Question

A uniform wire of length 8 metre has a resistance R. Now a portion of the wire of length x metre is elongated carefully so that the final length of the wire becomes 12 metre and total resistance of the wire becomes 4R. Then x is equal to

• A. 1 m
• B. 2 m
• C. 4 m
• D. 6 m

Answer 1

The correct option is A

1 m

$R^1=R_{AB}+R_{B{C}^1}4R=\frac{P(8-x)}{A}+\frac{P(x+4)}{\left(\frac{Ax}{x+A}\right)}$
Solving x = 1 m.