Question

the resistance of 20 cm long wire is 5 ohms the wire is stretched to uniform wire of 40 cm length the resistance now will be( in ohm)-

Answer 1

Answer:

New resistance, R' = 20 ohms

Explanation:

Resistance of the wire is given by :

$R=\rho\dfrac{l}{A}$

Where

l and A is the length and the area of cross section of the wire.

When the wire is stretched (l' = 40 cm), its area changes while its volume remains the same.

So, $R=\rho\dfrac{l.l}{A.l}$

$R=\rho\dfrac{l^2}{V}$

$R\propto l^2$

So,

$\dfrac{R}{R'}=\dfrac{l^2}{l'^2}$

$\dfrac{5}{R'}=\dfrac{20^2}{40^2}$

So, R' = 20 ohms

Hence, this is the required solution.