Does hot tea cool at a constant rate?

No, hot tea does not cool at a constant rate. According to Newton's law of cooling, the rate of cooling of an object is proportional to the difference in temperature between the object and its surroundings. As the temperature difference between the hot tea and the surrounding environment decreases, so does the rate of cooling. In the initial stage of cooling when the tea is very hot, it loses heat rapidly. As the temperature decreases the rate of cooling slows down.