Question

The axial field \( B_A \) and equatorial field \( B_E \) due to a short bar magnet at equal distances are related as:

• A. \( B_A = 2 B_E \)
• B. \( B_A = -2 B_E \)
• C. \( B_A = -B_E \)
• D. \( B_A = -2\pi B_E \)

Hint:

The axial field is double the equatorial field but opposite in direction.

Answer 1

The Correct Option is B

For a short bar magnet:
\( B_A = \frac{\mu_0}{4\pi} \cdot \frac{2M}{r^3} \), \quad \( B_E = \frac{\mu_0}{4\pi} \cdot \frac{M}{r^3} \)
But directionally, \( B_E \) is opposite to \( B_A \), so:
\( B_A = -2 B_E \)