[Illustration: FIG. 165.--Simple elementary alternator. Its parts are a single conducting loop, A B C D, placed between the poles of a permanent magnet, and having its ends connected with a ring, F, and shaft, G, upon which bear brushes M and S, connected with the external circuit. When the loop is rotated clockwise the induced current will flow in the direction indicated by the arrows during the first half of the revolution.] 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?= Ans. It flows in the direction A B C D (fig. 165), as is easily ascertained by aid of Fleming’s rule. [Illustration: FIG. 166.--Simple elementary alternator, showing reversal of current when the loop has made one half revolution from the position of fig. 165. It should be noted that A B, for instance, which has been moving _downward_ during the first half of the revolution (fig. 165), moves _upward_ during the second half (fig. 166); hence, the current during the latter interval flows in the opposite direction.] =Ques. What is the path of the current to the external circuit?= Ans. It flows out through brush M (fig. 165) and returns through brush S, thus making M positive and S negative.