In the case of a dynamo, an inductor may be either a copper wire or copper bar.
Ques. How may a conducting circuit be moved across a magnetic field without having a current induced therein?
Ans. If a conducting circuit—a wire ring or single coil, for example—be moved in a uniform magnetic field, as shown in fig. 127, so that only the same number of lines of force pass through it, no current will be generated, for since the coil is moved by a motion of translation to another part of the field, as many lines of force will be left behind as are gained in advancing from its first to its second position.
Ques. Describe another movement by which no current will be induced.
Ans. If the coil be merely rotated on itself around a central axis, that is, like a fly wheel rotating around a shaft, the number of lines of force passing through the coil will not be altered, hence no current will be generated.
Ques. State the essential condition for current induction in a uniform field.
Ans. The coil in which a current is to be induced, must be tilted in its motion across the uniform field, or rotated around any axis in its plane as in fig. 128, so as to alter the number of lines of force which pass through it.
Ques. In what direction will the current flow in the coil, fig. 128?