An electric wire of length ‘$I$’ and area of cross-section $a$ has a resistance $R\, ohms$. Another wire of the same material having same length and area of cross-section $4a$ has a resistance of
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(b) $R = \frac{{\rho l}}{a}$ for first wire and $R$’=$\frac{{\rho l}}{{4a}} = \frac{R}{4}$for second wire.
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