CONCEPTUAL PROBLEMS

1. Why do you think that the latent heat of vaporization is so much larger than the latent heat of fusion of substance?
2. How can water be boiled in a paper cup?
3. Why does steam at 100^oC cause severe burns than that water at 100^oC?
4. Groundnuts are fried along with sand, why?
5. Explain the significance of anomalous expansion of water with an example observed in nature.
6. Make difference between “specific heat” and “latent heat” of a body with definitions.
7. A medical officer prescribes to put wet clothes on the forehead of a person suffering from high fever, why?
8. Why does the temperature of ice fall when some salt is added to it?
9. If you add heat to an object, do you necessarily increase its temperature? Justify your answer.
10. Why do you feel cool in the mouth when you eat halls?
11. Why does food cook faster in a pressure cooker than in an open pot?
12. Explain why a person feels cooling when he pours a little sprit on his hand.
13. During a high fever, a wet cloth is kept on the forehead of a person. Why?
14. How is it that ice cream appears cooler to the mouth than ice at 0^oC?
15. If you wet your hand and pickup an ice tray that is below 0^oC, your hand may stick to it. This does not happen to wood. Why?
16. Why do we feel cold when we spray perfume on our body?
17. During winter, the animals curl into a ball. Explain, why?
18. When you come out of swimming pool, you feel cold. Why?
19. Why is a spark produced when two stones are stricken against each other?

NUMERICAL PROBLEMS

1. A copper calorimeter of mass 300 gm contains 500 gm of water at temperature 15^oC. A 560 gms block of aluminium of temperature 100^oC is dropped in the calorimeter and the temperature is observed to increase to 22.5^oC. Find the specific heat capacity of aluminium. (Specific heat capacity of copper (s_c) = 400 JKg^-1K^-1). Ans: 383.64 JKg^-1K^-1
2. A substance takes 3 minutes in cooling from 50°C to 45°C and takes 5 minutes in cooling 45°C to 40°C. What is the temperature of the surroundings? Ans: 35^oC
3. How much heat is required to convert 10 kg of ice at – 10° C into steam at 100° C? (Sp. heat of ice = 2100 Jkg^-1 K^-1, latent heat of fusion of ice = 3.36 x 10⁵ Jkg^-1, latent heat of vaporization = 2.268 x 10⁶ Jkg^-1). Ans: 3.02 x 10⁷J
4. A mixture of 500 g water and 100 g ice at 0^oC is kept in a copper calorimeter of mass 200 g. How much steam from the boiler be passed to the mixture so that the temperature of the mixture reaches 40^oC? (Latent heat of fusion of ice = 3.36 x 10⁵ JKg^-1, specific heat capacity of copper = 400 Jkg^{-1 o}C^-1, latent heat of vaporization of steam = 2.26 x 10⁶ Jkg^-1). Ans: 54.8 gm
5. What is the result of mixing 100 gm of ice at 0^oC into 100 gm of water at 20^oC in an iron vessel of mass 100 gm? Latent heat of fusion of ice = 80 calg^-1, specific heat capacity of iron = 0.1 calg^{-1 o}C^-1. Ans: 72.5 gm ice, 127.5 g of water, at 0^oC
6. In an experiment on the specific heat of a metal, a 200gm block of metal at 150^oC is dropped in a copper calorimeter of mass 270 gm containing 150 cm³ of water at 27^oC. The final temperature is 40^oC. Calculate the specific heat of the metal. (Given S_c = 390 JKg^{-1 o}C^-1, S_w = 4200 JKg^{-1 o}C^-1). Ans: 434.5 JKg^{-1 o}C^-1
7. A copper pot with mass 0.5 kg contains 0.170 kg of water at a temperature of 20^oC. A 0.250 kg block of iron at 85^oC is dropped into the pot. Find the final temperature assuming no heat loss to the surroundings. Specific heat capacity of copper = 390 JKg^-1K^-1, Specific heat capacity of iron = 470 Jkg^-1K^-1. Ans: 27.45^oC    
8. Find the result of mixing 0.8 kg of ice at – 10^oC with 0.8 kg of water at 80^oC. (S_w = 4200 Jkg^-1K^-1, S_i = 2100 Jkg^-1K^-1, L_f = 3.36 x 10⁵Jkg^-1). Ans: 0.05 kg ice, 1.55 kg of water at 0^oC
9. From what height should a block of ice be dropped in order that it may melt completely? (Latent heat of ice = 3.36 x 10⁵ J/Kg, g = 10 m/s²). Ans: 3.36 x 10⁴ m
10. How much heat is required to convert 5 kg of ice at – 10^oC into steam at 100^oC? (Sp. heat of ice = 2100 Jkg^-1 K^-1, latent heat of fusion of ice = 3.36 x 10⁵ Jkg^-1, latent heat of vaporization = 2.268 x 10⁶ Jkg^-1). Ans: 1.52 x 10⁷ J
11. A ball of copper weighing 400 gm is transferred from a furnace to a copper calorimeter of mass 300 gram and containing 1 kg of water at 20^oC. The temperature of water rises to 50^oC. What is the original temperature of the ball? Specific heat capacity of copper = 400 Jkg^{-1 o}C^-1. Ans: 860^oC
12. A copper calorimeter of mass 300 gram contains 500 grams of water at 15^oC. A 560 gram of aluminium ball at temperature of 100^oC is dropped in the calorimeter and the temperature is increased to 25^oC. Find the specific heat capacity of aluminium. Ans: 528.5 Jkg^{-1 o}C^-1
13. 10 gm of steam at 100^oC is passed into a mixture of 100 gm of water and 10 gm of ice at 0^oC. Find the resulting temperature of the mixture. Ans: 46.6^oC
14. What is the result of mixing 10 gm of ice at 0^oC into 15 gm of water at 20^oC in a vessel of mass 100 gm and specific heat 0.09? Ans: Amount of ice melt is 6 gm and final temperature of mixture is 0^oC
15. Calculate the difference in temperature between the water at the top and bottom of a waterfall 200 m high. (Specific heat of water = 4200 JKg^-1K^-1). Ans: 0.48 K
16. What is the result of mixing 100 g of ice at 0^oC and 100 g of water at 100^oC? Latent heat of fusion of ice = 336 x 10³ JK^-1, specific heat of water = 4200 Jkg^-1K^-1. Ans: 10^oC
17. How much heat is needed to change 10 g of ice at -10^oC to steam at 100^oC? (Specific heat capacity of ice = 0.5 calg^{-1 o}C^-1, latent heat of fusion of ice = 80 calg^-1, latent heat of vaporization = 540 calg^-1). Ans: 30450 J
18. From what height a block of ice be dropped in order that it may completely melt. It is assumed that 20% of energy of fall is retained by ice. (L = 80 calg^-1). Ans: 168000 m
19. 50 g of ice at – 6^oC is dropped into water at 0^oC. How many grams of water freeze? (SP heat capacity of ice = 2000 JKg^{-1 o}C^-1). Ans: Mass of water frozen = 1.786 x 10^-3 kg
20. Evaporation of perspiration is an important mechanism for temperature control of warm – blooded animals. What mass of water must evaporate from the surface of an 80 kg human body to cool it by 1^oC? The specific heat capacity of the human body is approximately 0.1 calg^-1oC^-1 and the latent heat of vaporization of water at the body temperature is 577 calg^-1.Ans: 0.0139 kg