Chapter 4 Important Questions: Exploring Magnets

✔ Correct Answer: (c) Iron

Iron is a magnetic material because it is attracted towards a magnet. Wood, glass, and plastic are non-magnetic materials and are not attracted by a magnet.

✔ Correct Answer: (b) At the ends (poles) of the magnet

The poles of a magnet are the regions where the magnetic force is strongest. Iron filings cluster maximally at the North and South poles and very few stick to the middle portion.

✔ Correct Answer: (b) North–South direction

A freely suspended magnet aligns itself along the North–South direction because the Earth itself behaves like a giant magnet, attracting the poles of the suspended magnet.

✔ Correct Answer: (b) They repel each other

$\text{Like poles} \Rightarrow \textbf{Repulsion}$

Like poles (N–N or S–S) of two magnets always repel each other, while unlike poles (N–S) attract each other.

✔ Correct Answer: (c) Lodestone

Lodestones are naturally occurring magnets discovered in ancient times. Bar magnets, ring magnets, and U-shaped magnets are all artificial magnets made by humans.

✔ Correct Answer: (d) A magnet

The needle of a magnetic compass is itself a small magnet that can rotate freely. Because it is a magnet, it aligns itself along the North–South direction due to Earth's magnetic field.

✔ Correct Answer: (c) Each piece will have both North and South poles

Poles of a magnet always exist in pairs. No matter how many times a magnet is broken, each piece will always have both a North pole and a South pole. A single pole cannot exist alone.

✔ Correct Answer: (b) Repulsion

Repulsion is the unique identifying property of a magnet. A simple iron bar is attracted by both poles of a magnet, but only a magnet will repel the like pole of another magnet. $\text{Magnet only} \Rightarrow \textbf{Repulsion (like poles)}$

✔ Correct Answer: (c) There is no appreciable change in deflection

The magnetic effect acts through non-magnetic materials like wood, cardboard, plastic, and glass. Placing a piece of wood between the magnet and the compass does not appreciably reduce the magnetic force.

✔ Correct Answer: (d) Copper

Iron, Nickel, and Cobalt are well-known magnetic materials attracted by a magnet. Copper is a non-magnetic material and is not attracted towards a magnet.

Attract; Repel.

Unlike poles (North–South) pull each other together due to attraction, while like poles (North–North or South–South) push each other away due to repulsion. $\text{N–S} \Rightarrow \textbf{Attraction}, \quad \text{N–N or S–S} \Rightarrow \textbf{Repulsion}$

Magnetic materials.

Magnetic materials such as iron, nickel, and cobalt are attracted towards a magnet, whereas materials like wood, plastic, and glass are called non-magnetic materials and are not attracted.

North–South direction.

The compass needle is a small magnet that aligns itself along the North–South direction because Earth behaves like a giant magnet, exerting a magnetic force on the needle.

Two (North and South).

A magnet always has two poles—the North pole and the South pole—which always exist in pairs. It is impossible to obtain a magnet with a single pole.

Lodestones.

Lodestones are naturally occurring magnets found in nature. They were discovered in ancient times and were the basis for the magnets used by sailors in olden days for navigation.

False.

No matter how many times a magnet is broken, each piece will always have both a North pole and a South pole. A single isolated pole (monopole) cannot exist in any piece of a magnet.

True.

Like poles (North–North or South–South) of two magnets always repel each other. This property of repulsion is also used to identify whether a given object is a magnet or just a magnetic material.

False.

Iron filings stick most at the two ends (poles) of a bar magnet, where the magnetic force is strongest. Very few iron filings stick to the middle portion of the magnet.

True.

A freely suspended bar magnet always aligns in the North–South direction because Earth itself behaves like a giant magnet and exerts a magnetic force on the suspended magnet's poles.

True.

As observed in Activity 4.7, placing non-magnetic materials like wood, cardboard, plastic, or glass between a magnet and a compass needle does not appreciably reduce the deflection of the needle, proving that magnetic effects pass through non-magnetic materials.

