Textbook-based subjective questions

Reshma lives in a coastal town of Kerala and is very fond of writing short stories.

The story was based on a ship carrying spices from Kerala for trade in the olden days.

Reshma was aware that in those days, the sailors used stars to find directions at night. But in her story, a situation arose wherein the sailors got caught in a storm with an overcast sky and stars were not visible.

Reshma could not take her story forward as she could not think of a way for sailors to find directions. She searched for information on the internet and her school library.

She learnt that the travellers used a device, known as a magnetic compass, for finding directions. Reshma had seen pencil boxes and purses which had magnets to keep them closed. A writing board in her school also had a duster with a magnet.

Reshma had seen pencil boxes and purses which had magnets to keep them closed. A writing board in her school also had a duster with a magnet. But she had never looked at those carefully.

But she had never looked at those carefully.

The magnets used by sailors in the olden days were based on naturally occurring magnets, known as lodestones which were discovered in ancient times.

Later on, people found out that magnets could also be made from pieces of iron. Nowadays, we have magnets made of different materials.

The magnets that you find in your school laboratory and those used in pencil boxes, stickers, toys are all artificial magnets (Fig. The magnets can be of various shapes, some of which are shown in Fig.

Activity 4.1: Let us explore Collect a few objects made of different materials and also a magnet. Predict which of the objects will stick to the magnet. Write your prediction in Table 4.1. Now hold a magnet in your hand and bring it near the objects one by one (Fig. Observe which of the objects stick to the magnet.

Observe which of the objects stick to the magnet. Material which the Attracted by the Name of the object is made of magnet (Yes/No) object (plastic/wood/glass/ iron/any other) Prediction Observation Was your prediction correct for all objects?

Material which the Attracted by the Name of the object is made of magnet (Yes/No) object (plastic/wood/glass/ iron/any other) Prediction Observation

Through this activity, we found out that some of the objects were attracted to the magnet and stuck to it, while others were not.

The metal iron is a magnetic material. Do all parts of a Nickel and cobalt are other metals that are magnet attract also magnetic.

Do all parts of a Nickel and cobalt are other metals that are magnet attract also magnetic. magnetic with other metals are also attracted materials towards magnets.

The materials which are equally? not attracted towards a magnet are called non-magnetic materials. Which materials listed in Table 4.1 were found to be non-magnetic? 4.2 Poles of Magnet Activity 4.2: Let us investigate Spread some iron filings (very small pieces of iron) on a sheet of paper. Place a bar magnet over them.

4.2 Poles of Magnet Activity 4.2: Let us investigate Spread some iron filings (very small pieces of iron) on a sheet of paper. Place a bar magnet over them. Tap the paper and observe carefully what happens to the iron filings. Do you observe anything special about the way they stick to the magnet?

Tap the paper and observe carefully what happens to the iron filings.

Do the iron filings stick all over the magnet uniformly?

We find that maximum iron filings stick near the ends of the bar magnet, as shown in Fig. If we repeat this activity with magnets of other shapes, do we get the same result?

If we repeat this activity with magnets of other shapes, do we get the same result? 4.4: Iron filings sticking to a bar magnet

two poles of the magnet—the North pole and a magnet the South pole. Most of the iron filings stick with a to the poles of a magnet of any shape. single pole? It is not possible to obtain a magnet with a single pole.

It is not possible to obtain a magnet with a single pole. If a magnet is broken into smaller pieces, North and South poles always exist in pairs even in the smallest piece of the magnet. A single North pole or a South pole cannot exist.

If a magnet is broken into smaller pieces, North and South poles always exist in pairs even in the smallest piece of the magnet.

4.3 Finding Directions Activity 4.3: Let us experiment Suspend a bar magnet with a thread tied to the middle of the magnet as shown in Fig.

Join these two points on the ground with a line. This line indicates the direction along which the magnet comes to rest. Now again rotate the magnet by giving a gentle push at its one end and wait till it Fig.

