Magnetism PDF

Magnetism Definition: Magnetism: A force that acts at a distance between a magnet and a magnetic material is called magnetism. Poles of a magnet: The two ends of a magnet where the magnetism is the strongest are called the poles of a magnet. The materials that have these properties are called mag...

Magnetism Definition: Magnetism: A force that acts at a distance between a magnet and a magnetic material is called magnetism. Poles of a magnet: The two ends of a magnet where the magnetism is the strongest are called the poles of a magnet. The materials that have these properties are called magnets. There are several types of magnets based on their shape: a) horseshoe magnet b) ring magnet c) cylinder magnet d) bar magnet. History of magnetism: A Greek shepherd named Magnes discovered magnetism. A strange rock was found named magnes lithos, the stone from magnesia showed magnetism at first. Magnes lithos, which is a natural magnet, is known as magnetite. Magnesia is the common name for magnesium oxide. magnetite came to be known as the leading stone or lodestone. Magnetic materials: Substances that can be attracted by magnets and which can themselves be magnetized are called magnetic substances or ferromagnetic substances. Iron, Nickel, Cobalt and their compound are magnetic substances. Nonmagnetic materials: Substances that cannot be attracted by magnets and which themselves cannot be magnetized are called non- magnetic substances. Wood, paper, copper, gold are non-magnetic substances. Temporary magnets: Materials that retain their magnetism only for a short period of time are called temporary magnets. Iron and Mumetal are the example of soft magnetic materials used for making temporary magnet like electromagnet. Permanent magnets: Materials that retain their magnetism permanently or for long time are called permanent magnets. Steel and Alcomax are the example of hard magnetic materials used for making permanent magnet. Electromagnet: A piece of soft magnetic materials like iron bar behaves like a magnet only as long as the wire wound over it carries current. Its magnetism is soon lost when the current in the wire is switched off. A magnet of this type is called an electromagnet. An electromagnet works on the magnetic effect of the current. Properties of a magnet: All magnets have the following properties, 1. They attract objects made of iron steel. 2. When a magnet is suspended freely, it comes to rest in the north—south direction. 3. The greater part of the magnetism in a magnet is concentrated at the two ends of the magnet which are termed as north pole (N) and south pole (S). 4. Like poles of a magnet repel while unlike poles attract. Making a magnet: There are three methods of making a magnet. 1) Single touch method: A piece of any magnetic material say AB is taken and placed on a table. A bar magnet is brought close to the magnetic material AB. One end of the bar magnet say north (N) is stroked against the magnetic materials moving from end A to end B. When the bar magnet reaches to end B, it is lifted and the stroke repeated from end A to end B several times keeping two things in mind: a) the same pole of the bar magnet should be used every time and b) strokes should be in the same direction. By stroking magnetic material with the north pole (N) of the bar magnet, end A becomes the north pole (N) and end B the south pole (S). If we bring the south pole (S) of any bar magnet close to the end A of the magnetic material, it will turn into south pole (S) and end B will turn into north pole (N). [see page 53, fig: 4.3 single touch method from your book] 2) double touch method: The magnetic material to be magnetized, say AB, is placed on a bench and two bar magnets of equal strengths are taken. The opposite poles of both the magnets are kept at the centre of the magnetic material. Both magnets are stroked, at the same time, from the centre to the opposite ends of the magnetic material being magnetized. This step is repeated many times. Here we can see that end A of the magnetic material becomes the north pole (N) and end B becomes south pole (S). [see page 53, fig: 4.4 double touch method from your book] 3) Electrical method: A long, insulated copper wire is taken. About 300 or more turns of the wire wound around a glass or cardboard tube. The turns of the wire are kept as close together as possible. The ends of the wire are connected to a battery and a switch. A knitting needle is put inside the tube and the current switched on for a short period of time. When the needle is removed from the tube, we will see that the needle behaves like a magnet. [see page 54, fig: 4.5 Electrical method from your book] Demagnetization of a magnet: Demagnetization means loss of magnetic properties of a magnet. Sometimes the magnetism of a bar magnet weakens gradually with time, which is called self demagnetization. There are some ways that can make a magnet lose its magnetic properties. a) dropping a magnet from a far height , b) hitting a magnet with a hammer, c) applying heat to a magnet. Storing magnets: The opposite poles of the two magnets are placed adjacently, and small pieces of soft iron are placed across the ends of the magnets [see book fig: 4.6 storing bar magnets]. These pieces of soft iron are called keepers. Keepers help to retain the magnetism of the bar magnets for a longer time. Uses of magnets: Magnets are used for various purposes and in many devices. 