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ICSE Guess > ICSE Papers > Important Questions > Class X > 2008 > Physics > Physics By :- M. P. Keshari

Q. 1. Does the boiling point of water changes with altitude ? If so, how ?

Q. 2. Define specific latent heat of vaporisation.

Q. 3. Which material is the calorimeter commonly made of ?

Q. 4. 1 kg of ice at 0ºC is being continuously heated through an electric heater of 1kW. Assuming that all the heat is transmitted to ice, calculate the time interval in second for :

1. ice to completely melt to water at 0ºC,
2. water to get heated from 0ºC to 100ºC,
3. water at 100ºC to convert into steam.

[Given : Specific latent heat of ice= 3,36,000 J kg-1K-1

Specific heat capacity of water = 4,2200 J kg-1 K-1

Specific latent heat of steam = 22,60,000 J kg-1 K-1]

Ans. (i) 336 s (ii) 420 s (iii) 2,260 s

Q. 5. A given liquid changes into the gaseous state at a fixed temperature as well as at all temperatures.

(i) Name the process that takes place in each of the above two cases.

(ii) Mention two points of difference between the two cases in (i) above.

Q. 6. Define the term specific heat capacity of a substance. Give its SI unit.

A 30 g ice cube at 0ºC is dropped into 200 g of water at 30ºC. Calculate the final

temperature of water when all the ice cube has melted.

Given : Latent heat of ice = 80 cal g-1; Specific heat capacity of water = 1 cal g-1ºC-1

Ans. 15.65ºC

Q. 7. Explain how the following factors affect the rate of evaporation of a liquid :

1. Temperature of the liquid
2. Area of the exposed surface
3. Moisture in the surrounding air.

Q. 8. Define specific latent heat of fusion of ice. Give its SI unit.

Q. 9. What is the effect of increase in pressure on the melting point of ice and boiling point of water ?

Q.10. A piece of metal at 10ºC has a mass of 50 g. When it is immersed in a current of steam at 100ºC, 0.7 g of steam is condensed on it. Calculate the specific heat of metal.

[Given : Latent heat of steam = 540 cal/g] [Ans. 0.084 cal g-1 ºC-1 ]

Q. 11. Explain briefly:

1. Why hot bottles are very efficient for fomentation ?
2. How human body temperature is maintained at normal value(37ºC) when the atmospheric temperature rises as high as 45ºC ?

Q. 12. State two ways, other than direct heating, by which a given quantity of liquid can be made to evaporate more quickly.

Q. 13. The temperature recorded by a thermometer decreases when its bulb is covered with a piece of cloth soaked in sprit. Explain why.

Q. 14. 2 kg of ice melts when a jet of steam at 100ºC is passed through a hole drilled in a block of ice. What mass of steam was used ?

[Given : Specific heat capacity of water = 4,200 J/ kg ºC.
Specific latent heat of fusion of ice = 336 × 103 J/kg.
Specific latent heat of vaporisation = 2,268 × 103 J/kg. ]

Ans. 0.25 kg

Q.15. Why does evaporation always produce cooling ?

Q. 16. Explain why the surroundings become pleasantly warm when water in the lake starts freezing in cold countries.

Q. 17. If, in a central heating system, steam enters a radiator pipe at 100ºC and water leaves the radiator pipe at 100ºC, can this radiator pipe heat a room ? Give an explanation for your answer.

Q. 18. The graph represents a cooling curve for a substance being cooled from higher temperature to a lower temperature.

1. What is the boiling point of the substance ?
2. What happened to the region DE ?
3. Why is region DE shorter than the region BC ?

Q. 19. At what approximate temperature will water boil in a pressure cooker?

Q. 20. Explain why bottled soft drink are more effectively cooled by cubes of ice than by ice water.

Q. 21. 10 g of ice of 0 ºC absorbed 5,460 J of heat to melt and change into water at 50 ºC. Calculate the specific latent heat of fusion of ice. Given specific heat capacity of water is 4,200 J kg-1ºC-1.

