Magnets - Science and Technology Chapter 8 PDF

FOR ONLINE USE ONLY DO NOT DUPLICATE Chapter Eight Magnets LY...

FOR ONLINE USE ONLY DO NOT DUPLICATE Chapter Eight Magnets LY Introduction In this chapter, you will learn about the meaning of the word magnet, the poles of a magnet, different shapes of magnets and magnetic N force. You will also learn about the uses of magnets in daily life. O The concept of magnet SE Activity 1: Exploring the ability of a magnet to attract objects Materials: A u-shaped magnet, small stones, paper clips, wooden U or plastic pegs, pieces of paper, beverage bottle caps, water bottle caps, a pen, a pencil, pieces of wood, a pin, a razor blade and safety pins E Procedure N 1. Collect all the materials listed above and put them on the table, as LI shown in Figure 1. N 2. Take the magnet and touch it to each of the objects you have collected. O R FO 123 SCIENCE AND TECHNOLOGY STD V.indd 123 7/30/21 11:03 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE LY N O SE Figure 1: The magnet attracts objects 3. Write the names of the objects that the magnet attracted and the U names of the objects that were not attracted in Table 1. Table 1: Objects attracted by the magnet and those that were not E attracted by the magnet Objects attracted by the Objects not attracted by the N magnet magnet LI 1. 1. 2. 2. N 3. 3. O 4. 4. A magnet is an object that attracts iron and other magnetic materials R by using its magnetic force. Examples of objects that are attracted by FO magnets are metals like nails, pins, razor blades and pairs of scissors. Examples of objects that are not attracted by magnets are non-metal objects like wood, plastic and paper. 124 SCIENCE AND TECHNOLOGY STD V.indd 124 7/30/21 11:03 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE Activity 2: Observing the behaviour of magnetic poles Materials: Two bar magnets and a table Procedure 1. Put one magnet on the table. 2. Take the other magnet and place its N pole close to the N pole of the LY first magnet on the table. What do you observe? 3. Place again the N pole of the magnet in your hand near the S pole of the first magnet on the table. What do you observe? N The magnet has two poles: North Pole N and South Pole S. Like poles O of magnets, for example N-N or S-S, repel each other. Unlike poles of magnets, for example N-S, attract each other. SE U S N E Figure 2: Magnetic poles N LI The law of magnets N Like poles of magnets repel each other and unlike poles of magnets attract each other. O Shapes of magnets R As shown in Figure 3, magnets are of various shapes. There are bar FO magnets, horse-shoe magnets, cylindrical magnets, u-shaped magnets and ring magnets which do not have poles. 125 SCIENCE AND TECHNOLOGY STD V.indd 125 7/30/21 11:03 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE N S N S Cylindrical magnet Horse-shoe magnet N LY S N S Bar magnet U-shaped magnet N N O S SE Ring magnet Figure 3: Shapes of magnets U Properties of magnets Activity 3: Observing the properties of magnets E Materials: A bar magnet and a thread N Procedure LI 1. Tie the thread on the magnet and then suspend that magnet in the air, as shown in Figure 4. N O Thread R S N FO Magnet Figure 4: Suspending a magnet in the air 126 SCIENCE AND TECHNOLOGY STD V.indd 126 7/30/21 11:03 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE 2. Wait until the magnet is settled. In which direction of the earth does the N pole of the magnet point? 3. Push one pole of the magnet to make it rotate. Wait until it is settled again. In which direction do the N pole and S pole point? When a bar magnet is suspended in the air, its N pole will point to the N pole of the earth and the S pole of a magnet points to the S pole of the earth. This is because the North pole of a magnet is a North seeking pole and the South pole is a South seeking pole. LY Magnetic Force N Activity 4 (a): Demonstrating the existence of magnetic lines of O force Materials: Iron filings, white paper, a bar magnet and a table Procedure SE 1. Spread the iron filings on the white paper on top of the table. U 2. Put the paper with iron filings on top of the bar magnet. 3. Gently shake the paper. 4. Observe how the iron filings are aligned and compare them with the E pattern shown in Figure 5. N LI S N N O Figure 5: Magnetic lines of force The iron filings will concentrate on the magnet’s poles. The central part R of the magnet will have a different pattern from the patterns formed near the poles. The lines of the iron filings represent the magnetic lines of FO force that start at the N pole and end at the S pole of the magnet. The concentration of magnetic lines of force is greater at the poles than at any other parts of the magnet. 127 SCIENCE AND TECHNOLOGY STD V.indd 127 7/30/21 11:03 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE Activity 4 (b): Exploring the pattern of magnetic force between like poles of magnets which have been placed close to each other Materials: Two bar magnets, white paper, iron filings and a table Procedure 1. Spread the iron filings on the paper. 2. Put the two magnets on the table. Make sure the two like poles are LY facing each other at a close distance. 