A certain wire has a resistance $R$. The resistance of another wire identical with the first except having twice its diameter is
A$2\,R$
B$0.25\,R$
C$4\,R$
D$0.5\,R$
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B$0.25\,R$
b $R \propto \frac{1}{A} \Rightarrow R \propto \frac{1}{{{r^2}}} \propto \frac{1}{{{d^2}}}$
[$d$ $=$ diameter of wire]
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