Ans. 3,36,000 J

Q. 22. In an experiment to determine the specific latent heat of vaporisation of steam L, the following measurements were taken :

Mass of calorimeter + stirrer = x kg
Mass of water = y kg
Initial temperature of water = t1ºC
Final temperature of mixture = t2ºC

Given : S.H.C. of calorimeter and water are S1 and S2 respectively. Express L in terms of above data. Mass of condensity (steam condensed) = M kg.

Q. 23. It takes a much longer time to boil off (change to steam) a certain quantity of water, rather than to bring it to its boiling point from room temperature, say 25ºC. Explain the reason for this.

Q. 24. A hot solid of mass 60 g at 100ºC is placed in 100 g of water at 18ºC. The final steady temperature recorded is 20ºC. Find the specific heat capacity of the solid.

Ans. 0.04 cal/g ºC

Q. 25. (s. 0.04 cal/g ºC (i) Draw a labelled diagram of the apparatus you would use to determine the specific latent heat of vaporisation of steam by the method of mixture.

(ii) State two precautions, you would take, while performing the experiment with the apparatus.

Q. 26. (i) Calculate the mass of steam at 100ºCthat must be passed into 8.4 kg of water at 30ºC to raise the temperature of water to 80ºC. [Ans. 750 g]

(ii) Why do the surrounding become pleasantly warm when freezing starts in cold countries ?

Q. 27. In a laboratory experiment to measure specific heat capacity of copper, 0.02 kg of water at 70ºC was poured into a copper calorimeter with a stirrer of mass 0.16 kg initially at 15ºC. After stirring, the final temperature reached to 45ºC. Specific heat of water is taken as 4200 J/kg ºC.

1. What is the quantity of heat released per kg. of water per 1 ºC fall in temperature ?
2. Calculate the heat energy released by water in the experiment in cooling from 70 ºC to 45 ºC.
3. Assuming that the heat released by water is entirely used to raise the temperature of calorimeter from 15 ºC to 45 ºC, calculate the specific heat capacity of copper.

Ans. (i) 42000 J kg-1 ºC-1, (ii) 2100 J, (iii) 437.5 J/kg ºC]

Q. 28. A vessel of negligible heat capacity contains 40 g of ice in it at 0 ºC. 8 g of steam at 100 ºCis passed into the ice to melt it. Find the final temperature of contents of the vessel.

[Specific latent heat of vaporisation of steam = 2268 J/g,
Specific latent heat of fusion of ice = 336 J/g,
Specific heat capacity of water = 4.2 J/g]

Ans. 40 ºC

Q. 29. Explain why one feels ice cream at 0 ºCcolder than water at 0ºC.

Q. 30. (i) Define specific heat capacity of a substance. State its SI unit.

(ii)Give one example each where high specific heat capacity of water is used :

1. in cooling
2. as a reservoir.

Q. 31. (i) Does land cool at a slower or faster rate than water ? Give one reason for your answer.

(ii) Explain why steam pipes warm a building more effectively than hot water pipes in cold countries.

Q . 32. In a laboratory experiment for finding specific latent heat of ice, 100 g of water at 30 ºC was taken in calorimeter made of copper and of mass 10 g. When 10 g of ice at 0 ºCwas added to the mixture and kept within the liquid till the ice melted completely, the final temperature of the mixture was found to be 20 ºC.

1. What is the total quantity of water in the calorimeter at 20 ºC ?
2. Specific heat capacity of water and copper being 4.2 J/g ºC and 0.4 J/g ºC respectively, what quantity of heat would each release in cooling down to 20 ºCfrom the initial stage ?
3. Write an expression for the heat gained by ice on melting.
4. Calculate the value of the latent heat of fusion of ice from the data discussed above.

Ans. (i) 110 g, (ii) 40 J, (iii) {10 L + 840}J, (iv) 340 × 103 J/kg

Q. 33. (i) In winter, the weather forecast for a certain day was ‘severe frost’. A wise farmer watered his fields the night before to prevent frost damage to his crops. Why did he water his fields ?