So the correct pairs are: (i)→(d), (ii)→(a), (iii)→(b), (iv)→(c)

So the correct pairs are: (i)→(b), (ii)→(a), (iii)→(d), (iv)→(c)

The labels 'N' and 'S' in Fig. 4.4 indicate the North pole and South pole of the bar magnet respectively. These are called the poles of the magnet, and maximum iron filings stick at these two ends because the magnetic force is strongest at the poles.

The compass needle shown in Fig. 4.6 is a small magnet mounted on a pin so it can rotate freely. When at rest, it always points in the North–South direction due to Earth's magnetic field, with its red-painted end pointing North.

Magnetic materials are materials that are attracted towards a magnet.

Examples: Iron and Nickel are common magnetic materials. Other examples include cobalt and some combinations of these metals with other materials.

Non-magnetic materials are materials that are not attracted towards a magnet.

Examples: Wood and Glass are non-magnetic materials. Other examples include plastic, rubber, and cardboard, which show no attraction when brought near a magnet.

A magnetic compass is a small circular device that has a magnetised needle mounted on a pin so it can rotate freely, and it comes to rest pointing in the North–South direction.

It is used to find directions at any location, and was historically used by sailors for navigation at sea.

Both poles always exist together and can never be separated.

The three common shapes of magnets are:

1. Bar magnet — long rectangular shape with N and S poles at the two ends.

2. U-shaped (horseshoe) magnet — shaped like the letter 'U' with both poles at the open ends.

3. Ring magnet — circular/ring-shaped magnet with poles on opposite faces.

Each shape is used based on the requirement of the application.

A plain iron bar is attracted by both poles of a magnet, just like a magnet would be. So attraction alone cannot confirm whether an object is a magnet.

However, only a magnet will repel the like pole of another magnet. Therefore, repulsion is the sure test to identify a magnet. $\text{Repulsion} \Rightarrow \textbf{confirms it is a magnet}$

Matsya-yantra (also called machchh-yantra) was an ancient Indian navigation device consisting of a magnetised fish-shaped iron piece kept in a vessel of oil, which aligned itself in the North–South direction.

It is historically significant because it was used by Indians for navigation at sea much before the modern magnetic compass became widespread, showing early knowledge of magnetic properties.

Two important precautions for storing magnets are:

1. Store in pairs with unlike poles on the same side and a piece of wood between them, with soft iron pieces placed across the ends.

2. Do not heat, drop, or hammer a magnet, and keep it away from mobile phones or remote controls, as these can weaken or destroy its magnetism.

Artificial magnets are magnets made by humans from pieces of iron or other magnetic materials, found in laboratories, pencil boxes, stickers, and toys.

Natural magnets (lodestones) occur naturally in the Earth. Artificial magnets can be made in various shapes and sizes as per requirement, whereas lodestones occur only in their natural irregular form.

An iron sewing needle is converted into a magnet by the single-stroke magnetisation method: one pole of a bar magnet is placed at one end of the needle and stroked along its length to the other end, then lifted and returned to the start.

This process is repeated 30–40 times in the same direction, which aligns the magnetic domains in the needle, making it a magnet capable of attracting iron filings.

Method: Tie a thread to the middle of a bar magnet so it hangs horizontally and balanced. Allow it to come to rest — it will always align along the North–South direction. The end pointing North is the North pole; the other end is the South pole.

Principle: The Earth itself behaves like a giant magnet. Its magnetic field exerts a force on the poles of the suspended magnet, rotating it until it aligns with Earth's magnetic North–South direction. $\text{Freely suspended magnet} \Rightarrow \textbf{North–South direction always}$

This principle is used in a magnetic compass for navigation.

Activity (based on Activity 4.7):

1. Place a magnetic compass on a table and let its needle come to rest.

2. Bring a bar magnet near the compass — the needle deflects.

3. Now place a piece of wood between the magnet and the compass (without moving them). Observe the needle.

Observation: The needle shows no appreciable change in deflection.

