Chapter 13: Fun with Magnets

    I. Multiple Choice Questions (MCQs).
    Q.1. Maglev train has no
    a) engine
    b) wheel
    c) driver
    d) none of these

    Answer: b) wheel

    Q.2. A black coloured rock was discovered, which could attract small pieces of iron, it was called
    a) magnetite
    b) magnet
    c) magnesia
    d) none of these
    Answer: a) magnetite
    Q.3. Magnetite is an ore of an iron called
    a) ferric oxide
    b) magnetic oxide
    c) metallic oxide
    d) none of these
    Answer: (a) ferric oxide
    Q.4. The lodestone or leading stone is called
    a) artificial magnet
    b) magnetite
    c) natural magnet
    d) both (b) and (c)
    Answer: (c) natural magnet
    5. The two ends of a bar magnet are called
    a) outer ends
    b) inner ends
    c) poles
    d) none of these
    Answer: (c) poles
    II. Fill in the blanks by selecting appropriate words from the given list :
    List : Electromagnet, pairs, magnet, strongest, pivoted
    Q.1. We can separate magnetic particles with the help of a _______________.
    Q.2. Magnetic force is the _______________ at two ends of a bar magnet.
    Q.3. Magnetic poles always exist in _______________.
    Q.4. A compass consists of a magnetised needle _______________ at a point.
    Q.5. _______________ is a special magnet where magnetism is produced by flow of electric current.

    Answer: 1- magnet,
    2- strongest,
    3- pairs,
    4- pivoted
    5- Electromagnet

    III. Match the items of Column A with those of Column B.

    Answer: 1-c, 2-d, 3-b, 4-e, 5-a

    IV. Write ‘T’ for the true and ‘F’ for the false statements.
    Q.1. A magnet is a material that attracts certain substances, such as iron, called magnetic substance.
    Q.2. Earth itself is a huge magnet having its magnetic north and south poles.
    Q.3. Whether the magnets attract or repel themselves, depends upon their strengths.
    Q.4. Attraction is the surest test of magnetism.
    Q.5. Magnets tend to become weaker after some time if their poles are left free. Ans: 1-T, 2-T, 3-F, 4-F, 5-T

    V. Very Short Answer Questions.
    Q.1. Write two household devices in which magnet is used.

    Answer: door bells and televisions
    Q.2. Where was magnet discovered?
    Answer: Magnet was discovered thousands of years ago at Magnesia in Asia Minor.

    Q.3. What was the name given for magnetite by the Chinese?
    Answer: Lodestone

    Q.4. Write three magnetic substances.
    Answer: Iron, cobalt and nickel

    Q.5. Write three non-magnetic substances.
    Answer: Aluminium, copper and brass

    VI. Short Answer Questions.

    Q.1. How was magnet discovered?

    Answer: Magnet was discovered thousands of years ago at Magnesia in Asia Minor. A black coloured rock was discovered, which could attract small pieces of iron. It was called Magnetite.

    Q.2. Write the kinds of artificial magnet and use of one of them also.

    Answer: Artificial magnet can be temporary or permanent depending on the method used. Magnet used in separating magnetic materials from non-magnetic materials.

    Q.3. What do you mean by magnetic and non-magnetic substances?

    Answer: A magnet has an interesting property that it attracts certain substances towards itself. However, some substances do not get attracted towards magnet. The substances attracted by a magnet, are called magnetic substances. For examples: iron, cobalt, nickel, etc. The substances not attracted by magnet are called non-magnetic substances. For examples:
    aluminium, copper, brass, plastic, etc.

    Q.4. Describe with an experiment that how you can separate magnetic substances from sand or soil obtained from different places.
    Answer: To separate magnetic substances from sand or soil obtained from different places we need sample of soil or sand from different places, paper and magnet.

    Lorem ipsum dolor sit amet, consectetur adipiscing elit. Ut elit tellus, luctus nec ullamcorper mattis, pulvinar dapibus leo.Procedure : Spread one of the sample on paper. Take magnet and rub it in the sample. Pull out the magnet. Magnetic substances (i.e., iron filings) present in the sample stick to the magnet. Now, remove it from magnet on the other paper. Repeat this activity till the no substance sticking to the magnet. Similarly, repeat same activity for all the samples. In this way you can separate magnetic substances from sand or soil obtained from different places.

