Question

Liquid is filled in a vessel which is kept in a room with temperature $20^{o}C$. When the temperature of the liquid is $80^{o}C$, then it loses heat at the rate of $60\mspace{6mu} cal/\sec$. What will be the rate of loss of heat when the temperature of the liquid is $40^{o}C$

• A. $180\mspace{6mu} cal/\sec$
• B. $40\mspace{6mu} cal/\sec$
• C. $30\mspace{6mu} cal/\sec$
• D. $20\mspace{6mu} cal/\sec$

Answer 1

Answer: (D)

$20\mspace{6mu} cal/\sec$

Answer 2

Rate of loss of heat $\left( \frac{\Delta Q}{t} \right) \propto$temperature difference ∆θ

$\frac{\left( \frac{\Delta Q}{t} \right)_{1}}{\left( \frac{\Delta Q}{t} \right)_{2}} = \frac{\Delta\theta_{2}}{\Delta\theta_{1}}$ ⇒ $\frac{60}{\left( \frac{\Delta Q}{t} \right)_{2}} = \frac{80 - 60}{40 - 20}$ ⇒ $\left( \frac{\Delta Q}{t} \right)_{2} = \frac{20cal}{\sec}$