# NEET Physics Magnetism and Matter Questions Solved

NEET - 2016

A bar magnet is hung by a thin cotton thread in a uniform horizontal magnetic field and is in equilibrium state. The energy required to rotate it by ${60}^{\circ }$ is W. Now the torque required to keep the magnet in this new position is

(a) $\frac{W}{\sqrt{3}}$                    (b) $\sqrt{3}W$

(c) $\frac{\sqrt{3}W}{2}$                (d) $\frac{2W}{\sqrt{3}}$

Concept Videos :-

#3 | Magnetic Dipole Moment & Field due to Bar Magnet
#4 | Superposition of Magnetic Field due to Bar Magnet
#5 | Field due to Short Bar Magnet
#6 | Torque Acting on Bar Magnet in Uniform Field
#7 | Work Done in Rotating Dipole in Field & PE
#8 | Oscillations of Bar Magnet in Uniform Field
#9 | Solenoid as Equivalent Bar Magnet

Concept Questions :-

Bar magnet

(b)$\because$ Work done is rotating the magnet

Where, M= magnetic moment of the magnet

B = Magnetic field

W $=\left(1-\frac{1}{2}\right)⇒\frac{MB}{2}$

...(i)

Torque on a magnet in this position is given by,

[from Eq. (i)]

$=2W\frac{\sqrt{3}}{2}=W\sqrt{3}$

Difficulty Level:

• 8%
• 60%
• 25%
• 9%
Crack NEET with Online Course - Free Trial (Offer Valid Till September 22, 2019)