Question

A beaker full of hot water is kept in a room. If it cools from ${80}^{o}C$ to ${75}^{o}C$ in $t_1$ minutes, from ${75}^{o}C$ to ${70}^{o}C$ in $t_2$ minutes and from ${70}^{o}C$ to ${65}^{o}C$ in $t_3$ minutes, then

• A. $t_1<t_2<t_3$
• B. $t_1>t_2>t_3$
• C. $t_1=t_2=t_3$
• D. $t_1<t_2=t_3$

Answer 1

The correct option is A $t_1<t_2<t_3$

Newton's $cooling$ law tells that more the temperature difference with surrounding less will be time taken to cool or more will be cooling rate.

As the temperature of the beaker is decreasing so the temperature difference with the surrounding is also decreasing.

So

$t_1$ should be minimum and $t_3$ should be highest so option A is correct.