3. Put the paper with iron filings on the top of both magnets. N 4. Move one magnet towards the other. What do you see? O 5. Draw in your exercise book the patterns you have seen. SE U S N N S E N Figure 6: Magnetic forces between like poles of magnets LI The concentration of iron filings is lowest between the adjacent like poles of the magnets, as shown in Figure 6. This shows that the forces N between the two like poles of magnets repel each other. O R FO 128 SCIENCE AND TECHNOLOGY STD V.indd 128 7/30/21 11:03 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE Activity 4 (c): Exploring the patterns of magnetic forces between unlike poles of magnets Materials: Two bar magnets, white paper, iron filings and a table Procedure 1. Spread the iron filings on the white paper. 2. Set up the two magnets on the table. Make sure the two unlike poles are facing each other and are separated by a short distance. LY 3. Put the paper with iron filings on top of the magnets. N 4. Move one magnet towards the other. What do you see? 5. Draw the shape you have seen and compare it with the one shown O in Figure 7. SE U S N S N E N LI Figure 7: Magnetic forces between unlike poles of magnets N The concentration of iron filings is greatest between the adjacent unlike poles of the magnets. This shows that the forces between the two unlike O poles of magnets attract each other. R FO 129 SCIENCE AND TECHNOLOGY STD V.indd 129 7/30/21 11:03 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE Activity 4 (d): Investigating the penetration of magnetic force through matters Materials: Water, two empty glasses, two nails, a bar magnet and a table Procedure 1. Put one nail in one empty glass (see Figure 8). 2. Pour some water into the second glass. 3. Put the second nail in the glass containing the water. LY 4. Dip the magnet slowly in the glass containing the water near the nail. What do you see? 5. Pass the magnet outside the glass with no water near the nail. What N do you see? O SE U E N Figure 8: The penetration of magnetic force in matter LI Magnetic force managed to penetrate into the water and pulled the nail in the second glass. Similarly, the magnet attracted the nail through N the empty glass. This shows that magnetic lines of force can penetrate through different matters. O R Exercise 1 Answer the following questions. FO 1. What is a magnet? 2. State the law of magnets. 130 SCIENCE AND TECHNOLOGY STD V.indd 130 7/30/21 11:03 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE 3. Draw the layout of magnetic lines of force for the following situations: (a) Like poles brought close together; and (b) Unlike poles brought close together. 4. Mention the properties of magnets. 5. Sketch four different shapes of magnets. LY Uses of magnets Magnets have several uses. They are used in making devices for lifting objects and in electricity generation. A magnet is used as a tool for N separating metals from non-metals. Also, magnets are used in electric bells and in a magnetic compass. O (a) Lifting heavy objects SE Magnets are used to pick up objects and move them from one place to another. Port cranes use magnets to load or unload objects from ships (see Figure 9). Electronic technicians use magnetized screwdrivers to U pick up small metallic screws. E Crane N LI Magnet Lifted load N Ship O R FO Figure 9: Crane unloading using a magnet 131 SCIENCE AND TECHNOLOGY STD V.indd 131 7/30/21 11:03 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE (b) Electric bell It is a bell that is powered by electricity. Activity 5: Making an electric bell Materials: An electric switch, two dry cells, insulated wire, two pieces of soft iron, a wooden soft board, one large nail, small nails and a hammer Procedure LY 1. Prepare the wooden soft board (see Figure 10(a)). N O SE Figure 10(a): Wooden board 2. Fold the first piece of soft iron, as shown in Figure 10(b). U E N Figure 10(b): The first piece of soft iron LI 3. Fold the second piece of soft iron, as shown in Figure 10(c). N O R FO Figure 10(c): The second piece of soft iron 132 SCIENCE AND TECHNOLOGY STD V.indd 132 7/30/21 11:03 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE 4. Take the insulated wire and wind it around the larger nail in many turns, as in Figure 10(d). LY Figure 10(d): Large nail wound by the insulated wire 5. Hammer the nail wound with the insulated wire coil into the board N (see Figure 10(e)). O SE U Figure 10(e): The board and the nail wound with the insulated wire coil 6. Fix the first piece of soft iron on the board; one edge must be E above the top of the nail without touching it. Fix the second piece N of soft iron on the board; one of its edges should touch the top of the first soft iron. See Figure 10(f). LI First soft iron N O Second soft iron R FO Figure 10(f) The first and second pieces of soft iron mounted on the board 133 SCIENCE AND TECHNOLOGY STD V.indd 133 7/30/21 11:03 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE 7. Connect the switch, wire, dry cells and nail wound with the insulated wire, as shown in Figure 10(g). Soft iron Dry cell Dry cell holder LY Switch N Wire O 8. SE Figure 10(g): Electric bell Use the electric bell that you have made to answer the following questions: U (a) What do you see when you turn on the switch? (b) What causes the bell to ring? E (c) What is the function of the nail wound by the insulated wire N in the electric bell? LI Electric bells use magnetic force to work. When an electric current flows in the circuit, the large nail, which is wound by the coils of insulated N wire, acquires a magnetic property and hence attracts the soft iron. The attracted soft iron touches the nail and produces some sound. When the O soft iron is attracted to the nail, it breaks the flow of the electric current at the junction between it and the second soft iron. Thus, the nail loses R its magnetic property and the soft iron returns to its original position. The circuit