NCERT Solutions Curiosity Chapter 4 –76End-of-chapter exercise — Let us enhance our learning

Book page 74 Updated on2026-09-05

Q1.

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 ______. (iii) The needle of a magnetic compass rests along the ______ direction. (iv) A magnet always has ______ poles.

Answer

Blank	Answer
(i) Unlike poles of two magnets ______ each other, whereas like poles ______ each other.	attract … repel
(ii) The materials that are attracted towards a magnet are called ______.	magnetic materials
(iii) The needle of a magnetic compass rests along the ______ direction.	north-south
(iv) A magnet always has ______ poles.	two

Why each answer is what it is:

(i) The North pole of one magnet and the South pole of another are unlike poles, and they pull together. Two North poles, or two South poles, are like poles and push apart.
(ii) Iron, nickel, cobalt and steel are pulled in; wood, plastic and glass are not, and those are called non-magnetic materials.
(iii) The needle is a small magnet turning freely, and a freely turning magnet always settles along the north-south line because the Earth behaves like a giant magnet.
(iv) Poles occur only in pairs. Break a magnet as many times as you like — every piece still has one North and one South pole.

Q2.

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.

Answer

Statement	T / F	Reason
(i) A magnet can be broken into pieces to obtain a single pole.	False	Every piece, however small, gets a fresh North pole and South pole at the broken face. A single pole cannot exist.
(ii) Similar poles of a magnet repel each other.	True	Like poles (N–N or S–S) always push each other away.
(iii) Iron filings mostly stick in the middle of a bar magnet when it is brought near them.	False	They stick mostly at the two ends — the poles. The middle is almost bare (Activity 4.2, Fig. 4.4).
(iv) A freely suspended bar magnet always aligns with the north-south direction.	True	The Earth itself behaves like a giant magnet and turns the hanging magnet into the north-south line.

Tip: Statement (iii) is the most common trap in tests. Picture Fig. 4.4 — the filings look like two thick beards at the ends, not a belt at the middle.

Q3.

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. Fill in the blanks. Column I: N–N, N–___, S–N, ___–S. Column II: ___, Attraction, ___, Repulsion.

Answer

Use one rule only — like poles repel, unlike poles attract.

Column I	Column II
N – N	Repulsion
N – S	Attraction
S – N	Attraction
S – S	Repulsion

Working, row by row:

Row 1: N and N are like poles → Repulsion
Row 2: the result is Attraction, so the poles must be unlike. With N given, the blank is S
Row 3: S and N are unlike poles → Attraction
Row 4: the result is Repulsion, so the poles must be like. With S given, the blank is S

Tip: Note that N–S and S–N mean the same thing. It does not matter which magnet you name first — only whether the two poles are alike or unlike.

Q4.

Atharv performed an experiment in which he took a bar magnet and rolled it over a heap of steel U-clips (Fig. 4.15). According to you, which of the options given in Table 4.3 is likely to be his observation? (i) A-10, B-2, C-10 (ii) A-10, B-10, C-2 (iii) A-2, B-10, C-10 (iv) A-10, B-10, C-10

Answer

Answer: option (i) — Position A: 10, Position B: 2, Position C: 10.

In Fig. 4.15, A and C are the two ends of the bar magnet (the poles) and B is the middle.

Position A = North pole → attraction is strongest → many clips (10)
Position B = middle → attraction is weakest → very few clips (2)
Position C = South pole → attraction is strongest → many clips (10)

Rolling the magnet over the heap: the two ends pick up many U-clips, the middle picks up hardly any.

Why the other options are wrong: (ii) and (iii) each make one end weak, but both ends of a magnet are equally strong. (iv) makes the middle as strong as the ends, which contradicts what Activity 4.2 showed.

Q5.

Reshma bought three identical metal bars from the market. 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)?

Answer

She should use the test of repulsion — the only sure test of a magnet.

Method. Call the bars 1, 2 and 3. Take them two at a time and bring an end of one near an end of the other, trying both ends each time.

Test bar 1 with bar 2.
Test bar 1 with bar 3.
Test bar 2 with bar 3.

Reading the result.

What she sees for a pair	What it means
The two bars push each other away in some position	Both bars of that pair are magnets
The two bars only attract, whichever way round they are held	One of them is the plain iron bar

Repulsion is seen in exactly one pair → those two bars are the magnets
The bar left out of that pair is the plain iron bar

Why attraction cannot be used: a magnet attracts an iron bar, and a magnet also attracts the unlike pole of another magnet. Attraction therefore proves nothing. But a piece of iron can never repel anything — so repulsion appears only when both objects are magnets.

Another way (also without extra material): touch the end of one bar to the middle of another. If there is a strong pull, the second bar is the iron piece; if the pull is very weak, the second bar is a magnet, because the middle of a magnet is its weakest region.

Q6.

You are given a magnet which does not have the poles marked. How can you find its poles with the help of another magnet which has its poles marked?

Answer

Use the marked magnet's known North pole and watch for repulsion.

Place the unmarked magnet on the table, or on round pencils so that it can move easily.
Bring the North pole of the marked magnet slowly near one end of the unmarked magnet.
If that end is pushed away (repelled), it is the North pole of the unmarked magnet.
If that end is pulled (attracted), it is the South pole.
The other end is then the opposite pole. Mark both ends with a marker pen.

