In a potentiometer experiment the following circuit arrangement is used. AB is the potentiometer wire.
![](https://www.sarthaks.com/?qa=blob&qa_blobid=8440633743188908682)
When the key K1 is closed (K2 open), the balancing length is found to be l . When the key K2 is closed (K1 open), the balancing length is found to be 2l . The value of r, in terms of R1 and R2 , is
(1) \(\frac{R_1R_2}{R_2-R_1}\)
(2) \(\frac{2R_1R_2}{R_2-R_1}\)
(3) \(\frac{R_1R_2}{R_2-2R_1}\)
(4) \(\frac{2R_1R_2}{R_2-2R_1}\)