A body cools in a surrounding which is at a constant temperature of ${\theta _0}$. Assume that it obeys Newton's law of cooling. Its temperature $\theta $ is plotted against time $t$ . Tangents are drawn to the curve at the points $P(\theta = {\theta _1})$ and $Q(\theta = {\theta _2})$. These tangents meet the time axis at angles of ${\varphi _2}$and ${\varphi _1}$, as shown

Hot water cools from ${60^o}C$ to ${50^o}C$ in the first $10$ minutes and to ${42^o}C$ in the next $10$ minutes. The temperature of the surrounding is ……… $^oC$

A body takes $5$ minute to cool from $80°C$ to $50°C$ .  …… $\min.$ it will take to cool from $60°C$ to $30°C$ , if room temperature is $20°C$ .

A container contains hot water at ${100^o}C$. If in time ${T_1}$ temperature falls to ${80^o}C$ and in time ${T_2}$ temperature falls to ${60^o}C$ from ${80^o}C$, then

For which method of convection Newton's law of cooling can be used ?