CBSE Class 12-science Answered
what is meant by a post office box? and menntion its proper uses.
Asked by Sagar krishna | 16 May, 2014, 07:33: PM
Expert Answer
A Post Office Box is used to measure an unknown resistance. It is a Wheatstone bridge with three arms P, Q and R ; while the fourth arm(S) is the unknown resistance.
P and Q are known as the ratio arms while R is known as the rheostat arm.
At balance The current flowing through galvanometer (G) is zero and the unknown resistance S is calculated using the formula
S = (P/Q) R
Answered by Ravindra Kapal | 20 May, 2014, 05:46: PM
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