Exploring Magnets

The opening story asks how sailors could find direction when stars were hidden. A magnetic compass provides one route. Magnets also hold some pencil-box and purse closures shut and attach some dusters to boards.

Naturally occurring magnets are called lodestones. Artificial magnets are manufactured in shapes such as bars, horseshoes and rings. Shape alone does not tell you how strongly a magnet will act.

In this chapter, magnetic materials are those noticeably attracted by an ordinary magnet: iron, nickel, cobalt and some alloys. Wood, rubber, plastic and glass are examples treated as non-magnetic. Do not assume that every metal, every steel alloy or every shiny object will be attracted.

Separate prediction from observation

For Activity 4.1, record the object, its material, your prediction and the observed result. Bring the same magnet near each object. A pencil or pair of scissors can contain several materials; identify which part responds rather than classifying the whole object by appearance.

In Activity 4.2, iron filings on paper collect much more densely near the ends of a bar magnet than near its middle. The two pole regions are called North and South. This is evidence that the magnetic effect is not equally strong at every position.

Breaking an ordinary magnet does not separate North from South: each smaller magnet has both poles. Treat this as an explanation, not an instruction to break magnets.

Pole locations depend on how a magnet is magnetised. The final textbook page shows bars, discs, cylinders, rings and spheres with different arrangements. Do not infer a ring magnet’s poles from its shape alone. Letters or tested pole markings are more useful than colour, which is only a labelling convention.

Suspend a bar magnet horizontally from its balanced midpoint, turn it gently and let it settle. Repeat and mark its resting direction. Away from other magnets and interfering iron, it tends to return to a north–south alignment. An unmagnetised iron bar does not reliably do this. The north-seeking end is called the North pole.

A compass contains a magnetised needle free to turn on a pivot. Hold the compass level, let the needle settle, then rotate its dial so the marked North agrees with the north-seeking end. Read the other directions from the aligned dial. The red end usually indicates North, but check the instrument’s markings.

Precision note: a compass follows the local horizontal magnetic field, not a line aimed exactly at geographic north. The angle between magnetic north and true north is magnetic declination; it changes with place and time. Nearby magnets and iron can also disturb a reading.

The Earth behaves broadly like a magnet. In the simple bar-magnet analogy, the region near geographic north has south-like magnetic polarity, attracting a compass’s north-seeking pole. Geographic direction names and physical magnetic polarity must not be confused. Magnetism is not the reason objects fall: gravity is a different interaction.

Activity 4.4 turns an iron sewing needle into a simple compass. Work with a teacher or responsible adult: the needle and small pins are sharp. The construction is a demonstration, not a substitute for a navigation instrument.

1. 1

   Stroke in one direction

   Lay the needle on a wooden surface. Move one pole of a permanent magnet from one end to the other, lift it away and return to the starting end. Repeat with the same pole and direction about 30–40 times; do not rub back and forth.

2. 2

   Check that the needle attracts pins

   Bring pins near the needle. Their attraction is evidence that the stroking changed the needle’s behaviour.

3. 3

   Float and compare directions

   Have an adult pass the needle horizontally through cork. Float it in a bowl of water with the needle above the surface. Turn the cork gently, let it settle and repeat. Use an established direction or a trusted compass to identify the north-seeking end; alignment alone does not label the ends.

In Activity 4.5, place one labelled bar magnet on round pencils so that it can move. Bring a second magnet near without touching, then reverse the approaching pole. Unlike poles attract; like poles repel. Compare the facing poles, not the colours at the far ends.

A compass needle is also a magnet. In Activity 4.6, a North pole brought near its north-seeking end makes that end move away; a South pole makes it move towards the approaching magnet. This explains why a nearby magnet can spoil a compass reading.

An unmagnetised iron bar can be attracted by either pole of a magnet. Attraction alone therefore does not prove that an unknown object is already a magnet. Repulsion from a known magnetic pole identifies a like pole of another magnet.

Two magnets and one iron bar

Compare the three bars in pairs, testing both end orientations. The pair that can repel consists of the two magnets; the remaining bar is iron. A single attraction test is insufficient.

Label a known but unmarked magnet

Bring a known North pole near each end. The end that repels it is North; the other end is South. Without another magnet, suspend the unmarked magnet freely and compare its settled direction with an independently established north direction.

Explain separated ring magnets

If an upper ring is supported above another ring on a vertical guide, like facing poles can repel and oppose its weight. Turning one ring over can bring unlike poles together. The rod guides the rings; this example does not show stable, unsupported levitation in every direction.

Activity 4.7 keeps the magnet and compass in the same positions while inserting wood, cardboard, a thin plastic sheet and a thin glass sheet. The textbook reports no appreciable change in deflection for these samples: the magnetic effect can act through them.

Keep the separation and orientation unchanged when comparing barriers. A weaker response after moving the magnet farther away cannot be blamed on the barrier alone. This experiment does not prove that every material or every thickness has no effect.

Follow the action without contact

A magnet beneath cardboard can guide steel balls through a maze. A magnet outside a glass of water can lift a steel paper clip. Like poles on model cars can push them apart. A magnetic garland illustrates attraction between linked objects.

Use further activities to ask better questions

The textbook proposes a hopping-frog model using successive ring magnets and comparing how many pins different magnets lift. Keep pin type, contact and test conditions comparable before judging strength. Maglev and medical uses are further research prompts; this elementary experiment alone does not explain those technologies.

A historical navigation example

NCERT describes matsya-yantra: magnetised fish-shaped iron floating in oil and used for sea navigation in India. The chapter does not establish an exact invention date or priority claim.

Avoid heating, dropping or hammering magnets, which can weaken them. Follow the textbook’s advice to keep them away from mobile phones and remote controls; do not use sensitive devices as experimental objects.

Store two bar magnets side by side with unlike poles at the same end, a wooden spacer between their long sides and soft-iron pieces across the two ends. Each iron keeper bridges a North pole and a South pole. The diagram shows the arrangement from above.

Use these prompts to retrieve the ideas rather than rereading a second summary. Explain the observation or test that supports each answer.

1. Properties and comparisons · questions 1–4

   Can you complete all four facing-pole combinations? Explain why breaking a magnet leaves two poles, why filings concentrate near a bar’s ends, and why a freely suspended magnet settles repeatedly. For the pin-count table, compare ends with middle; the lesson does not predict a universal exact pin count.

2. Identification and direction · questions 5–8

   Plan the three-bar repulsion test, label an unmarked magnet with and without a known magnet, and explain Earth’s south-like polarity near geographic north. Separate what is observed from what is inferred.

3. Applications · questions 9–11

   Explain how stroking a suitable screwdriver can help it hold steel screws, and how reversing one ring changes the floating-ring setup. In the textbook’s three-magnet arrangement, start from the given N pole at end 5: end 6 is S; touching unlike ends make 4 S, 3 N and 2 S, leaving end 1 N. Each whole bar still has one N and one S.

4. A fair comparison · further learning

   Choose a magnet application and identify the responding material, pole orientation and distance. If comparing magnets, change only what you intend to test. Explain why a changed shape does not remove the need to identify both poles.

Choose an answer and check the reasoning. These original questions test the chapter’s concepts; they are not presented as UPSC previous-year questions.