4.5: A freely suspended bar magnet comes to rest. Does the magnet rest along the same line?

Does the magnet rest along the same line? Wha td this irection If we have noticed the direction lin d alon e indic oes where the Sun rises or sets, we g a te Exploring Magnets mag wh net r ich the have an approximate idea of can e we fi sts?

mag wh net r ich the have an approximate idea of can e we fi sts? Hence, we nd i t ou can locate the direction along t? which the magnet rests. A freely suspended magnet comes to rest along the north-south direction.

A freely suspended magnet comes to rest along the north-south direction.

The end of the magnet that points towards north direction is called the North-seeking pole or the North pole of the magnet.

A freely suspended magnet rests along the north-south direction because our Earth itself behaves like a giant magnet. Repeat this activity with a small iron bar in place of the bar magnet.

Does it always rest along north-south direction? This implies that only magnets rest along north-south direction.

This implies that only magnets rest along north-south direction. This activity provides us with a way to test whether a piece of metal is a magnet or not. The property of a freely suspended magnet to always rest along the north-south direction is used to find directions.

The property of a freely suspended magnet to always rest along the north-south direction is used to find directions. Based on this, a small device called a magnetic compass was developed in olden days for finding directions. It has a magnet in the shape of a needle which can rotate freely (Fig.

It has a magnet in the shape of a needle which can rotate freely (Fig.

The needle of a magnetic compass indicates the north-south direction.

After some time, the needle comes to rest in the north-south direction. The compass box is then gently rotated until the north and south marked on the dial are aligned with the needle.

4.6: A magnetic are as indicated on the dial. compass How can we A magnetic compass is usually a small circular box make our with a transparent cover on it, as shown in Fig.

How can we A magnetic compass is usually a small circular box make our with a transparent cover on it, as shown in Fig. 4.6. own magnetic The magnet, in the shape of a needle, is mounted compass? on a pin standing on the bottom of the box. This needle is balanced on the pin in such a manner that it can move around this point easily, that is, it can rotate freely.

This needle is balanced on the pin in such a manner that it can move around this point easily, that is, it can rotate freely. The end of the needle which rests in the North direction More to is usually painted red. Below the needle, know! there is a dial with directions marked on it.

Below the needle, know! there is a dial with directions marked on it.

Then keep any one pole of the magnet at one end of the needle.

Move the magnet over the needle along its length as shown in Fig. When it reaches the other end of the needle, lift it up. Bring the same pole of the magnet you started Fig.

4.7(a): Making an iron with to the same end of the sewing needle from needle a magnet which you began, and repeat the previous step. Repeat this process at least 30 to 40 times. Bring some iron filings or steel pins near the needle.

If the pins or iron filings get attracted to the needle, then that means that the needle has become a magnet. Pass this needle through the cork horizontally. Float the cork in a glass bowl filled with water, such that the needle always remains above the level of water as shown in Fig. 4.7b. When the needle comes to rest, your magnetic Fig.

Float the cork in a glass bowl filled with water, such that the needle always remains above the level of water as shown in Fig. 4.7b. When the needle comes to rest, your magnetic Fig. 4.7(b): A compass needle compass is ready for use.

4.7(b): A compass needle compass is ready for use.

Do the ends of the needle always point in the same direction?

What happens when we bring Much before the widespread use of the modern two magnets magnetic compass (Fig. 4.6), a device similar to closer to each the compass needle made by you (Fig.

4.7b) was other? used by Indians for navigation at Exploring Magnets It consisted of a magnetised fish-shaped iron piece, kept in a vessel of oil.

It was called Do you matsya-yantra (or machchh- know? yantra). 4.4 Attraction and Repulsion between Magnets Activity 4.5: Let us experiment Take a pair of bar magnets on which North and South poles have been marked. Mark the two bar magnets as A and B. Place the longer side of magnet A over 5–6 round shaped pencils as shown in Fig.

