Solution: The flux density inside the solenoid is constant and may be calculated using Ampere’s law. The electromotive
force is calculated using the notation in Figure 10.7b and the transformer action emf in Eq. (10.1). In (b), the current is limited
only by the internal resistance of the loop, whereas in (c), the power dissipated multiplied by time gives the required energy:
(a) The magnetic flux density in the solenoid is calculated using a contour as shown in Figure 10.10a. The total current
enclosed by the contour is wnI and the magnetic flux density is zero outside the solenoid: