QJEEAdv14Ph1a35: JEE Advanced 2014 Physics - Class 12 JEEAdv14Ph1a35 Solution: A galvanometer gives full scale deflection with 0.006 A…

Question

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A galvanometer gives full scale deflection with 0.006 A current. By connecting it to a 4990

\Omega

resistance, it can be converted into a voltmeter of range 0-30V. If connected to a

{{2n} \over {249}}\Omega

resistance, it becomes an ammeter of range 0-1.5 A. The value of n is

Accepted Answer

{i_g}(G + 4990) = V

\Rightarrow {6 \over {1000}}(G + 4990) = 30

\Rightarrow G + 4990 = {{30,000} \over 6} = 5000

\Rightarrow G = 10\,\Omega

{V_{ab}} = {V_{cd}}

\Rightarrow {i_g}G = (1.5 - {i_g})S

\Rightarrow {6 \over {1000}} \times 10 = \left( {1.5 - {6 \over {1000}}} \right)S

\Rightarrow S = {{60} \over {1494}} = {{2n} \over {249}}

\Rightarrow n = {{249 \times 30} \over {1494}} = {{2490} \over {498}} = 5

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