Chapter: 07. Magnetism
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The two ends of a magnet are called The magnetic force is maximum at a. both the poles of a magnet. The imaginary line joining the two poles of a magnet is called Which of the following poles attract each other? Which of the following is the surest test of magnetism? Frame a question on the properties of magnets and discuss the answer in the class. Question: How does a magnet’s directive property assist in finding geographical directions, and what makes it reliably point north-south? Answer: The directive property of a magnet means that when freely suspended, it always aligns itself in the geographic north-south direction. This happens because the Earth itself acts as a giant magnet, with its magnetic south pole located near the geographic north pole and its magnetic north pole near the geographic south pole. The north pole of the suspended magnet is attracted to the Earth’s magnetic south pole, thus pointing geographically north, and similarly for the south pole. REASON CORNER
Why is a compass needle kept in a glass casing? A compass needle is kept in a glass casing to protect it from external disturbances such as air currents (wind), dust, and physical damage, ensuring that it can swing freely and accurately without obstruction to indicate the Earth’s magnetic north-south direction. You are given two rods. Out of these, one is an iron rod and the other one is a magnet. How will you identify these rods? To identify the rods, bring one end of an unknown rod (let’s call it Rod A) near the middle of the other unknown rod (Rod B). If Rod A is attracted to the middle of Rod B, then Rod A is an iron rod and Rod B is the magnet (because the magnetic force is weakest or non-existent at the center of a magnet). Alternatively, and more conclusively, bring both ends of Rod A, one by one, near one pole (e.g., the North pole) of Rod B. If one end of Rod A is attracted and the other end is repelled by the North pole of Rod B, then both Rod A and Rod B are magnets. If both ends of Rod A are attracted to the North pole of Rod B, then Rod A is an iron rod, and Rod B is the magnet. Repulsion is the surest test of magnetism. MY QUESTION TIME
a. Magnetisation
* Question: Describe two distinct methods, other than using electric current, by which a non-magnetic steel rod can be permanently transformed into a magnet.
* Answer: Two methods to permanently magnetize a steel rod are the single touch method and the double touch method. In the single touch method, a single bar magnet is rubbed along the length of the steel rod repeatedly in one direction, lifting the magnet after each stroke and returning it to the starting point without touching the rod. In the double touch method, two bar magnets with opposite poles are placed at the center of the steel rod and simultaneously rubbed outwards towards the ends, then lifted and brought back to the center, repeating this process multiple times.
b. Types of Magnets
* Question: Explain the fundamental differences between a permanent magnet and a temporary magnet, considering their material composition and the stability of their magnetic properties.
* Answer: A permanent magnet is typically made of steel and retains its magnetic properties for a long time, having fixed north and south poles and a constant strength. In contrast, a temporary magnet is usually made of soft iron, retains its magnetic properties only temporarily or while under the influence of an external magnetic field/current, and its pole positions and strength can vary.
EUAGDAGDOG
A. Choose the correct option.
Which of the following is not a magnetic material? Which of the following statements is false? c. The two poles of a magnet can be separated. A magnet does not lose its property if it is Which of the following was the first magnet discovered? The imaginary line joining the two poles of a magnet is called Four ring magnets P, Q, R and S are placed as shown in the figure. Which magnet should be flipped so that all magnets are attracted to each other? (Cannot be answered without the accompanying image) The specific magnet to be flipped depends on its current orientation relative to the others in the provided diagram. To achieve attraction between all magnets, their poles must alternate (e.g., North-South, South-North, North-South, etc.) in sequence. The magnet that is disrupting this alternating pattern would be the one to flip. B. Fill in the blanks.
The region around the magnet where its magnetic influence can be felt is called the magnetic field of a magnet. Magnets are used in dynamos of bicycles and automobiles. Magnetite is an ore of iron. Magnetic lines of force never intersect each other since they repel each other. While storing the magnets, a piece of wood should be kept between them. C. Write true (T) or false (F) against the following statements.
A temporary magnet has fixed north and south poles. Force of attraction is strongest at the centre of the magnet. The direction of magnetic lines of force is always from the north pole to the south pole externally. The strength of an electromagnet decreases with increase in the number of turns of the coil. A magnet always aligns itself in the north-south direction when suspended freely. D. Match the following:
two ends of a magnet - b. poles wood and glass - c. non-magnetic closed continuous curves - d. magnetic lines of force magnets made from soft iron - a. temporary magnets E. Short answer type questions.