1) Magnets are used in magnetic toys, stickers, doorbells, television sets, audio and video tapes, telephones, generators, loudspeakers, dynamos and computers. 2) Magnets are used in magnetic compasses to help people find directions. 3) Magnets are used in credit cards. 4) Electromagnets are used in cranes to lift heavy loads iron, steel and also used to separate magnetic materials, like iron and steel, from non magnetic materials. 5) Both permanent magnets and electromagnets are used in telephone receivers. Question / Answer (maybe like this): 1. Describe an experiment to show that a freely suspended magnet always aligns itself in a particular direction. Answer: Aim: To show that a freely suspended magnet always aligns itself in a particular direction. Materials required: A wooden stick, a magnet and string. figure: A suspended magnet Procedure: 1) We must tie the magnet with the help of a string to a wooden stick so that it hangs freely. 2) We must note the direction in which the magnet points when it comes to rest. 3) Now we will disturb (rotate) the magnet a little and let it again come to rest and check the direction in which the magnet now comes to rest. Conclusion: We will see that the magnet comes to rest in a particular direction (north -- south). 2. Describe an experiment to find the poles of a magnet. Answer: Aim: To find the poles of a magnet. Materials required: A magnet, a sheet of paper and iron filings. Procedure: 1) We must sprinkle some iron filings on a sheet of paper. 2) We have to roll a bar magnet over the iron filings. 3) We will observe that most of the iron filings get attracted to the two ends of the magnet. Conclusion: Thus, the two poles of a magnet are called the north pole and south pole. 3. Describe an experiment to prove that like poles of a magnet repel each other and unlike poles attract each other. Answer: Aim: to prove that like poles of a magnet repel each other and unlike poles attract each other. Materials required: Two bar magnets and a wooden stand. Procedure: 1) WE have to suspend a bar magnet from a wooden stand and let it come to rest. 2) We have to bring the south pole(S) of another bar magnet close to the north poles(N) of this magnet. 3) Next, we have to bring the north pole(N) of the second magnet close to the north pole(N) of the first magnet. 4) We have to repeat the same thing with the south pole of first magnet and record the observation in the table below.  Conclusion: Poles attract or repel N to N repel S to S repel N to S attract S to N attract The observation shows that like poles of a magnet repel unlike poles attract 4. Describe an experiment to make an electromagnet. Answer: Aim: To make an electromagnet. Materials required: Soft iron bar, a cell/battery, an insulated copper wire, a small safety pin and a switch. Procedure: 1) We have to wrap the copper wire around the soft iron bar. 2) We have to connect the two ends of the copper wire to the terminal of a cell/battery and complete the circuit by closing the switch. 3) We have to bring a safety pin close to the soft iron rod. 4) We will see that the safety pin gets attracted to the soft iron bar and after switch off the safety pin is no longer attracted by the soft iron bar Conclusion: We observed that the soft iron piece behaves like a magnet as long as the current flows in the coiled wire. 5. Describe the method of making a magnet by Single touch method. Answer: Figure: Single touch method (book page—53)  Single touch method: A piece of any magnetic material say AB is taken and placed on a table. A bar magnet is brought close to the magnetic material AB. One end of the bar magnet say north (N) is stroked against the magnetic materials moving from end A to end B. When the bar magnet reaches to end B, it is lifted, and the stroke repeated from end A to end B several times keeping two things in mind: a) the same pole of the bar magnet should be used every time and b) strokes should be in the same direction. By stroking magnetic material with the north pole (N) of the bar magnet, end A becomes the north pole (N) and end B the south pole (S). If we bring the south pole (S) of any bar magnet close to end A, the magnetic material, it will turn into south pole (S) and end B will turn into north pole (N). 6. Describe the method of making a magnet by double touch method. Answer: Figure: double touch method (book page—53) Double touch method: The magnetic material to be magnetized, say AB, is placed on a bench and two bar magnets of equal strengths are taken. The opposite poles of both the magnet are kept at the centre of the magnetic material. Both magnets are stroked, at the same time, from the centre to the opposite ends of the magnetic material being magnetized. This step is repeated many times. Here we can see that end A of the magnetic material becomes the north pole (N) and end B becomes south pole (S). [see fig: 4.4 double touch method from your book]  7. Describe the method of making a magnet by electrical method. Answer: Figure: electrical method (book page—54) Electrical method: A long, insulated copper wire is taken. About 300 or more turns of the wire wound around a glass or cardboard tube. The turns of the wire are kept as close together as possible. The ends of the wire are connected to a battery and a switch. A knitting needle is put inside the tube and the current switched on for a short period of time. When the needle is removed from the tube, we will see that the needle behaves like a magnet. 