is completed again and the flow of the electric current resumes FO its cycle. This cycle repeats as long as the switch is turned on. The end- result is the ringing of the bell. 134 SCIENCE AND TECHNOLOGY STD V.indd 134 7/30/21 11:03 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE (c) The compass The compass is a piece of magnet that shows the North and South poles of the earth. People use it to find the directions of places on earth by using the N-S inclination of the magnetic needle of the compass, as shown in Figure 11. Similarly, captains and pilots use it to go in the right direction. N LY N O (d) Electricity generation SE Figure 11: The compass The magnet is used to generate electricity in electrical generators. When U a coiled wire is rotated where there is a magnet, it generates electricity. The bicycle dynamo shown in Figure 12 is a good example of an electrical generator. When the bicycle wheels rotate fast, the electric current produced E increases and the lamp lights up. When the bicycle wheels rotate slowly, the electric current decreases and the lamp becomes dim. N LI N Rotating ridged nob Wheel O Iron core Magnet Copper coil R To light FO Figure 12: Bicycle dynamo 135 SCIENCE AND TECHNOLOGY STD V.indd 135 7/30/21 11:03 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE (e) Separation of objects Activity 6: Using a magnet to pick up materials containing iron Magnets are used in mineral processing plants. They are used to separate materials containing iron from those that don’t. Materials: Soil, a bar magnet, iron filings and a cardboard Procedure LY 1. Put the soil on the cardboard. 2. Put the iron filings on the cardboard. N 3. Mix the soil with the iron filings. O 4. Pass the magnet above the mixture of the soil and the iron filings. 5. Write the results of your experiment. SE Magnets are used to separate iron materials from non-iron materials. Thus, an optician can remove iron particles from the eyes of a patient. Magnets U are also used in making various devices, including radios, phones, voice recorders and microphones. E Properties of magnets N 1. Magnets attract things made of iron. LI 2. Magnetic force is strongest at the poles. 3. When two magnets are brought close to each other, like poles repel N and unlike poles attract each other. O Storing magnets Magnets become weak, if they are not stored properly. If you want magnets R to maintain their forces, the following must be observed: FO 1. Keep magnets away from things made of iron; 2. Make sure like poles of different magnets are not facing each other; 3. Do not heat magnets; 136 SCIENCE AND TECHNOLOGY STD V.indd 136 7/30/21 11:03 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE 4. Do not keep magnets close to objects with large magnetism or electricity; and 5. Do not hit or hammer magnets. Exercise 2 Answer the following questions. Section A: Answer the following questions. LY 1. Choose the correct answer. (i) The purpose of fixing magnets on the opening edges of a freezer and the doors of some cabinets is __________. N (a) to expel heat O (b) to warm the region inside (c) to make the doors stick properly (d) to remove the iron nature (ii) Magnets attract ______. SE (a) iron U (b) wood (c) glass (d) iron and glass E (iii) When a magnet is suspended in the air ________. N (a) its North pole points towards the geographical North (b) its North pole points towards the geographical South LI (c) the North pole and the South pole lack direction N (d) it rotates all the time (iv) If you drop a razor blade into a drum of water, the best way O to pick up the razor blade is ____________. (a) to dive into the drum R (b) to dip into the drum a magnet tied to a long string FO (c) to drill a hole on the drum (d) to pull the razor blade using an iron rod 137 SCIENCE AND TECHNOLOGY STD V.indd 137 7/30/21 11:03 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE 2. Write TRUE for a correct statement and FALSE for an incorrect statement. (a) Like poles of magnets repel each other. _______ (b) Like poles of magnets attract each other. ______ (c) Unlike poles of magnets attract each other. _______ (d) Unlike poles of magnets repel each other. _______ 3. Match the shapes of the magnets in List A with their corresponding LY names in List B. No. List A No. List B i. N S N a A u-shaped magnet O ii. S N SE b A bar magnet iii. U S N c A ring magnet iv. S N d A horse-shoe magnet E N v. S e A cylindrical magnet LI N N 4. Fill in the blanks. a. _____ is used to generate electricity for bicycle lights. O b. From ships, cargo made of or containing _____ materials is lifted up using a magnet. R c. Magnetic lines of force spread from _____ to _____ poles of a magnet. FO d. The type of wire used when making an electric bell is ______. e. A magnet can lose its magnetic force if it is kept together with ______. 138 SCIENCE AND TECHNOLOGY STD V.indd 138 7/30/21 11:03 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE Section B: Answer the following questions. 5. Explain the uses of magnets. 6. Explain the uses of a compass. 7. Draw a picture of an electric bell. 8. List the characteristics of magnets. 9. If you were given a magnet with unknown poles, what would you LY do to determine the North or South pole? 10. How can you make a magnet lose its magnetic property? N O Vocabulary Compass an instrument with a suspended magnetic needle which SE can move and show direction Dynamo a device with a coil rotating between magnets to generate U electricity. E N LI N O R FO 139 SCIENCE AND TECHNOLOGY STD V.indd 139 7/30/21 11:03 AM