Question

A liquid is filled in a container which is kept in a room whose temperature is ${20}^{\circ }\text{C}$. When temperature of liquid is ${80}^{\circ }\text{C}$, it emits heat at the rate of $45{\text{cal s}}^{-1}$. When temperature of liquid falls of ${40}^{\circ }\text{C}$, using Newtons law of cooling, its rate of heat loss will be

• A. $15{\text{cal s}}^{-1}$
• B. $30{\text{cal s}}^{-1}$
• C. $45{\text{cal s}}^{-1}$
• D. $60{\text{cal s}}^{-1}$

Answer 1

The correct option is A $15{\text{cal s}}^{-1}$

According to Newton’s law of cooling,
Rate of heat loss $\propto$ Temperature difference
$\therefore \frac{R_2}{R_1}=\frac{40-20}{80-20}=\frac{1}{3}$
$R_2=\frac{R_1}{3}=\frac{45}{3}=15{\text{cal s}}^{-1}$