question_answer

                In metre-bridge the balancing length from left is found to be 20 cm when standard resistance of \[1\Omega \] is in right gap. The value of unknown resistance is:                                                                                     

A)                 \[0.25\,\,\Omega \]       

B)                 \[0.4\,\,\Omega \]         

C)                 \[0.5\,\,\Omega \]         

D)                 \[4\,\,\Omega \]

Correct Answer: A

Solution :

                Let unknown resistance be X.                                 Then condition of Wheatstone's bridge gives,                 \[\frac{X}{R}=\frac{20\,r}{80\,r}\]                 Hence, unknown resistance is                 \[X=\frac{20}{80}\times R=\frac{1}{4}\times 1(\because \,R=1\,\Omega )\]                 \[=0.25\,\Omega \]