8. How many types of magnets are based on their shape? Answer: there are several types of magnets based on their shape: a) horseshoe magnet b) ring magnet c) cylinder magnet d) bar magnet. 9. Write the difference between temporary magnet and permanent magnet. Temporary Magnet Permanent magnet 1) Materials that retain their 1) Materials that retain their magnetism only for a short magnetism permanently or period of time are called for long time are called temporary magnets. permanent magnets.  2) Iron and Mumetal are 2) Steel and Alcomax are examples the example of soft of hard magnetic materials used magnetic materials used for making permanent magnet. for making temporary magnet like electromagnet. 10. Write the difference between magnetic materials and non- - magnetic materials. Magnetic materials N0n--magnetic materials 1) Substances that can be 1) Substances that cannot be attracted by magnets attracted by magnets and and which can which themselves cannot be themselves be magnetized are called non- magnetized are called magnetic substances. magnetic substances or ferromagnetic substances. 2) Example of magnetic 2)Example of non—magnetic materials are Iron, materials are Wood, paper, Nickel, Cobalt and their copper, gold. compound. 11. Write all the properties of a magnet. Answer: Properties of a magnet: All magnets have the following properties, a) They attract objects made of iron steel.  b) When a magnet is suspended freely, it comes to rest in the north—south direction. c) The greater part of the magnetism in a magnet is concentrated at the two ends of the magnet which are termed as north pole (N) and south pole (S). d) Like poles of a magnet repel while unlike poles attract. 12. What is an electromagnet? Answer: Electromagnet: A piece of soft magnetic materials like iron bar behaves like a magnet only as long as the wire wound over it carries current. Its magnetism is soon lost when the current in the wire is switched off. A magnet of this type is called an electromagnet. An electromagnet works on the magnetic effect of the current. 13. What is demagnetization? How does a magnet lose its magnetic properties? Answer: De-magnetization of a magnet: Demagnetization means loss of magnetic properties of a magnet. Sometimes the magnetism of a bar magnet weakens gradually with time, which is called self demagnetization. There are some ways that can make a magnet lose its magnetic properties. a) dropping a magnet from a far height , b) hitting a magnet with a hammer, c) applying heat to a magnet. 14. What should we do to prevent self—demagnetization? Answer: book figure page 55: 4.6 storing bar magnets  Storing magnets: The opposite poles of the two magnets are placed adjacently, and small pieces of soft iron are placed across the ends of the magnets. These pieces of soft iron are called keepers. Keepers help to retain the magnetism of the bar magnets for a longer time. 15. Write all the uses of magnet? Answer: Uses of magnets: Magnets are used for various purposes and in many devices. a) Magnets are used in magnetic toys, stickers, doorbells, television sets, audio and video tapes, telephones, generators, loudspeakers, dynamos and computers. b) Magnets are used in magnetic compasses to help people find directions. c) Magnets are used in credit cards. d) Electromagnets are used in cranes to lift heavy loads iron, steel and also used to separate magnetic materials, like iron and steel, from non magnetic materials. Both permanent magnets and electromagnets are used in telephone receivers.  States of matter Definition: 1) Boiling/evaporation: Boiling is when a liquid becomes a vapor by touching a hot surface. 2) Melting: Melting is the change of a solid into a liquid when heat is applied. 3) Freezing: Freezing is a change of state from liquid to solid. 4) Condensation: Condensation is the process by which water vapor in the air is changed into liquid water. 5) Sublimation: The process of changing from a solid to a gas without passing through an intermediate liquid phase. Carbon dioxide, at a pressure of one atmosphere, sublimates. 6) Deposition: Deposition refers to the process in which a gas changes directly to a solid without going through the liquid state. 1) Complete the box with correct changes of state. (For practice) a) b) C)  2 ) Complete the following table comperaing the three states of matter :(For practice) a) Property Liqid Solid Gas a) Volume b) Compressiblility c) Density d) Forces between atoms/molicules e) Movement of atoms /molecules f) Ease to flow g) Expension on heating b) Property Solid Liquid Gas a) Volume b) Compressiblility c) Density d) Forces between atoms/molicules e) Movement of atoms /molecules f) Ease to flow g) Expension on heating c) Property Liqid Gas Solied a) Volume b) Compressiblility c) Density d) Forces between atoms/molicules e) Movement of atoms /molecules f) Ease to flow g) Expension on heating (Read the whole chapter of magnetism and states of matter for F/B, T/F, MCQ, one word answer, definition and short question )