Frank Solutions for Chapter 5.1 Calorimetry Class 10 Physics ICSE

Exercises


1. What do you mean by thermal energy?
Answer 
Thermal energy is energy that is powered by a heat source. For e.g.: an electric heater generates thermal energy that can be used to warm a cold room in the winter.

2. Is heat a form of energy?
Answer 
Yes, heat is a form of energy.

3. What do you understand by the term 'temperature'?
Answer 
Temperature is a physical property that quantitatively expresses the common notions of hot and cold. It is the degree of hotness or coldness of a body or environment.

4. Distinguish between heat and temperature.
Answer

Heat

Temperature

1. It S a form of energy in motion.

2. It is the cause of temperature. It is the heat that causes a change in the temperature of a body.

3. It does not determine the direction of flow of heat.

4. It s measured in joule or calorie.

1. It is the degree of hotness or coldness of a body. 2. It is the effect of heat.

3. It determines the direction of flow of heat. It always flows from a body at a higher temperature to a body at a lower temperature.

4. It is measured on the Celsius (CC), Fahrenheit (°F) or the Kelvin (K) scale

5. What is the SI unit of heat and temperature?
Answer 
The SI unit of heat energy is joule (J).

6. Define 1 joule.
Answer 
1 joule is the amount of heat required to raise the temperature of 1 kg of a substance, that has specific heat capacity 1J/kgK, through 1oC.

7. Which is bigger: 1 joule or 1 calorie?
Answer
1 J = 4.2 cal. So, 1 joule is bigger than 1 calorie.

8. Name the instrument used to measure temperature.
Answer 
A thermometer is used to measure temperature.

9. (i) Plot a graph taking oC on the Y-axis and the corresponding oF along the X-axis.
(ii) Plot a graph taking oF along the Y-axis and the corresponding oC on the X-axis.
Answer 

10. Name the physical quantity that measures the degree of hotness.
Answer 
Temperature is the physical quantity that measures the degree of hotness.

11. A substance is heated gradually. Does its energy increase or decrease?
Answer
Its energy increases on heating.

12. Why do the molecules of a gas move about freely?
Answer
Gas molecules have very weak or no bonds at all and the spaces between gas molecules are very large. So, the molecules of a gas move about freely.

13. Name the two scales used for measuring temperature.
Answer
Two scales for measuring temperature are
  1. Celsius scale
  2. Fahrenheit scale

14. What kind of thermometer is commonly used?
Answer 
'Liquid-in-glass' kind of thermometer is commonly used.

15. What is the other name of Doctor's thermometer?
Answer
Doctor's thermometer is also called Clinical thermometer.

16. Express the melting point of ice on the Celsius scale and the Fahrenheit scale.
Answer 
Melting point of ice :
On Celsius scale : 0°C
On Fahrenheit scale : 

17. Which scale of temperature is commonly used and why?
Answer 
Celsius scale and Fahrenheit scale are two commonly used scales of temperature because the former is based on the freezing point of water as 0oC and boiling point of water as 100oC. The same points on the Fahrenheit scale are 32oF and 212oF.

18. What is the normal body temperature of a healthy person on the Celsius scale?
Answer 
The normal body temperature of a healthy person is 37oC.

19. Write down a relationship to convert temperature on the Fahrenheit to Celsius scale.
Answer 

20. What are the upper and lower fixed points on the Fahrenheit scale?
Answer
Lower fixed point = 32°F
Upper fixed point = 212°F

21. Describe the Celsius scale of temperature.
Answer 
In Celsius scale, melting point of ice and boiling point of water are referred as "lower fixed point" and "upper fixed point" respectively. The temperature difference between the reference points is divided into 100 divisions and each division is called "one degree Celsius" (1°C). Thus, the melting point of ice is taken as 0°C and the boiling point as 100°C.

22. Which represents a greater temperature rise, 200C or 200 F?
Answer 

23. Express -40°C on the Fahrenheit scale.

Answer 


24. Express 212°F on the Celsius scale.
Answer 

25. Express the temperature of 0 K on the:
(a) Celsius scale
(b) Fahrenheit scale
Answer 

26. What is absolute zero?
Answer 
Absolute zero is the temperature at which volume or pressure of an ideal gas becomes nil. It is 0 degrees on the Kelvin scale, which translates to -273°C (or -459.4°F).

27. If the temperature of a body is 20°C, what will be the corresponding temperature on the Kelvin scale?
Answer 
K = (C + 273)
= (20 + 273 
= 293 K 
⇒ 20°C ≡ 293 K 
The corresponding temperature of the body on the Kelvin scale is 293 K. 

28. Convert 37°C temperature to the Fahrenheit scale.
Answer 

29. Write the SI unit of:
(i) Amount of heat
(ii) Heat capacity
(iii) Specific Heat capacity
Answer 

SI unit of:

  1. Amount of heat - joule
  2. Heat Capacity - joule per Kelvin
  3. Specific Heat Capacity - joule per kilogram per Kelvin


30. A bucket contains 8 kg of water at 250 C. 2 kg of water at 800 C is poured into it. Neglecting the heat energy absorbed by the bucket, calculate the final temperature of water.
Answer
Let C be the specific heat capacity of water.
Let final temperature of the mixture be 8°C.
Heat energy lost by hot water = Heat energy gained by cold water
2× C × (80-θ) = 8 × C × (θ-25)
or, 2(80-θ) = 8(θ-25)
or, 80-θ = 4θ-100
or, 5θ = 180
θ = 36
So, the final temperature of water will be 36°C. 

