A 100 turn closely wound circular coil of radius 10 cm carries a current of 3.2 A. The coil is placed in a vertical plane and is free to rotate about a horizontal axis that coincides with its diameter. A uniform magnetic field of 2T in the horizontal direction exists such that initially, the axis of the coil is in the direction of the field. The coil rotates through an angle of 90° under the influence of the magnetic field. What is the difference of magnitude of the torque on the coil in the initial and final position?
$1. 0$
$2. 10 N-m$
$3. 20 N-m$
$4. 15 N-m$

A 100 turn closely wound circular coil of radius 10 cm carries a current of 3.2 A. What is the angular speed acquired by the coil when it has rotated by 90° under the influence of a magnetic field of magnitude 2T that is applied along the axis of the coil? The moment of inertia of the coil is 0.1 kg-$m^2$.

$1.\mathrm{ 10} s^{-1}$
$2.\mathrm{ 30} s^{-1}$
$3.\mathrm{ 40} s^{-1}$
$4.\mathrm{ 20} s^{-1}$

Which one of the following statements is incorrect?