The instantaneous temperature difference between a cooling body and its surroundings,which obeys Newton's law of cooling,is $\theta$. Which of the following graphs represents the variation of $\ln \theta$ with time $t$?

Hot water cools from $60\,^{\circ}C$ to $50\,^{\circ}C$ in the first $10\,minutes$ and to $42\,^{\circ}C$ in the next $10\,minutes$. The temperature of the surroundings is ......... $^{\circ}C$

$A$ body cools from $60^{\circ}C$ to $50^{\circ}C$ in $10$ minutes. If the room temperature is $25^{\circ}C$ and assuming Newton's law of cooling to hold good,the temperature of the body at the end of the next $10$ minutes will be ......... $^{\circ}C$.

An ordinary body cools from $4\theta$ to $3\theta$ in $t$ minutes. The temperature of the body after the next $t$ minutes is (Assume Newton's law of cooling and room temperature as $\theta$).

$A$ body takes $4\, \text{min}$ to cool from $61^{\circ} \text{C}$ to $59^{\circ} \text{C}$. If the temperature of the surroundings is $30^{\circ} \text{C}$,the time taken by the body to cool from $51^{\circ} \text{C}$ to $49^{\circ} \text{C}$ is $....\, \text{min}$.

What is Newton's law of cooling used to determine in a laboratory?