Question

Evelyn wears glasses whose wire frames are shaped like to circles, each with an area of 7.0x10^-4 m^2. The horizontal component of the earths' magnetic field in Evelyn's hometown is 4.9x10^-5 T. If Evelyn turns her head back and forth, rotating it through 90degrees every 0.5s, what is the induced voltage in the wire frame of one eyepiece?