Which one of the following statements about bar magnet is correct?
When a piece of a bar magnet is bisected perpendicular to its axis, two new bar magnets are formed.
Understanding Bar Magnet Properties
A bar magnet is a permanent magnet with two poles, traditionally called the North pole and the South pole. These poles are located near the ends of the magnet. A fundamental property of magnets is that magnetic poles always exist in pairs. Isolated magnetic poles, known as magnetic monopoles, have not been observed.
Analyzing Statements About Bar Magnets
Let's examine each statement provided in the options to determine which one correctly describes a property of a bar magnet.
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Statement 1: The pole strength of the north-pole of a bar magnet is larger than that of the south-pole.
This statement is incorrect. For any magnet, the strength of the North pole is always equal in magnitude to the strength of the South pole. They are opposite in nature (one attracts, the other repels in a specific direction), but their strengths are equal.
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Statement 2: When a piece of a bar magnet is bisected perpendicular to its axis, the north and south poles get separated.
This statement is incorrect. As mentioned earlier, magnetic poles always exist in pairs. When a magnet is cut, new poles are induced at the cut surfaces. You cannot isolate a North pole from a South pole by simply cutting a magnet.
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Statement 3: When a piece of a bar magnet is bisected perpendicular to its axis, two new bar magnets are formed.
This statement is correct. When a bar magnet is cut into two or more pieces, each piece behaves as a complete new magnet. Each new piece will have its own North pole and South pole. This is because the magnetic property is inherent in the material's structure, and cutting the magnet doesn't eliminate the paired nature of the poles.
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Statement 4: The poles of a bar magnet are unequal in magnitude and opposite in nature.
This statement is incorrect. The poles of a bar magnet are equal in magnitude but opposite in nature. 'Opposite in nature' refers to the fact that a North pole attracts a South pole but repels another North pole, and vice versa.
Summary of Bar Magnet Properties
Based on the analysis, the correct statement is the one describing what happens when a bar magnet is cut perpendicular to its axis.
| Statement | Correctness | Explanation |
|---|---|---|
| Pole strength comparison (North vs South) | Incorrect | Pole strengths are equal in magnitude. |
| Pole separation upon cutting | Incorrect | Poles always exist in pairs; new poles are induced. |
| Formation of new magnets upon cutting | Correct | Each piece forms a new complete magnet. |
| Pole magnitude and nature | Incorrect | Poles are equal in magnitude and opposite in nature. |
Therefore, when a bar magnet is cut perpendicular to its axis, two new bar magnets are formed, each with its own North and South pole.
Revision Table: Key Concepts of Bar Magnets
| Concept | Description |
|---|---|
| Magnetic Poles | Points near the ends of a magnet where the magnetic field is strongest (North and South). |
| Pole Strength | A measure of the force exerted by a magnetic pole. North and South poles of a magnet have equal strength. |
| Law of Poles | Like poles repel each other, and unlike poles attract each other. |
| Magnetic Monopole | A hypothetical isolated magnetic pole (either North or South) which has not been observed in nature. |
| Cutting a Magnet | When a magnet is cut, each piece becomes a new magnet with its own North and South poles. You cannot isolate a single pole. |
Additional Information: Magnetic Fields and Cutting Magnets
Magnetic field lines are a way to visualize the magnetic field around a magnet. These lines originate from the North pole and terminate at the South pole, forming continuous closed loops within the magnet's material.
When you cut a bar magnet perpendicular to its axis, you are essentially interrupting these internal magnetic field lines. At the newly created surfaces, the field lines emerge from one surface (acting as a new North pole) and enter the other (acting as a new South pole), effectively forming new magnetic poles on each piece.
This phenomenon reinforces the idea that magnetic poles always come in pairs ($\text{N-S}$). You cannot have a North pole without a corresponding South pole, regardless of how many times you divide the magnet. The smallest possible magnetic entity still retains this dipole nature, although at the atomic level, magnetism arises from the alignment of electron spins (creating tiny magnetic dipoles).
The magnetic dipole moment of a magnet can be represented by the vector $\vec{m}$. When a magnet is cut, the total magnetic dipole moment of the original magnet is the vector sum of the dipole moments of the resulting pieces.
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