    Q.5. What do you mean by poles of a magnet? Describe with an experiment that how you can find the poles of a magnet.

    Answer: A magnet has two poles. The two ends of a bar magnet are called poles. At these two points, the magnetic forces are strongest.

    To find the poles of a magnet you need iron nails, sheet of paper and bar magnet.
    Procedure : Place a sheet of paper on the table or on the floor. Spread some iron nails on the sheet of paper. Roll a bar magnet on this sheet of paper and lift it up. What do you find? You find that the iron nails are sticked more near the region close to two ends of a bar magnet. Conclusion : From this activity you can concluded that magnetic force is the strongest at two ends of a bar magnet and hence, called its poles.

    Q.6. Discuss how magnetic poles always exist in pairs with suitable examples.

    Answer: Two poles of any magnet cannot exist independently. They remain in pairs. If a bar magnet is broken into two pieces, each piece behaves as a whole magnet. It means, new pole (opposite in nature) has been produced the moment when it is cut into two pieces. If again, these two pieces are further divided into two pieces each, you will see that again each piece behaves as a whole magnet. From this, we can conclude that magnetic poles always exist in pairs.

    VII. Long Answer Questions.
    Q.1. What do you mean by directional property of a magnet? How can you prove that a freely suspended magnet always points in the geographic north-south direction? Answer: Magnets were known to people from ancient times. In ancient times, the primary use of a magnet was in finding directions. Ancient people knew that if a magnet is freely suspended, it always comes to rest in a particular direction, i.e., north-south direction. This property is used to find directions anywhere on the earth. This is known as directional property of a magnet.

    To prove that a freely suspended magnet always points in North-South direction you need a bar magnet, unspin thread, magnetic needle, sheet of paper, and wooden stand.

    Procedure : Take a bar magnet with marking N for north pole and S for south pole. Tie it from thread at the middle. Now suspend it from a wooden stand. Ensure that the magnet can move freely. Leave the magnet undisturbed for some time and see in which direction it comes to rest. In the meantime mark the directions north and south on the paper with the help of needle. When magnet comes to rest mark its directions. Compare this with the direction you have marked on the paper. Now, give a gentle twist to magnet in any direction and let it come to rest. You will observe that the magnet comes to rest in north-south direction. The end of the magnet that points to the north is called the North pole. The end of the magnet that points to the south is called the South pole.

    Q.2. How can you make a magnet? Describe with an experiment that how you can observe the action between two like poles and unlike poles. Explain briefly with diagrams.
    Answer: There are several methods of making magnets such as
    • Single touch method,
    • Double touch method, and
    • With the help of an electric current

    Here we will will learn about single touch method. In this method we take a magnetic substance (which could be magnetised) say iron bar. Now take a bar magnet and put one of its poles (say N) near one edge of substance and move it along the length of substance till you reach the other end. Then left the bar magnet and bring it down once again over the first end and repeat the above procedure about 40-50 times. Test whether the substance has become a magnet. Also, test the polarity at the ends. You will find that first end of substance has becomes North Pole and other has becomes South Pole.

    Q.3. Write the processes of demagnetisation briefly. How can you store magnets so that they cannot lose their magnetism?

    Answer: A magnet can be demagnetised by the following processes:
    (a) By hammering the magnet.
    (b) Heating the magnet above a certain temperature.
    (c) Dropping a magnet from a certain height.
    Magnets tend to become weaker after some time if their poles are left free. This is called self demagnetisation. So, it has to be stored in a special way. Thus, bar magnets are kept in pairs with their unlike poles on the same side. The pairs of bar magnets are separated by a piece of wood while strips of irons are placed across both ends. These strips of soft iron used to store magnets safely are called magnetic keepers. Magnets must be kept away from mobiles, cassettes, television, CDs and computer as they are weakened by the magnets.

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