Q. Two wires of same metal have the same length but their cross sections are in the retio 3:1. They are joined in series. The resistance of the thicker wire is $10\Omega$. The total resistance of the combination is
A) $5/2\ \Omega$
B) $40/3\ \Omega$
C) $40\ \Omega$
D) $100\ \Omega$
Explanation
(c) For the same length and same material,
$\frac{R_{2}}{R_{1}} = \frac{A_{1}}{A_{2}} = \frac{3}{1}or\ R_{2} = {3R}_{1}$
The resistance of thick wire, $R_{1} = 10\ \Omega$
The resistance of thin wire
$= 3R_{1} = 3 \times 10 = 30\ \Omega$
Total resistance $= 10 + 30 = 40\ \Omega$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.