Question

Three rods of copper, brass and steel are welded togeher to from a Y -shaped structure. Area of cross-section of each rod `=4 cm^(2)`. End of copper rod is maintained at `100^(@)C` whereas the ends of brass and steel are at `0^(@)C` . Lengths of copper, brass and steel rods are 46, 13 and 12 cm respectively. The rods are thermally insulated from surroundings except 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
A. `4.8 cal//s`
B. `6.0 cal//s`
C. `1.2 cal//s`
D. `2.4 cal//s`

Answer 1

Correct Answer - A
`Q=Q_(1)+Q_(2)`
`(0.92xx4xx(100-T))/(46) = (0.26xx4(T - 0))/(13) + (0.12xx4xx(T-0))/(12)`

On solving, `T=40^(@)C`
`:. Q=(0.92xx4xx60)/(46)`
`=4.8 cal//s`