What is a magnet? Give four examples each of magnetic and non-magnetic materials. A magnet is any substance that has the property of attracting iron and other materials such as steel, cobalt, and nickel. Four examples of magnetic materials: iron, steel, cobalt, nickel. Four examples of non-magnetic materials: paper, wood, glass, plastic. State the directive property of a magnet. The directive property of a magnet states that when suspended freely, a magnet always aligns itself in the geographic north-south direction. Define electromagnet. How can it be made a permanent magnet? An electromagnet consists of a soft-iron core that becomes magnetized when an electric current is passed through a coil of wire wound around it. An electromagnet can be made a permanent magnet by using a steel piece as the core instead of a soft iron piece, as steel has better retentivity of magnetism. Write two uses of a magnet. Magnets are used in making a magnetic compass for finding directions. Magnets are used in refrigerator doors to create a tight seal. Write two differences between a permanent magnet and a temporary magnet. Permanent magnets have magnetic properties that are permanent, while temporary magnets have magnetic properties that are temporary. Permanent magnets are usually made of steel, whereas temporary magnets are usually made of a soft iron piece. What is magnetic induction? What type of magnets can be made by this method—temporary or permanent? Magnetic induction is the phenomenon by which an ordinary piece of iron acquires magnetic properties temporarily due to the presence of another magnet near it. Only temporary magnets can be made by this method. F. Long answer type questions.
1. Explain how you will test the attractive property of a magnet.
* To test the attractive property of a magnet, you would gather various small objects, including known magnetic substances (e.g., iron nails, steel paper clips, nickel coins) and non-magnetic substances (e.g., a piece of paper, a wooden stick, a glass marble). Bring the magnet close to each object one by one. You will observe that the magnet will pull or attract the magnetic substances towards itself, making them stick to the magnet, while it will have no noticeable effect on the non-magnetic substances. This demonstrates the magnet’s attractive property.
2. Differentiate between single touch method and double touch method of magnetisation.
* Single Touch Method: In this method, a single bar magnet is used to magnetize a magnetic material (like a steel rod). The magnet is rubbed along the length of the material repeatedly, always moving in one direction from one end to the other, lifting the magnet after each stroke and returning it to the starting point without touching the material. This method is simpler but generally produces a magnet of moderate strength.
* Double Touch Method: This method uses two bar magnets of equal strength. Their opposite poles are placed at the center of the magnetic material (e.g., a steel rod) and then simultaneously rubbed outwards towards the ends. After reaching the ends, the magnets are lifted and brought back to the center (without touching the material on the return path). This process is repeated many times and generally produces a stronger magnet than the single touch method.
3. Explain how magnets can be stored.
* Magnets should be stored properly to prevent them from losing their magnetic properties (demagnetisation). This is typically done using magnetic keepers, which are pieces of soft iron. For bar magnets, they should be stored in pairs with their opposite poles placed side by side. A piece of non-magnetic material, such as wood, should be placed between them to keep them separated. Additionally, two soft iron keepers should be placed across the poles at each end of the paired magnets, creating a closed magnetic circuit that helps preserve their strength. For horseshoe or U-shaped magnets, only one soft iron keeper is required, placed across their poles.
4. Write five ways to demagnetise a magnet.
* Five ways to demagnetise a magnet are:
1. Heating: Heating the magnet to a very high temperature (above its Curie temperature).
2. Dropping: Repeatedly dropping the magnet from a significant height.
3. Hammering: Repeatedly hammering or striking the magnet.
4. Contact with Like Poles: Repeatedly bringing the magnet into contact with the like poles of other strong magnets.
5. Electric Current: Passing a strong alternating electric current through the magnet.
6. Self-Demagnetisation: Leaving the poles of the magnets bare and unprotected for a long time.
Higher Order Thinking Skills (HOTS)
Sohan has a bar magnet and three rods labelled A, B and C, and each end of the rod labelled X and Y. He brought the two poles of the bar magnet near each end X and Y of the rods. He recorded the results as follows:
Fill in the blanks with a magnet / non-magnetic material / magnetic material.
a. Rod A: magnet (Repulsion is the surest test of magnetism, confirming Rod A is a magnet.)
b. Rod B: magnetic material (Since both ends were attracted to one pole of the bar magnet, it indicates it’s a material that can be attracted by a magnet but is not itself a magnet.)
c. Rod C: non-magnetic material (No effect from the magnet means it is not attracted at all.) Which of the following arrangements best illustrates how iron filings kept near two magnets will arrange themselves? (Both a and b are valid and commonly used illustrations.) a. This arrangement best illustrates the magnetic field pattern when two magnets are attracting each other (unlike poles facing). Iron filings would form lines connecting the North pole of one magnet to the South pole of the other. b. This arrangement best illustrates the magnetic field pattern when two magnets are repelling each other (like poles facing). Iron filings would show lines diverging and pushing away from the space between the like poles. Both are classic demonstrations of magnetic field lines around two magnets. The “best” choice depends on the specific concept the question intends to emphasize. Virtual Tour
Which type of magnet was used to magnetise the iron needle in the video? A permanent magnet (such as a bar magnet) was used to magnetise the iron needle in the video. What precaution was taken while placing the cork in which the magnetised needle was inserted in the water tub? The precaution taken was to place the cork with the magnetised needle very gently and centrally in the water tub. This ensures that the cork floats freely without touching the sides or bottom of the tub, allowing the magnetised needle to rotate unobstructed and align accurately with the Earth’s magnetic field. 
Answers to textbook exercises
