In the circuit shown the resistance of voltmeter is $10,000\, ohm$ and that of ammeter is $20\,ohm$. The ammeter reading is $0.10\,Amp$ and voltmeter reading is $12$ $\mathrm{volt}.$ Then $R$ is equal to .............. $\Omega$
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$\mathrm{V}=\mathrm{i}(\mathrm{r}+\mathrm{R})$
$12=0.1(20+r) \Rightarrow r=100 \Omega$
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