An ammeter has a resistance of $50 Ω$ and a full scale deflection current of 50 $μ A$ . It can be used a voltmeter or as a higher range ammeter provided that a resistance is added to it. Choose the correct range and resistance combination from the following

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1 mA range with $50 Ω$ resistance in parallel

0.1 mA range with $50 Ω$ resistance in parallel

20 V range with approximately $400 k Ω$ resistance in series

100 V range with approximately resistance in series

answer is A, B, D.

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Detailed Solution

For ammeter,
$i = \frac{i_{\max} (R_{s} + R_{A})}{(R_{s})}$
$\Rightarrow i = 0.1 m A$ for $R_{s} = 50 Ω$ [as $R_{A} = 50 Ω$ and $i_{\max} = 50 μ A$ ]
For voltmeter,
$V = i_{\max} (R_{A} + R_{V})$
$\Rightarrow V \approx 10 V$ for $R_{V} = 200 k Ω$