A Copper $(Cu)$ rod of length $25\, {cm}$ and cross- sectional area $3\, {mm}^{2}$ is joined with a similar Aluminium $(Al)$ rod as shown in figure. Find the resistance of the combination between the ends $A$ and $B$ (in ${m} \Omega$)
(Take Resistivity of Copper $=1.7 \times 10^{-8}\, \Omega \,{m}$, Resistivity of Aluminium $=2.6 \times 10^{-8}\, \Omega \,{m}$ )
JEE MAIN 2021, Diffcult
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$\frac{1}{R}=\frac{1}{R_{1}}+\frac{1}{R_{2}}$
$R=\frac{R_{1} R_{2}}{R_{1}+R_{2}}=\frac{\ell}{A} \cdot \frac{\rho_{1} \rho_{2}}{\rho_{1}+\rho_{2}}$
$R=\frac{25 \times 10^{-2}}{3 \times 10^{-6}} \times \frac{1.7 \times 2.6 \times 10^{-16}}{4.3 \times 10^{-8}}$
$R=0.858\, {m}\, \Omega$
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