A tightly wound solenoid with n turns per unit length and cross sectional area A is bent

Question:

A tightly wound solenoid with n turns per unit length and cross sectional area A is bent into a flexible torus. Two external leads let the current flow in and out. Find the EMF that appears across the leads when a slowly varying, time-dependent current I(t) flows through the hole in the torus as shown below. Conversely, show that no EMF arises from a time-dependent current that does not flow through the hole.