A very long, straight solenoid with a cross-sectional area of 6.00cm2 is wound with 40.0 turns of wire per centimeter, and the windings carry a current of 0.250A . A secondary winding of 2.00 turns encircles the solenoid at its center. When the primary circuit is opened, the magnetic field of the solenoid becomes zero in 5.00×10?2s .
What is the average induced emf in the secondary coil?