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

Options

A. both the length and the radius of the wire are halved.
B. both the length and the radius of the wire are doubled.
C. the radius of the wire is doubled.
D. the length of the wire is doubled .

Answer

B

Explanation

(b) KEY CONCEPT : The heat produced is given by
`H = V^2/R and R=(rhol)/(pir^2) :. H= V^2 ((pir^2)/(rhol))`
or `H = (piV^2)/rho (r^2/l)`
Thus heat (H) is doubled if both length (l) and radius (r ) are doubled.