Known N + unknown end → repulsion → that end is N
Known N + unknown end → attraction → that end is S

Why we look for repulsion and not attraction: attraction can also happen if a piece of the magnet is slightly rusty or if some iron is nearby, so it can mislead you. Repulsion happens for one reason only — two like poles. Confirm your result by repeating with the marked magnet's South pole; the answers must be exactly the other way round.

Q7.

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?

Answer

Let the Earth do the job — the Earth is itself a giant magnet, and no second magnet is needed.

Tie a thread to the middle of the bar magnet so that it hangs horizontally and balanced.
Hang it from a stand or a hook in an open place, well away from iron almirahs, grills, mobile phones and steel furniture.
Give it a gentle turn and let it come to rest by itself.
The magnet settles along the north-south line. The end that points towards the north is its North pole; the other end is the South pole. Mark them.

How do you know which side is north? Note where the Sun rose that morning — that is roughly east. Face the rising Sun; north is then on your left hand.

Freely suspended magnet → rests north-south
End pointing north = North (north-seeking) pole
End pointing south = South (south-seeking) pole

Another way: float the magnet on a small piece of thermocol or cork in a bowl of still water. It will slowly turn and settle north-south, just like the compass needle you made in Activity 4.4.

Q8.

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?

Answer

Yes, we can. And the answer is a surprising one.

The reasoning, step by step:

1. The compass needle's North pole points towards the geographic north of the Earth.
2. A pole is pulled only by an unlike pole.
3. So whatever lies near the geographic north must be attracting a North pole.
4. Therefore near the Earth's geographic north there is the South pole of the Earth's magnet.
5. And near the geographic south there is the North pole of the Earth's magnet.

The Earth behaves like a giant bar magnet buried inside it — but turned the other way round, with its magnetic South pole lying near the geographic North.

Why it feels upside down: the names came first and the science later. The end of a magnet was named “North pole” simply because it seeks the north. Once that name was fixed, the rule that unlike poles attract forced the Earth's magnet to have its South pole up near the geographic north.

Q9.

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.

Answer

Magnetise the tip of the screwdriver. Then each steel screw clings to the tip instead of dropping into the machine.

How the mechanic can do it (exactly the method of Activity 4.4):

Lay the screwdriver on a table and take a strong permanent magnet.
Place one pole of the magnet at the handle end of the steel shaft and stroke it along the shaft to the tip, always in the same direction with the same pole.
Lift the magnet away, go back to the starting end and stroke again. Repeat 30 to 40 times.
Test it by touching a steel screw to the tip. If the screw hangs on, the screwdriver is magnetised and ready.

An even quicker fix: stick or tape a small magnet on the shaft near the tip, or use a ready-made magnetic screwdriver.

Why it works: the screwdriver's shaft is made of steel, which contains iron and is therefore a magnetic material. Stroking lines up the tiny magnets inside it, so it becomes a magnet itself and attracts the steel screws.

Tip: A magnetised screwdriver should not be used near a watch, a mobile phone or a compass. And if the tip must be demagnetised later, tapping it hard several times or heating it will do it — which is also why the chapter warns you not to drop, hammer or heat your magnets.

Q10.

Two ring magnets X and Y are arranged as shown in Fig. 4.16. It is observed that the magnet X does not move down further. What could be the possible reason? Suggest a way to bring the magnet X in contact with magnet Y, without pushing either of the magnets.

Answer

The reason: the two facing surfaces of X and Y are like poles (either both North or both South). Like poles repel, so magnet X is pushed upwards. It floats and stops at the height where this upward push exactly balances its own weight, and it cannot come down any further.

Left: like poles face each other, so X hovers above Y. Right: X has been lifted off, turned upside down and slipped back — now unlike poles face and the two magnets come together.

The way to bring them in contact: lift magnet X off the rod, turn it upside down (invert it), and slide it back on. Now an unlike pole of X faces the top pole of Y, so instead of repelling they attract — and X slides down on its own until it rests on Y. No pushing is needed.

Why the ring magnets have their poles on the flat faces: in a ring (or disc) magnet the two poles are the two flat circular surfaces, not the rim. So flipping the ring over swaps which pole faces downward — and that single flip changes repulsion into attraction.

Did you know? A magnet hovering in mid-air on a rod is a classroom-sized Maglev. The same idea of like-pole repulsion lifts a whole train off its track.

Q11.

Three magnets are arranged on a table in the form of the shape shown in Fig. 4.17. What is the polarity, N or S, at the ends 1, 2, 3, 4 and 6 of the magnets? Polarity of one end (5) is given for you.

Answer

Answer: 1 = N, 2 = S, 3 = N, 4 = S, 5 = N (given), 6 = S.

The key idea: the three magnets are lying joined end to end and staying put. Two ends can rest quietly touching each other only if they attract — that is, only if they are unlike poles. If they were like poles they would push apart and the shape would fall open.

End 5 = N (given)
Ends 4 and 5 touch → they must be unlike → end 4 = S
Ends 3 and 4 are the two ends of the same magnet → end 3 = N
Ends 2 and 3 touch → they must be unlike → end 2 = S
Ends 1 and 2 are the two ends of the same magnet → end 1 = N
Ends 5 and 6 are the two ends of the same magnet → end 6 = S

The three bar magnets with all six polarities filled in. Red ends are North poles and blue ends are South poles.

Why you cannot get a different answer: once end 5 is fixed as N, every other end follows with no choice left — each magnet must carry one N and one S, and each joint must be N against S. Starting from the given end and working around the shape is the reliable way to solve any question of this type.

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