Question

Three identical conducting rods are connected as shown in figure. Given that ${\theta }_a={40}^{\circ }C,{\theta }_c={30}^{\circ }C$ and ${\theta }_d={20}^{\circ }C$. Choose the correct options

• A. Temperature of junction b is ${15}^{\circ }C$
• B. Temperature of junction b is ${30}^{\circ }C$
• C. Heat will flow from c to b
• D. Heat will flow from b to d

Answer 1

Answer: (B), (D)

Heat will flow from b to d



If heat flow from $b\to d$,
$\frac{40-T}{R}=\frac{T-20}{R}+\frac{T-30}{R}$
$\Rightarrow 40-T=2T-50$
$\Rightarrow 3T=90$
$\therefore T={30}^{\circ }C$

Why this question? Tip: We can assume the heat flow from any point and we will always get the correct answer. This fact can be utilized in situations where the direction of heat flow is not intuitive.