is called full moon day. When the earth lies between the moon and the sun, the full bright face of the moon is seen from the earth. This day is called full moon day. The gradual increase in the bright disc of the moon is called waxing of the moon. The bright disc of the moon increases for 15 days after the new moon day. This duration is called bright half. After the full moon, the bright face of the moon goes on decreasing every night for 15 days. This duration is called dark half. The gradual decrease in the bright disc of the moon is called waning of the moon. The waxing and waning of the disc of the moon, as the moon revolves Fig: Phases of the moon
230 Oasis School Science and Technology -5 around the earth, is called phases of the moon. On full moon day, the moon rises in the eastern sky when the sun sets in the western sky and the moon rises after 50 minutes in the following day. The moon revolves around the earth in its own orbit. The moon completes one revolution around the earth in 27 1 3 days. This duration is called sidereal month. Similarly, the duration between two consecutive full moons or new moons is 29 1 2 days. This duration is called synodic month. However, as the moon revolves around the earth, the earth moves ahead in its own orbit around the sun. Thus, from the earth, the moon appears to complete one revolution between one new moon to next new moon in 29.5 days. Project Work • Observe the shape of the moon for one month. Draw a chart showing the phases of the moon and submit to your science teacher. Activity 5 1. Starting from the full moon or new moon, observe different shapes of the moon every day. 2. Draw the diagram of the shapes of the moon that you observe. Also record the time of the rising of the moon every day. Differences between New moon and Full moon New moon Full moon 1. When the moon lies between the sun and the earth, the reflected light from the moon does not reach the earth and hence the moon is not visible. This phase of moon is called new moon. 1. When the earth lies between the moon and the sun, the full bright face of the moon is seen from the earth. This phase of moon is called full moon. 2. Night of new moon is dark. 2. Night of full moon is bright.
Oasis School Science and Technology -5 231 Difference between Bright half and Dark half Bright half Dark half 1. The bright disc of the moon increases for 15 days after the new moon day. This duration is called bright half. 1. After the full moon, the bright face of the moon goes on decreasing every night for 15 days. This duration is called dark half. 2. Nights are bright 1. Nights are dark. Differences between Synodic month and Sidereal month Synodic month Sidereal month 1. It is the duration between two consecutive full moons or new moons. 1. It is the duration that moon completes one revolution around the earth. 2. Its duration is 29.5 days. 2. Its duration is 27 days, 7 hours, 43 minutes and 11 seconds. Reasonable Facts Days and nights are not equal on all the places of the earth. The axis of rotation of the earth is titled at an angle of 66.5° with its orbital plane. So, days and nights are not equal on all the places of the earth. Reasonable Facts Day and night are equal in all parts of the earth on September 23 and March 21. On march 21 and on September 23, the rays of sun fall perpendicularly on the equator. So, days and nights are equal in all parts of the earth.
232 Oasis School Science and Technology -5 Reasonable Thinking Skill Reasonable Thinking Skill R T S 1. What is the duration for two consecutive full moon night? a. 27.5 days b. 28.5 days c. 29.5 Days d. 30 days Answer: The duration for two consecutive full moon nights is 29.5 Days. 2. Which is the hottest planet in the solar system? Venus is the hottest planet in the solar system. 3. Which of the following statements are true. a. Uranus has no any moons. b. Change in the amount of solar energy received by the earth causes change in season. c. Nights are dark in dark half. d. Mars is a red planet. Answer: The options b, c and d are true. 4. Define satellites. What is the natural satellite of the planet called? Satellites are the natural or man-made bodies that revolve round the planet. Natural satellite of the planet is called moon. 5. Mercury is nearest to the sun but the Venus is hottest planet. Why? The atmosphere of Venus is rich in carbon-dioxide gas. This gas traps solar energy. So, Venus is the hottest planet in the solar system. 6. List any three major differences between planets and stars Three major differences between the planets and stars are: Planets Stars a. They cannot produce their own heat and light. a. They can produce their own heat and light.
Oasis School Science and Technology -5 233 b. There are only eight planets in the solar system. b. There are countless stars in the universe. c. Distance between the planets changes over time. c. Distance between the stars do not change over time. Exercises 1. Select the best answer from the given alternatives. a. We obtain heat and light from the ........... i. sun. ii. moon. iii. stars. iv. all of the above. b. The heavenly bodies that revolve around the sun are called ........... i. stars. ii. satellites. iii. planets. iv. none of the above. c. The atmosphere on the mars consists of ........... i. oxygen gas. ii. nitrogen gas. iii. hydrogen gas. iv. carbon dioxide. d. The farthest planet of the solar system is ........... i. jupiter. ii. neptune. iii. pluto. iv. saturn. e. The bright portion of the moon goes on increasing in ....... i. full moon. ii. new moon. iii. bright half. iv. dark half. 2. Fill in the blanks with appropriate words. a. The largest planet of the solar system is ................. b. Stars have their own source of ................. c. The heavenly bodies that revolve around the planets are ................. d. The surface of the moon has many .................
234 Oasis School Science and Technology -5 e. The earth takes ................. days to complete one revolution around the sun. f. In a new moon day, the ...... lies in between the ................. and the sun. 3. State whether the following statements are True or False. a. The sun is the nearest star from the earth. (...) b. There are nine planets in the solar system. (...) c. Planets do not have their own source of light. (...) d. Venus is the smallest planet. (...) e. Earth is the natural satellite of the moon. (...) f. The moon is the brightest object in the night sky. (...) 4. Answers the following question in very short. a. Which planet is also called red planet? b. In which half of the moon the nights are bright? c. What is the natural satellite of the planet called? d. What cause change in day and night? e. Which factor cause change in seasons? f. What is the name of the path on which planets revolve around the sun? 5. Match the following: A B i. Mercury ( ) Hottest planet ii. Star ( ) Largest planet iii. Jupiter ( ) Moon iv. New moon ( ) Bright night v. Satellite ( ) Sun vi. Full moon ( ) Smallest planet ( ) Dark night
Oasis School Science and Technology -5 235 6. Give reasons: a. The sun is called a star. b. Saturn is called a planet. c. Mars is also known as red planet. d. Earth is only living planet. e. Moon is called a satellite. f. The face of the moon goes on changing. 7. Differentiate between: a. Planets and Stars b. Mercury and Neptune c. Planet and Satellite d. Full moon and New moon 8. Answer the following questions in short: a. Write any three features of the sun. b. Define solar system? c. What are planets? Name eight planets of the solar system in order nearest from the sun. d. Name the hottest and the coldest planets of the solar system. e. What are stars? Write any two features of stars. f. What are satellites? Name the planets that do not have satellites. g. What is meant by phases of the moon? Name major phases of the moon. h. What do you mean by bright-half and dark half ? i. What do you mean by axis of rotation? j. Define sidereal and synodic month.
236 Oasis School Science and Technology -5 9. Identify the following heavenly bodies and write any two features of each. i. ii. iii. 10. Answer the following questions. a. Discuss what major factors make the earth a living planet. b. Explain how season changes in the earth. c. Is it possible to have other solar systems of other stars? If yes, put down your logics? d. Describe the phases of moon. 11. Draw a neat figure showing the solar system and name all the planets. l2. Draw four main phases of the moon with label.