In which case is there an induced electromotive force?
a. a permanent bar magnet is held inside a coil of wire
b. field line's from earths magnetic field cross the area of a coil of wire
c. an electromagnet operating on direct current is held a second coil of wire
d. an electromagnet operating on alternating current is held inside a second coil of wire

The space within which a test north pole experiences a force magnetic poles 2. a powerful stream of electrons flowing high above the earth in the ionosphere electrojet 3. a concept to explain the directional nature of a magnetic field field lines 4. coil of wire designed to produce a magnetic field by a current passing through its windings ionosphere 5. that region above the earth's atmosphere where particles exist in an ionized state magnetic field 6. the extremities of a magnet where the field lines tend to converge or concentrate aurora borealis 7. a phenomenon that occurs in the northern latitudes; the northern lights solenoid