In the circuit shown in the figure, no current flows through the ideal ammeter. If the internal resistance of the cell is negligible, the value of unknown resistance $R $ is .............. $\Omega$
A$5 $
B$8$
C$10 $
D
None of these.
Medium
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C$10 $
c If no current flows through the ammeter $(1),$ potential on the $20 \mathrm{\,W}$ resistance becomes $2 \mathrm{\,V}.$
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