| In a meter bridge experiment resistances are connected as shown in the figure. Initially resistance \[P=4\,\Omega \] and the neutral point N is at 60 cm from A. Now an unknown resistance R is connected in series to P and the new position of the neutral point is at 80 cm from A. The value of unknown resistance R is - [JEE Online 09-04-2017] |
 |
A) \[\frac{33}{5}\Omega \]
B) \[5\,\Omega \]
C) \[\frac{20}{3}\Omega \]
D) \[7\,\,\Omega \]
Correct Answer: C
Solution :
| [c] Initially \[\frac{4}{60}\,=\frac{Q}{40}\,\] \[Q=\frac{16}{6}=\frac{8}{3}\Omega \] |
| Finally |
| \[\frac{4+R}{80}=\frac{Q}{20}=\frac{8}{60}\] |
| \[4+R=\frac{64}{6}\] |
| \[R=\frac{64}{6}-4\,=\frac{64-24}{6}=\frac{40}{6}\] |
| \[=\frac{20}{3}\Omega \] |
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