1.

When the value of R in the balanced Wheatstone bridge, shown in the figure, is increased from 5 Omega to 7 Omega, the value of S has to be increased by 3 Omega in order to maintain the balance. What is the initial value of S?

Answer»

`2.5 Omega`
`3 Omega`
`5 Omega`
`7.5 Omega`

Solution :FROMTHE balancedcondition ofwheatstonebridge, we canwritethat ` P/Q = R /S `
sinceP and Qhasconstantvalue
` thereforeP/Q =`constant`IMPLIES R/5 ` = constant
Nowas perthe questiongivenin orderto maintainthe balance
` R/S = 5/S`( initially ) and
` R/S=(7 )/((S +3))`(finally )
comparingeqn(i ) and (ii)
` therefore(5)/S(S )= (7 )/((S +3)) implies 5 (S+3) = 7 S`
` implies5S+ 15 = 7S implies 7S-5S =15`
`implies2S= 15 impliess=(15)/(2) = 7.5Omega `


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