A constant voltage is applied between the two ends of a uniform metallic wire. Some heat is developed in it. The heat developed is doubled if

Answer: BSolution: (b) KEY CONCEPT : The heat produced is given by
$H=\frac{V^2}{R}\text{and}R=\frac{\rho l}{\pi r^2}\therefore H=V^2\left(\frac{\pi r^2}{\rho l}\right)$
or $H=\frac{\pi V^2}{\rho }\left(\frac{r^2}{l}\right)$
Thus heat (H) is doubled if both length (l) and radius (r ) are doubled.