A coil is rotated in a uniform magnetic field about an axis perpendicular to the field. The emf induced in the coil would be maximum when the plane of the coil is:

Explanation

According to Faraday's law when magnetic flux linking a circuit changes, an electromotive force is induced in the circuit proportional to the rate of change of flux linkage. So, when a coil is rotated in the uniform magnetic field about an axis passing through the center and perpendicular to the direction of the field then emf: emf= -dՓ/dt ՓB =BAcos𝝷 =-d(BAcos𝝷)/dt =-BA d/dt cos𝝷 = -BA =sin d𝝷/dt = emf= BAsin d𝝷/dt Hence emf↑ when sin𝝷 ↑ Sin𝝷 = max when𝝷 =𝞹 /2 B⟂A when plane ∥ B i.e. angle between the area vector and the magnetic field is π/2 so the angle between the plane of the coil and magnetic field is zero or the induced emf in the coil is maximum when cosθ is maximum or θ is zero means when the plane of the coil is parallel to the field as shown below. Note; If it is perpendicular then no emf would be induced and at 450 it would not be maximum.