NEET Physics: Physics - Thermal Properties questions with solutions

Q1. A hot liquid is kept in a big room. The logarithm of the numerical value of the temperature difference between the liquid and the room is plotted against time. The plot will be very nearly

1. a straight line
2. a circular arc
3. a parabola
4. an ellipse.

Answer: a straight line

By Newton’s law of cooling, the temperature difference decays exponentially with time. The logarithm of an exponential function is linear in time, so the plot is very nearly a straight line.

Q2. Water is poured into a pan and heated over a flame. After some time, the hot water begins rising to the top. Which type of heat transfer is involved in this?

1. conduction
2. convection
3. radiation
4. thermal expansion E. specific heat

Answer: convection

Convection is heat transfer by the movement of a fluid. In heated water, the warmer water becomes less dense and rises while cooler water sinks, creating circulating currents.