# Describe average emf in a rotating coil

Publish On: 2019-04-24

Total Post: 819

# lala singh

Total Post: 22

## ANS: Describe average emf in a rotating coil

An important case of induced emf is that in which a coil rotates at a uniform angular velocity in a uniform magnetic field. A magnetic field that is parallel to the plane of the paper. The axis of rotation O is perpendicular to the plane of the axis of rotation. As the coil rotates in the field, it “cuts” flux at a variable rate, since only the motion perpendicular to the field is effective in producing an induced emf. When the coil is at position GH, the plane of the coil is perpendicular to the field and the conductors C and D are moving parallel to the field at position JK, the conductors are moving normal to the field and the induced emf is a maximum.

If the coil rotates through an angle of 90° from the position GH to JK, the change of flux in the coil will be BA, all of the flux linked by the area of the coil. Hence the average emf is

Where A is the area of the coil and t is the sum time required for a quarter revolutions. It must be clearly noted that this average emf is not one-half the maximum emf, since the emf does not vary linearly.