Question

A bar magnet of magnetic moment 5.0 A m² has poles 20 cm apart. The pole strength would be

• A. 20 A m
• B. 30 A m
• C. 1 A m
• D. 25 A m

Hint:

Pay close attention to units. The magnetic moment is in Ampere-meter squared (A m²), while pole strength is in Ampere-meter (A m). The distance must be in meters to ensure consistency. Always convert cm to m before calculating.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
This problem relates the magnetic moment of a bar magnet to its pole strength and magnetic length. The magnetic moment is a vector quantity that represents the overall magnetic strength and orientation of a magnet.

Step 2: Key Formula or Approach:
The magnetic moment (\(M\)) of a bar magnet is defined as the product of its pole strength (\(m\)) and its magnetic length (\(2l\)). \[ M = m \times (2l) \] The magnetic length (\(2l\)) is the distance between the two poles of the magnet.

Step 3: Detailed Explanation:
Given data:
Magnetic moment, \(M = 5.0 \, \text{A m}^2\).
Distance between poles (magnetic length), \(2l = 20 \, \text{cm} = 0.20 \, \text{m}\).
Calculation:
We need to find the pole strength \(m\). Rearranging the formula: \[ m = \frac{M}{2l} \] Substitute the given values: \[ m = \frac{5.0 \, \text{A m}^2}{0.20 \, \text{m}} \] \[ m = \frac{5}{0.2} = \frac{50}{2} = 25 \, \text{A m} \]

Step 4: Final Answer:
The pole strength of the bar magnet would be 25 A m.