Conclusion: The magnetic effect passes through non-magnetic materials like wood, cardboard, plastic, and glass. $\text{Magnetic effect} \Rightarrow \text{acts through non-magnetic materials}$

Reshma can use the property of repulsion to identify the magnets:

1. Bring one end of bar A near one end of bar B. If they repel, both are magnets.

2. If they attract, test B with C: if B and C repel, B and C are the magnets; A is plain iron.

3. A plain iron bar is always attracted by a magnet (never repels), while a magnet repels another magnet's like pole.

$\text{Repulsion} \Rightarrow \textbf{Both objects are magnets}$

By testing all pairs systematically, she can identify the two magnets without any extra material.

From Fig. 4.15, positions A and C are near the two poles of the bar magnet, while position B is near the middle of the magnet.

Maximum U-clips will be attracted at positions A and C (the poles), because the magnetic force is strongest at the poles. Very few or no U-clips will be attracted at position B (middle), where the magnetic force is weakest.

$\text{Poles (A, C)} \Rightarrow \textbf{Maximum attraction}; \quad \text{Middle (B)} \Rightarrow \textbf{Minimum attraction}$

This matches option (i): Position A = 10 clips, B = 2 clips, C = 10 clips.

Solution: The mechanic should magnetise the screwdriver by stroking one pole of a bar magnet along the metallic shaft of the screwdriver repeatedly (30–40 times in the same direction). This makes the screwdriver a temporary magnet.

Principle: Steel is a magnetic material. Once the screwdriver is magnetised, it will attract and hold the steel screws at its tip, preventing them from falling. $\text{Magnetised screwdriver} \Rightarrow \textbf{holds steel screws}$

This is a practical application of magnetisation of iron/steel objects.

Experiment: Interaction Between Two Bar Magnets (Activity 4.5)

Materials required: Two bar magnets (A and B) with poles marked, 5–6 round pencils.

Procedure:

1. Place magnet A on top of 5–6 round pencils so it can move freely on a smooth surface.

2. Bring the North pole of magnet B near the North pole of magnet A.

3. Observe the motion of magnet A.

4. Now bring the South pole of magnet B near the North pole of magnet A.

5. Observe again.

6. Repeat using an iron bar in place of one magnet.

Observations:

Conclusions:

$\text{Like poles (N–N or S–S)} \Rightarrow \textbf{Repulsion}$

$\text{Unlike poles (N–S)} \Rightarrow \textbf{Attraction}$

• When an iron bar is used instead of a magnet, it is attracted by both poles — confirming that repulsion is the true test of a magnet.

• A plain iron bar cannot repel a magnet's pole, but a magnet always repels a like pole of another magnet.

This experiment demonstrates the fundamental law of magnetic poles: like poles repel and unlike poles attract.

Poles of a Magnet — Diagram and Explanation

Diagram Instructions:

Draw a long rectangular bar magnet in the centre of the page. Label the left end 'S' (South pole) and the right end 'N' (North pole). Draw curved lines of iron filings clustered thickly at both ends (N and S poles) spreading outward like a brush, with very few filings shown in the middle section. Label: Iron filings (at ends), Bar magnet (centre), N pole (right end), S pole (left end).

Concept of Poles:

• The two ends of a magnet where the magnetic attraction is strongest are called its poles.

• Every magnet has exactly two poles: the North pole (North-seeking pole) and the South pole (South-seeking pole).

• When a bar magnet is placed over iron filings, maximum filings stick at the two poles and very few in the middle.

$\text{Poles} = \text{regions of maximum magnetic force}$

Why a single pole cannot exist:

• If a bar magnet is broken into two pieces, each piece immediately develops its own North and South poles.

• No matter how many times the magnet is broken, every piece — even the tiniest fragment — will always have both poles.

$\text{Broken magnet} \Rightarrow \textbf{Each piece has N and S poles}$

This is a fundamental property of magnets — a magnetic monopole does not exist in nature. This is why magnets are always said to have poles in pairs.

Magnetic Compass — Working and Construction

How a Magnetic Compass Works

A magnetic compass works on the principle that a freely suspended magnet always aligns in the North–South direction due to Earth's magnetic field. Earth behaves like a giant magnet, and the compass needle (which is a small magnet) responds to this field.

