Question

The torque acting on a magnetic dipole placed in uniform magnetic field is zero, when the angle between the dipole axis and the magnetic field is _____.

• A. 45°
• B. 60°
• C. 90°
• D. zero

Answer 1

The Correct Option is D

Step 1: Recall the expression for torque (\( \tau \)) acting on a magnetic dipole (\( M \)) placed in a uniform magnetic field (\( B \)):

\[ \tau = MB \sin\theta \] 

where \( \theta \) is the angle between the magnetic dipole axis and the direction of the magnetic field.

Step 2: Determine when torque is zero.

The torque will be zero if:

\[ \tau = MB \sin\theta = 0 \]

This occurs when:

\[ \sin\theta = 0 \quad \Rightarrow \quad \theta = 0^\circ \text{ or } 180^\circ \]

Step 3: From the given options, angle \(0^\circ\) satisfies the above condition.

Final Conclusion:
The torque on the magnetic dipole is zero when the angle between the dipole axis and the magnetic field is zero degrees (0°).

Answer 2

The torque \( \tau \) on a magnetic dipole in a uniform magnetic field is given by the formula: \[ \tau = m B \sin(\theta) \] where:
\( m \) is the magnetic moment of the dipole,
\( B \) is the magnetic field strength,
\( \theta \) is the angle between the magnetic moment and the magnetic field.

When \( \theta = 0^\circ \) (i.e., the dipole axis is aligned with the magnetic field), \( \sin(0^\circ) = 0 \). Thus, the torque acting on the dipole is zero.

Therefore, the correct answer is zero.