4.4 Attraction and Repulsion between Magnets Activity 4.5: Let us experiment Take a pair of bar magnets on which North and South poles have been marked. Mark the two bar magnets as A and B. Place the longer side of magnet A over 5–6 round shaped pencils as shown in Fig. 4.8a. Now bring one end of magnet B near the end of magnet A placed on the pencils.

4.8a. Now bring one end of magnet B near the end of magnet A placed on the pencils.

Observe what happens. Next, bring the other end of magnet B near the same end of magnet A (Fig.

Does the magnet A on the pencils begin to move? Does it always move in the direction of the approaching magnet?

You will see that unlike poles of two magnets, that is, the North pole of one magnet and the South pole of another magnet, attract each other. The like poles, that is, either the North poles or the South poles of both magnets, repel each other.

Repeat the activity by using an iron bar in place of one of the magnets. You will find that both the ends of the iron bar will be attracted by both the North and South poles of the magnet. From this activity, we find that a magnet can be identified by its property of repulsion.

From this activity, we find that a magnet can be identified by its property of repulsion. Activity 4.6: Let us experiment Take a magnetic compass and a bar magnet. The compass needle Place the magnetic compass over is also a magnet.

Activity 4.6: Let us experiment Take a magnetic compass and a bar magnet.

Will a horizontal surface and wait it show the same for its needle to come to rest. behaviour if a magnet is brought closer to it? Now slowly bring North pole of the bar magnet close to the North pole of the compass needle as shown in Fig.

Do you observe any difference this time? When the North pole of a magnet is brought closer to the North pole of the compass needle, it moves away as shown in Fig.

When the North pole of a magnet is brought closer to the North pole of the compass needle, it moves away as shown in Fig. When the South pole of the magnet is brought closer to the North pole of the compass needle, it moves closer (Fig.

Suppose we place a piece of wood between the compass needle and the magnet. Will this affect the deflection of the compass needle? Repeat the first or second part of Wood Activity 4.6. Without disturbing the bar magnet and magnetic compass, place a piece of wood between them, perpendicular to the table as

Repeat the first or second part of Wood Activity 4.6. Without disturbing the bar magnet and magnetic compass, place a piece of wood between them, perpendicular to the table as Observe the with a piece of wood in between compass needle carefully. Is there any effect on the deflection of compass needle due to the piece of wood? Record your observation in Table 4.2. Repeat the process by replacing the piece of wood with a cardboard sheet, thin plastic sheet, and a thin glass sheet.

Observe the with a piece of wood in between compass needle carefully. Is there any effect on the deflection of compass needle due to the piece of wood?

You would observe that there is no appreciable change in the deflection of the needle when a sheet of any of the above material is placed between the magnet and the compass needle.

4.5 Fun with Magnets After learning about magnets, Reshma was excited and decided to set up some fun activities using magnets at her school fair. You may try making these yourself and may also think of some more fun ideas.

You may try making these yourself and may also think of some more fun ideas. Magnets can move some objects without touching them!

Can we take the steel balls out of the maze by moving a magnet below the cardboard tray? 4.12) Can we pick out a steel paper clip fallen in water using a magnet, without getting our fingers or the magnet wet? Will the two cars speed towards each other or run away from each other when brought closer?

Will the two cars speed towards each other or run away from each other when brought closer? 4.14: Two matchbox-magnet cars with like poles of the magnets facing each other In some magnets, the North and South poles are marked as N and S.

4.14: Two matchbox-magnet cars with like poles of the magnets facing each other

In some other magnets, the North pole is indicated by a white dot.

Magnet says, N S Iron “Store me properly. Keep piece S N me in pairs with unlike poles on the same side.

Wooden piece Keep a piece of wood in between. Place two pieces of soft iron across the ends.” Caution “Do not heat me or drop me Have fun, More to or hammer me. but treat know!

Place two pieces of soft iron across the ends.” Caution “Do not heat me or drop me Have fun, More to or hammer me. but treat know! Do not keep me near mobile magnets phones or remote controls.” with care. Summary A magnet has two poles—the North pole and the South pole. The poles of a magnet always exist in pairs.

