Three rods of Copper, Brass and Steel are welded together to from a Y shaped structure. Area of cross-section of each rod `=4cm^2`. End of copper rod is maintained at `100^@C` where as ends of brass and steel are kept at `0^@C`. Lengths of the copper, brass and steel rods are `46, 13 and 12 `cm respectively. The rods are thermally insulated from surroundings excepts at ends. Thermal conductivities of copper, brass and steel are `0.92, 0.26 and 0.12` CGS units respectively. Rate of heat flow through copper rod is :

Options

A. `4.8"cal"//"s"`
B. `6.0cal/s`
C. `1.2cal/s`
D. `2.4cal/s`

Answer

A

Explanation

`(100-theta)/(R_(C)) = (theta-0)/(R_(B)) + (theta-0)/(R_(S))`
where `R = (l)KA` on solving we get `theta = 40` Heat flow per unit time through copper rod =`((100-40))/(l_(C))(K_(C)A_(C))= (60)/(46)xx 0.92 xx4 = 4.8"cal"//"s"`