Q109 / 120 · VITEEE 2007 · Physics

A rectangular coil ABCD which is rotated at a constant angular velocity about an horizontal as shown in the figure. The axis of rotation of the coil as well as the magnetic field $\mathrm{B}$ are horizontal. Maximum current will flow in the circuit when the plane of the coil is Figure

  • A
    inclined at 30 degrees to the magnetic field
  • B
    perpendicular to the magnetic field
  • C
    inclined at 45 degrees to the magnetic field
  • Correct answer
    D
    parallel to the magnetic field

Solution

Torque on the coil is $\tau=\mathrm{nIB} \mathrm{A} \cos \theta$. If coil is set with its plane parallel to direction of magnetic field B, then $\theta=0^{\circ}, \cos \theta=1$ $\Rightarrow \tau=n I B A .1=n I B A=m a x i m u m$ Hence, $\mathrm{I}=$ maximum $($ as $\mathrm{n}, \mathrm{B}, \mathrm{A}$ are constant $)$

Hence, the correct answer is option: 'D'.

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