A bar magnet is cut into two equal halves by a plane parallel to the magnetic axis of the following physical quantities the one which remains unchanged is

Options

A. Pole strengths
B. Magnetic moment
C. Intensity of magnetization
D. Moment of inertia

Answer

To solve the question, we need to analyze the effects of cutting a bar magnet into two equal halves along a plane parallel to its magnetic axis. Let's break down the solution step by step:

### Step 1: Understand the Structure of a Bar Magnet
A bar magnet has two poles: a north pole and a south pole. The magnetic moment (M) of the magnet is a vector quantity that represents the strength and direction of the magnet's magnetic field.

### Step 2: Cutting the Bar Magnet
When the bar magnet is cut into two equal halves along a plane parallel to the magnetic axis, each half will still retain some magnetic properties. However, certain physical quantities will change due to the alteration in dimensions.

### Step 3: Identify the Physical Quantities
The physical quantities we need to consider include:
- Pole strength (p)
- Magnetic moment (M)
- Intensity of magnetization (I)
- Moment of inertia (I)

### Step 4: Analyze the Changes
1. **Pole Strength (p)**: When the magnet is cut, each half will have half the pole strength of the original magnet. Thus, pole strength changes.

2. **Magnetic Moment (M)**: The magnetic moment is given by the product of pole strength and the length of the magnet (M = p × l). Since both the pole strength and the length of each half are halved, the magnetic moment will also change.

3. **Moment of Inertia (I)**: The moment of inertia depends on the mass distribution of the magnet. When cut, the mass of each half is reduced, which will also change the moment of inertia.

4. **Intensity of Magnetization (I)**: Intensity of magnetization is defined as the magnetic moment per unit volume (I = M/V). Since the volume of each half is halved but the magnetic moment also changes in a way that keeps the ratio constant, the intensity of magnetization remains unchanged.

### Conclusion
After analyzing the changes in the physical quantities, we find that the only quantity that remains unchanged when a bar magnet is cut into two equal halves is the **Intensity of Magnetization (I)**.

### Final Answer
The physical quantity that remains unchanged is **Intensity of Magnetization (I)**.

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