Summary A magnet has two poles—the North pole and the South pole. The poles of a magnet always exist in pairs. A single North pole or a single South pole cannot exist. Magnetic materials are the materials that are attracted towards a magnet. Non-magnetic materials are the materials that are not attracted towards a magnet. A freely suspended magnet rests along the north-south direction. The needle of a magnetic compass indicates the north-south direction. When two magnets are brought close to each other, like poles (North-North, South-South) repel each other while unlike poles (North-South) attract each other. Fill in the blanks (i) Unlike poles of two magnets each other, whereas like poles each other.

Fill in the blanks (i) Unlike poles of two magnets each other, whereas like poles each other.

(ii) The materials that are attracted towards a magnet are called .

State whether the following statements are True (T) or False (F). (i) A magnet can be broken into pieces to obtain a single pole. [ ] (ii) Similar poles of a magnet repel each other. [ ] (iii) Iron filings mostly stick in the middle of a bar magnet when it is brought near them. [ ] (iv) A freely suspended bar magnet always aligns with the north-south direction. [ ]

Column I shows different positions in which one pole of a magnet is placed near that of the other. Column II indicates the resulting interaction between them for different situations.

Column II indicates the resulting interaction between them for different situations. Atharv performed an experiment in which he took a bar magnet and rolled it over a heap of steel U-clips (Fig. A B C According to you, which of the Fig.

A B C According to you, which of the Fig. 4.15: Bar magnet and heap options given in Table 4.3 is likely of steel U-clips to be his observation? Out of these bars, two were magnets and one was just a piece of iron.

Out of these bars, two were magnets and one was just a piece of iron.

How will she identify which two amongst the three could be magnets (without using any other material)?

How can you find its poles with the help of another magnet which has its poles marked? A bar magnet has no markings to indicate its poles.

How would you find out near which end its North pole is located without using another magnet? If the earth is itself a magnet, can you guess the poles of earth’s magnet by looking at the direction of the magnetic compass?

If the earth is itself a magnet, can you guess the poles of earth’s magnet by looking at the direction of the magnetic compass? While a mechanic was repairing a gadget using a screw driver, the steel screws kept falling down. Suggest a way to solve the problem of the mechanic on the basis of what you have learnt in this chapter.

Suggest a way to solve the problem of the mechanic on the basis of what you have learnt in this chapter. Two ring magnets X and Y are arranged as shown in Fig. It is observed that the magnet X does not move down further.

It is observed that the magnet X does not move down further.

4.16: Two ring magnets contact with magnet Y, without pushing either of the magnets.

Three magnets are arranged on a table in the form of the shape 3 shown in Fig. What is the 1 polarity, N or S, at the ends 1, 2, 3, 4 and 6 of the magnets?

Polarity 6 of one end (5) is given for you. Using 3–4 different magnets, try to lift steel pins or U-clips and check which magnet picks up the largest number of pins.

Discuss with your friends why different magnets might have picked up different numbers of pins. Make a toy ‘Hopping Frog’ as a combined class activity with the help of your teacher. For constructing the toy, fix ring magnets in an alternate North-South fashion along the Paint a frog on paper, cut along the outline and glue a ring magnet at its base.

For constructing the toy, fix ring magnets in an alternate North-South fashion along the Paint a frog on paper, cut along the outline and glue a ring magnet at its base. Take a transparent, flexible plastic strip (Fig.

Take a transparent, flexible plastic strip (Fig.

When you slide the plastic strip (with frog) over the scale (Fig.

4.18b), you can observe the frog hopping. Find out about the Maglev Train and try to make its model. Try to find out why there is a need to make magnets of different shapes. Magnet says “Humans have made me in to o re different shapes and sizes as per their M ow! kn requirements.

Magnet says “Humans have made me in to o re different shapes and sizes as per their M ow! kn requirements. However, my poles always occur in pairs, no matter my shape”.