(ii) 10125 J of heat energy boils off 4.5 g of water at 100 ºC to steam at 100 ºC. Find the specific latent heat of steam. [Ans. 2250 J/g]

Q. 34. (a) A thermos flask of negligible heat capacity contains 100 g of ice and 30 g of water.

(i) Calculate :

(1) the mass of steam at 100 ºCneeded to condense in the flask so as to just melt the ice
(2) the amount of water in the flask after condensation.
[Specific latent heat of vaporisation of steam = 2260 J/g.
Specific latent heat of fusion of ice = 336 J/g.
Specific heat capacity of water = 4.2 J/g ºC]

Ans. (a) 12.537 g (b) 142.537g

(ii) Is it possible to condense the water formed, back to ice by adding ice at 0 ºC ? Explain, giving a suitable reason to justify your answer.
(b) (i) State the Principle of Calorimetry.
(ii) Express 1 kW h in terms of S.I. unit of energy. [Ans. 3.6 × 105 J]
(iii) Which of the two, 1 g of ice at 0 ºC or 1 g of water at 0ºC contains more heat ? Give a reason for your answer.

Q. 35. Why does the temperature of the surroundings start falling when the ice of a frozen lake starts melting ?

Q. 36. Calculate the heat energy that will be released when 5 kg of steam at 100 ºC condenses to form water at 100 ºC . Express your answer in S.I. unit. (Specific latent heat of vaporisation of steam is 2268 kJ/kg). [Ans. 11340 kJ]

Q. 37. Water falls from the height of 50 m. Calculate the rise in temperature of water when it strikes the bottom. [g = 10 ms-2, specific heat capacity of water = 4200 Jkg-1ºC-1]

Ans. 0.12 ºC

Q. 38. A piece of ice is heated at a constant rate. The variation of temperature with the heat input is shown in the graph below :

1. What are represented by AB and CD ?
2. What conclusion can you draw regarding the nature of ice from the graph ?

fig

Q. 39. If there is no heat loss to the surroundings, the heat released by the condensation of m1 g of steam at 100 ºC into water at 100 ºC can be used to convert m2 g of ice at 0 ºC into water at 0 ºC.

(i) Find :

[1] the heat lost by steam in terms of m1.
[2] the heat gained by ice in terms of m2.

(ii) Form a heat equation and find the ratio of m2 : m1 from it.

[Specific latent heat of vaporisation of steam = 2268 kJ/kg,
Specific latent heat of fusion of ice = 336 kJ/kg,
Specific heat capacity of water = 4200 J/kg ºC.]

Ans. (i){1} 2688m1 J, {2} 336m2 J. (ii) m2 : m1 = 8 : 1

Q. 40. Give two reasons as to why copper is preferred over other metals for making calorimeter.

Q. 41. Calculate the amount of heat released when 5 g of water at 20 ºC is changed into ice at 0 ºC. Specific heat capacity of water = 4.2 J/g ºC, specific latent heat of fusion of ice = 336 J/g. [Ans. 2100 J]

Q. 42. A piece of iron of mass 2 kg has a thermal capacity of 966 J/ ºC.

1. How much heat is needed to warm it by 15 ºC ?
2. What is its specific heat capacity in S.I. units.

Ans. (i) 14490 J, (ii) 483 J/kg ºC

Q. 43. (i) Define specific latent heat of vaporisation of a substance.

(ii) What is the principle of Calorimetry ?

Q. 44. Explain why water is used in hot water bottles for fomentation and also as a universal coolant.

Q. 45.Some hot water was added to three times its mass of cold water at 10 ºC and the resulting temperature was found to be 20 ºC. What was the temperature of the hot water ?

Ans. 50 ºC

Q. 46. Why are burns caused by steam more severe than those caused by boiling water at the same temperature ?

Q. 47. (i) What is meant by specific heat capacity of a substance ?

(ii) Why does the heat supplied to a substance during its change of state not cause any rise in its temperature ?

Q. 48. A substance is in the form of a solid at 0 ºC. The amount of heat added to this substance and the temperature of the substance are plotted on the following graph :

Fig

If the specific heat capacity of the solid substance is 500 J/kgºC, find from the graph :

1. The mass of the substance;
2. the specific latent heat of fusion of the substance in the liquid state.

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