Ques. What happens when the loop is rotated?
Ans. According to the law of electromagnetic induction, when the loop is rotated around its horizontal axis in the direction indicated by the curved arrow, an electromotive force will be induced in the loop, the magnitude of which depends on the rate of change of the number of lines of force threading through, or embraced by the loop.
That is, if the number of lines embraced by the loop be increased from, say, 0 to 1000, or decreased from 1000 to 0, in one second, the electromotive force generated will be two times as great as if the increase or decrease were only 500 lines per second.
Ques. Upon what does the direction of the induced current depend?
Ans. Upon the direction of the lines of force and direction of rotation of the loop.
Ques. How is Fleming’s rule applied to determine the direction of current?
Ans. In applying this rule, the horizontal portion of the loop, such as A B or C D (fig. 165), is to be considered as moving up or down; that is, the component of its motion at right angles to the lines of force is taken as the direction of motion. When the loop is in the position A B C D, such that its plane is vertical or perpendicular to the lines of force, the maximum number of magnetic lines thread through it, but when it is in a horizontal position, A′ B′ C′ D′, so that its plane is parallel to the lines of force, no lines pass through the loop. During the rotation from position A B C D to A′ B′ C′ D′, the number of lines passing through the loop is reduced from the maximum to zero, the reduction taking place with increasing rapidity as the loop approaches the horizontal position, the electromotive force thus induced increasing in like proportion. Continuing the rotation from the horizontal position A′ B′ C′ D′ to the inverted vertical position A B C D (fig. 166), the number of lines passing through the loop is increased from zero to the maximum, the increase taking place with decreasing rapidity as the loop approaches the inverted vertical position, the electromotive force thus induced decreasing in like proportion.
Ques. How does the current flow during the first half of the revolution of the loop?