Question

1. Magnetic field (B) exerts a torque on a magnetic moment (m) (such as a magnet bar) to align the magnetic moment along the B- field direction. In genreal, the vector torque is defined as: t=mxB, with a magnitude of , where $\Theta$ is the angle between m and B as shown in figure 1. However, in Eq. (1) the magnitude of t is defined as $\tau =-mBsin\Theta$ . What does the minus sign mean?

T = ITI = mBsinΘ

Answer 1

Given that Magnetic Field B exerts torque on magnetic moment m Magnetic moment m aligns in Magnetic Field, B -field direction Torque is cross-product of m andB Magnitude of torque is given by τ_m1B sin θ Where 6 is the angle between m and B Direction of the torque vector determines the sign. If the torque causes the rotation in clockwise direction, it is negative If the torque causes the rotation in counter-clockwise direction, it is positive Since it is given that in Eq. (1) that t means that Direction of rotation is in clockwise direction