31. What mass of a liquid A of specific heat capacity 0.84 J K-1 and at a temperature 40°C must be mixed with 100 g of a liquid B of specific heat capacity 2.1 J g-1 K-1 and at 20°C, so that final temperature of mixture becomes 32°C?
Answer
Let m be the mass of liquid A. 
Assuming that there is no heat loss, 
Heat energy given by A = Heat energy taken by B 
or, m × 0.84 ×(40 - 32) = 100 ×2.1 × (32 - 20)

32. Write the approximate value of specific heat capacity of water in SI unit.
Answer
Specific heat capacity of water is 4200 Jkg-1K-1.

33. The sp. Heat capacity of water is 4200 J kg-1 K-1. What information does this convey?
Answer 
This means that 4200 J of heat is required to raise the temperature of 1kg of water by 1K.

34. Give one example each where high specific heat capacity of water is used
(i) In cooling,
(ii) As heat reservoir.
Answer 

(i) In cooling - Water is used in the cooling systems of automobiles and other engines.
(ii) As heat reservoir - In cold countries, water is used as a reservoir for wine and juice to avoid their freezing. The reason is that water can provide more heat to the bottles due to its high specific heat capacity. Hence, they do not cool down further to freeze.

35. What is a calorimeter? Why is it made of copper? Give two reasons.
Answer 
A calorimeter is a device used to measure the quantity of heat transferred to or from an object.
It is made of copper because:
  1. Copper is a good conductor of heat so it attains the temperature of its contents in a very short time.
  2. It has low specific heat (390 Jkg-1K-1). Therefore, it will take only a very little part of the heat energy given out in the experiment.

36. A piece of iron of mass 2.0 kg has a thermal capacity of 966 J/°C. Find: (i) Heat energy needed to warm it by 15°C, and (ii) Its specific heat capacity in SI unit.
Answer 

37. Why do the farmers fill their fields with water on a cold winter night?
Answer 
Farmers fill their fields with water on a cold winter night to protect the crops from frost. In the absence of water, if on a cold night the temperature of the surroundings fall below 0°C, then the veins of the plants shall freeze. Due to anomalous expansion of water, ice shall occupy more volume than water. As a result of this expansion, veins shall burst and crops shall be destroyed. But water sprinkled on the crops shall not allow the temperature of the veins to fall below 0°C.

38. The temperature of 600 g of cold water rises by 15°C when 300 g of hot water at 50°C is added to it. What was the initial temperature of the cold water?
Answer 
Let the initial temperature of cold water be t and the final temperature of the mixture be  θ.
Rise in temperature of cold water, (θ -t) = 15°C.
Heat gained by cold water = Heat given out by hot water 
or, 600 × C × 15 = 300 × C× (50 -θ)

39. Define the term 'heat capacity' and state its unit.
Answer 
Heat capacity of a body is the quantity of heat required to raise its temperature by 1oC. It depends upon the mass and the nature of the body.
Units: J/oC or calorie/oC

40. Define the term 'specific heat capacity' and state its unit.
Answer 
Specific heat capacity is the amount of heat required to raise the temperature of 1 kg of the substance by 1oC.
Units: j/kgK or calorie/g oC

41. 0.5 kg of lemon squash at 30°C is placed in a refrigerator which can remove heat at an average rate of 30 Js-1. How long will it take to cool the lemon squash to 5°C?(Sp. heat capacity of lemon squash = 4200 J kg-1°C-1.)
Answer 
Change in temperature of lemon squash = 30 -5 = 25°C 
Heat lost  by lemon squash, Q = m × C ×ΔT
Q = 0.5 × 4200× 25 = 52500
Rate at which heat is removed is 30 Js-1.

42. Describe a method to determine the specific heat capacity of a solid, like a piece of copper.
Answer 
The given solid is weighed and then heated by placing it in a beaker containing boiling water. The steady temperature of the solid is noted. A calorimeter with stirrer is weighed. The calorimeter is then filled with water and weighed again. Thus, the mass of water used is calculated. Initial temperature of water is noted. Solid is then transferred into calorimeter. The contents are stirred and final temperature is noted. Mass of calorimeter with stirrer = m1 g
Specific heat capacity of calorimeter = C1 (given)
Mass of water taken = m2 g
Specific heat capacity of water = C2 (given)
Mass of solid = mJ g
Specific heat capacity of the solid (to be determined) = CJ 
Initial temperature of the solid = x°C
Initial temperature of water + Calorimeter = y° C
Final temperature of the mixture = CC
Heat lost by the solid = Heat gained by the calorimeter and water 

43. Discus the role of high specific heat capacity of water with reference to climate in coastal areas.
Answer 
The specific heat capacity of water (4200 J Kg-1 K-1) is about five times as that of sand. Due to which water takes long time to get heated up and equally long time to get cooled. Thus, large temperature difference between the land and the sea causes formation of land and sea breezes.

44. State the principle of calorimetry.
Answer 
Principle of Calorimetry:
When a hot body is mixed or kept in contact with a cold body, there is a transfer of heat from hot body to cold body such that
Total heat gained by colder body = Total heat lost by the hot body,
if there is no loss of heat to the surroundings.

45. Water is used as an effective coolant. Give reason.
Answer 
Water is used as an effective coolant since it has a high value of specific heat capacity (4200 J kg-1K-1).
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