Q. 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
A) Both the length and radius of wire are halved
B) Both the length and radius of wire are doubled
C) The radius of wire is doubled
D) The length of wire is doubled
Explanation
(b) When length and radius both are doubled, in accordance with relation $R = \frac{\rho L}{A}$ the resistance of wire is reduced to 1/2 of its initial value. As at constant voltage the heat produced $H \propto 1/R$, hence heat produced is doubled
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.