Saved Bookmarks
| 1. |
What is Wheatstonc hridge ? Explain its principle. |
Answer» Solution :`rArr`Wheatstone bridge is special network of four resistors and BATTERY connected as shown in figure below.  `rArr` Four resistors `R_(1) , R_(2) , R_(3) and R_(4)` are connected with battery as shown in figure. `rArr` Battery is connected between A and C called battery arm. `rArr` Galvanometer is connected between B and D hence, it is called galvanometer arm. `rArr` Consider battery is to be ideal (zero internal resistance). `rArr`Current flowing in resistor `R_(1), R_(2), R_(3) and R_(4)` be `I_(1), I_(2), I_(3) and I_(4)`respectively. `rArr` Current will be flowing through all four resistors and galvanometer. In special condition when current through galvanometer is zero (lg = 0) Wheatstone bridge is said to be in balanced condition. `rArr` In balanced condition of Wheatstone bridge `I_(1) = I_(3) and I_(2) = I_(4)` . `rArr` By USING Kirchhoff.s second LAW for LOOP ABDA. `-I_(1) R_(1) + 0 + I_(2) R_(2) = 0 "" [ because I_(g) = 0 ] ` `thereforeI_(1) R_(1) = I_(2) R_(2) "" `... (1) Similarly for loop BCDB, `I_(4) R_(4) + 0 - I_(3) R_(3) = 0` by substituting `I_(3) = I_(1) and I_(4) = I_(2)` `I_(2) R_(4) - I_(1) R_(3) = 0` `therefore I_(1) R_(3) = I_(2) R_(4) ""` ... (2) Comparing equation (1) and (2) , `(R_(1))/(R_(3))= (R_(2))/(R_(4))` `therefore (R_(1))/(R_(2)) = (R_(3))/(R_(4)) " or " (R_(2))/(R_(1)) = (R_(4))/(R_(3))` `rArr` This equation represent principle of Wheatstone bridge which is condition for balance of Wheatstone bridge. `rArr` As an application of Wheatstone bridge value of `R_(1), R_(2), R_(3)` are known and `R_(4)` is unknown then, `R_(4) = R_(3) xx (R_(2))/(R_(1))` will give value of unknown resistor `R_(4)`. |
|