$\text{Earth's magnetic field} \Rightarrow \textbf{Compass needle aligns N–S}$

Structure of a standard compass (Fig. 4.6):

• A small circular box with a transparent cover.

• A magnetised needle balanced on a central pin so it rotates freely.

• A dial with directions (N, NE, E, SE, S, SW, W, NW) marked below the needle.

• The North-pointing end of the needle is usually painted red.

Using a compass:

1. Place compass on a flat surface — needle comes to rest pointing N–S.

2. Rotate the box until N on the dial aligns with the needle.

3. All directions at that location are now indicated.

Making a Simple Compass (Activity 4.4)

Materials: Iron sewing needle, bar magnet, cork, glass bowl, water.

Steps:

1. Place the needle on a wooden table. Stroke one pole of the bar magnet along the needle from one end to the other, 30–40 times in the same direction — this magnetises the needle.

2. Test: Bring iron filings near the needle — if attracted, it is magnetised.

3. Pass the magnetised needle horizontally through a cork.

4. Float the cork in a glass bowl filled with water.

5. Allow to settle — the needle aligns in the North–South direction. Your compass is ready!

Diagram Instructions:

Draw a glass bowl filled with water. On the water surface, draw a circular cork with a needle passing through it horizontally. Label: Bowl, Water, Cork, Magnetised needle, N (one end), S (other end).

Historical note: A similar device called the matsya-yantra was used by ancient Indians — a magnetised fish-shaped iron piece in a vessel of oil — for navigation at sea.

Ring Magnets X and Y — Levitation and Poles

Reason for Levitation (Fig. 4.16)

Magnet X floats above magnet Y without touching it because the like poles of the two ring magnets are facing each other.

$\text{Like poles (same face facing)} \Rightarrow \textbf{Repulsion}$

The repulsive force between like poles pushes magnet X upward, counteracting gravity. This results in magnet X appearing to levitate above magnet Y on the rod.

How to Bring X in Contact with Y

To bring magnet X in contact with magnet Y without pushing either magnet, simply flip (turn over) magnet X so that its opposite pole now faces magnet Y. This changes the interaction from like poles (repulsion) to unlike poles (attraction), and magnet X will move down towards magnet Y.

$\text{Flip X} \Rightarrow \text{Unlike poles face each other} \Rightarrow \textbf{Attraction} \Rightarrow \text{X moves down}$

Concept of Attraction and Repulsion

Key Rules:

$\text{Like poles} \Rightarrow \textbf{Repel each other}$

$\text{Unlike poles} \Rightarrow \textbf{Attract each other}$

Practical application: This principle of repulsion between like poles is used in Maglev trains, where the train levitates above the track due to magnetic repulsion, reducing friction and allowing very high speeds. The hopping frog toy (Fig. 4.18) also works on the same principle of alternating poles of ring magnets.

Classification of Magnetic and Non-Magnetic Materials

Classification Table

$\text{Magnetic materials} = \{\text{Iron, Nickel, Cobalt, Steel}\}$

$\text{Non-magnetic materials} = \{\text{Wood, Plastic, Glass, Rubber}\}$

Key Difference

• Magnetic materials: Contain iron, nickel, or cobalt — attracted by a magnet due to alignment of their internal magnetic domains.

• Non-magnetic materials: Do not contain magnetic metals — their internal structure does not respond to a magnetic field.

Importance in Everyday Life

This classification is very useful in practical situations:

Application 1 — Separating materials:

In recycling plants, a large electromagnet is used to separate iron and steel scraps from non-magnetic waste like plastic and glass. This is possible only because of the difference between magnetic and non-magnetic materials.

Application 2 — Magnetic compass and navigation:

The compass needle is made of steel (a magnetic material) so it responds to Earth's magnetic field and points North. The compass box is made of non-magnetic plastic or glass so it does not interfere with the needle's alignment.

$\text{Magnetic needle} + \text{Non-magnetic casing} \Rightarrow \textbf{Accurate compass}$

Fun fact: The activity of using a magnet to retrieve a steel paperclip from water (Fig. 4.13) works because steel is magnetic — the magnetic effect passes through the non-magnetic water to attract the clip.