Thermal properties

Question 1

3. What are the basic requirements of a cooking utensil in respect of specific heat, thermal conductivity and coefficient of expansion?

Answer 1

A cooking utensil should be of suitable material, which possesses small value of specific heat (C), large value of thermal conductivity (K) and low coefficient of expansion (a).

Question 2

4. How the fishes can survive in the extreme winter, when ponds and lakes are frozen?

Answer 2

Solution Fishes survive in pond even when the atmospheric temperature is below 0°C. It is because of anomalous expansion of water. When the temperature falls below 0°C water changes into ice and rises to the top and ice being poor conductor of heat helps to keep water below it at 4°C and fish can live in pond water.

Question 3

8. Explain why a beaker filled with water at 4 0C overflows if the temperature is decreased or increased?

Answer 3

Water density is maximum at 4oC, so whether it is cooled to temperature below 4oC or warmed to temperature above 4oC, in both the cases its density will decrease. In other words it will expand and overflow in both the cases.

Question 4

10. Why is a small gap left between the iron rails of railway tracks?

Answer 4

Keeping the gap at the joint of two rail tracks, helps in expansion of the tracks during high temperature. If there is no gap between them, the expansion of the tracks lead to bending of the tracks and in turn can cause accidents.

Question 5

11. Pendulum clocks generally run fast in winter and slow in summer. Why?

Answer 5

Pendulum clocks become slow in summer because the length of the pendulum increases due to which the time period increases and the pendulum takes more time to complete one oscillation. Thus it becomes slow in summer. In summer due to an increase in the temperature of the atmosphere, the length of the pendulum (l) will increase.

Question 6

12. Why is water preferred to any other liquid in hot water bottles?

Answer 6

Water is preferred to any other liquid in the hot water bottles because the specific heat of water is high. It does not cool fast. Also water contains more amount of heat for a given mass and for a given rise in temperature as compared to other liquids. due to it, the hot water bottlws provides more warmth for longer time.

Question 7

13. The coolant used in nuclear reactor should have high specific heat. Why?

Answer 7

The function of a coolant in a chemical or nuclear plant is to absorb as much heat as possible and prevent rise in temperature of the system. The coolant should have a high specific heat. This is because higher the specific heat of the coolant, higher is its heat-absorbing capacity and vice versa.

Question 8

14. Birds swell their feathers in winter. Why?

Answer 8

By doing so, they enclose more air between feathers and their body. the air being bad conductor of heat slows down the flow of our body heat to the outside. thus, a bird feels warmer in winter by swelling their feather.

Question 9

15. Explain why a brass tumbler feels much colder than a wooden tray on a chilly day?

Answer 9

Brass is a good conductor of heat. When one touches a brass tumbler, heat is conducted from the body to the brass tumbler easily. Hence, the temperature of the body reduces to a lower value and one feels cooler.

Wood is a poor conductor of heat. When one touches a wooden tray, very little heat is conducted from the body to the wooden tray. Hence, there is only a negligible drop in the temperature of the body and one does not feel cool.

Thus, a brass tumbler feels colder than a wooden tray on a chilly day.