Q144 / 180 · JIPMER 2015 · Physics

The galvanometer resistance is $30 \Omega$ and it is connected to 2 V battery along with a resistance $2000 \Omega$ in series. A full scale deflection of 25 divisions is obtained. In order to reduce this deflection to 20 divisions, the resistance in series should be

  • Correct answer
    A
    $2470 \Omega$
  • B
    $2320 \Omega$
  • C
    $2180 \Omega$
  • D
    $2210 \Omega$

Solution

Total initial resistance $=G+R=30+2000=2030 \Omega$ Current $\quad i=\frac{2}{2030} \mathrm{~A}$ Let $x$ be the effective resistance of the circuit, then $\begin{aligned} 2 V & =2030 \times \frac{2}{2030} \times 10^3 \\ & =x \times \frac{2}{2.5} \\ \Rightarrow \quad x & =\frac{2 \times 2.5}{2} \times 10^3 \\ & =2500 \Omega\end{aligned}$ $\therefore$ Resistance to be added $=2500-30=2470 \Omega$

Hence, the correct answer is option: 'A'.

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