In Section 21.8, we mentioned that an emf is induced in a distant coil or current loop via an electromagnetic wave. For the case in Figure 21.32, this electromagnetic wave travels from the inner solenoid to the outer loop. In a vacuum, this wave travels at a speed c = 3.00x10⁸ m/s. Calculate the time Δt it takes this wave to travel a distance of 1.0 mm as might be typical in an electric circuit containing several inductors. Your result for Δt should show that in this case the induced emf appears nearly instantaneously.

 

There is a flux through the outer loop even though B at the loop is zero.