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Page 493 | Volume 2 | Chapter 27 | Testing and Testing Apparatus

Ques. How is it known whether too much or too little resistance be unplugged?

Ans. The galvanometer needle will be deflected to one side for too much resistance, and to the opposite side for too little resistance.

Fig. 569. - Method of reversing arms of Wheatstone bridge with reversing blocks.
Fig. 569.—Method of reversing arms of Wheatstone bridge with reversing blocks. The arrangement shown in the figure is classical, being that used in the English post office type of Wheatstone bridge. It is open to the objections which apply to the use of several plugs, one of which is withdrawn to obtain the desired resistance.

Ques. What is the meaning of "Inf.," marked on the bridge?

Ans. It stands for "infinity," because the resistance coil at the point marked infinity is omitted so that adjacent sections of the arm are disconnected when the plug is taken out.

In fact, the air gap interposed by the removal of the plug by no means provides an infinitely great resistance, but is usually called such because it is vastly greater than any of the other resistances of the bridge.


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