A coil 4.20 cm radius, containing 500 turns, is placed in a uniform magnetic field that varies with time according to B=( 1.20×10−2 T/s )t+( 2.60×10−5 T/s4 )t4. The coil is connected to a 640-Ω resistor, and its plane is perpendicular to the magnetic field. You can ignore the resistance of the coil.

a)Find the magnitude of the induced emf in the coil as a function of time.