Group A
1. Define heat. What is its SI unit?
Answer: Heat is defined as the energy in flow from a body at higher temperature to another body at low temperature. Its SI unit is Joule (J).
2. State the factors on which the amount of heat present in a body depends.
Answer: The amount of heat present in a body depends upon its a) mass b) difference in temperature and c) specific heat capcity.
3. Define heat energy on the basis of molecular kinetic theory.
Answer: On the basis of molecular kinetic theory, heat energy is defined as the sum of kinetic energy of all molecules present in the body.
4. Define one calorie of heat energy.
Answer: One calorie of heat energy is defined as the amount of energy required to raise the temperature of 1 g mass of water through 1 degree Celsius.
5. Define one joule of heat energy.
Answer: One joule of heat energy is defined as the amount of energy required to raise the temperature of 1 kg mass of water through 1 degree Celsius.
6. Define temperature and write down its SI unit.
Answer: Temperature is defined as the measure of hotness or coldness of a body. Its SI unit is Kelvin (K).
7. Write down formula and SI unit of specific heat capacity.
Answer: The formula of specific heat capcity of a substance is$$\text{s = Q/(m’dt’)}$$Its SI unit is Joule/Kilogram-Kelvin.
8. Which principle is the construction of thermometer based on?
Answer: Constructuion of thermometer is based upon the principle that thermometric liquids expand or contract with the change in temperature.
9. Name any two liquids used in the thermometer.
Answer: Any two liquids used in the thermometer are a) Alcohol and b) Mercury.
10. Write down the boiling and melting points of mercury in normal pressure.
Answer: In normal pressure, the boiling point of mercury is 357oC and its melting point is -37.8oC.
11. What is clinical thermometer?
Answer: A type of thermometer used to measure human body temperature in hospital and clinics is called clinical thermometer.
12. Why is clinical thermometer used?
Answer: It is used to measure human body temperature.
13. What is digital thermometer?
Answer: A type of thermometer that gives the reading through a digital interface is called digital therometer.
14. What is maximum-minimum thermoeter?
Answer: A type of therometer designed to measure the maximum and miniumum temperature of a place is called maximum-minimum thermometer.
15. Name the instrument which is made on the basis of expansion of liquid on heating.
Answer: Thermometer is the instrument which is made on the basis of expansion of liquid on heating.
16. What is the body temperature of a healthy human?
Answer: The body temperature of a healthy human is 98.6oC.
17. Write two factors that affect heat energy.
Answer: Two factors affecting heat energy are a) mass of the body b) specific heat capcity of the body.
18. What is the boiling point of water in Kelvin unit?
Answer: The boiling point of water in Kelvin unit is 373 K.
19. Write down the formula of heat equation.
Answer: The formula of heat equation is $\text{Q = ms ‘dt’}$.
20. What is meant by 1 calorie heat?
Answer: 1 calorie heat energy is defined as the amount of energy required to raise the temperature of 1g mass of a water through unit degree celsius.
21. What is the value of specific heat capcity of water?
Answer: The value of specific heat capacity of water is 4200 J/kg-K.
22. What is the relation between the specific heat capacity and the rate of increase or decrease in its temperature?
Answer: Specific heat capacity of a body is inversely related with the rate of increase or decrease in its temperature.
Group B
1. What is the relation among the amount of heat energy contained by a body, its mass and kinetic energy of the molecules?
Answer: The amount of heat energy contained by a body is the sum of kinetic energy of all molecules present in that body. Kinetic energy depends upon its mass.
2. Write any two differences between heat and temperature.
Answer: Differences between heat and temperature are:
| Heat | Temperature |
|---|---|
| It is the sum of kinetic energy of all the molecules present in a body. | It is the average kinetic energy of all the molecules present in a body. |
| It is a cause. | It is an effect. |
| It is a derived physical quantity. | It is a fundamental physical quantity. |
3. What do you mean by the specfic heat capcity of a substance?
Answer: The amount of heat required to raise the temperature of a unit mass of a substance through unit temperature difference is meant by specific heat capcity of that substance.
4. What is the meaning of the statement that the specific heat capcity of water is 4200 J/kgoC?
Answer: It means that 4200 Joules of heat energy must be supplied to water of mass 1 kg to raise its temperature by 1 degree Celsius.
5. What is used to cool the engine of vehicles? Why?
Answer: Water is used to cool the engine of vehicles because of its high specific heat capcity. The same mass of water, as compared to other substances, can absorb a large amount of heat without getting much hotter.
6. What is used in hot water bags? Why?
Answer: Water is used in hot water bags because of its high specific heat capcity. It looses heat very slowly.
7. A new quilt is felt warmer than an old one. Why?
Answer: It is because a new quilt has more air spaces as compared to old one. Air is an insulator of heat and it traps heat. Thus, a new quilt is felt warmer than an old one.
8. A wet handkerchief is kept on the forehead of the patient suffering from fever. Why?
Answer: It is done to absorb the heat energy from the patient and decrease their temperature.
9. We wear woolen clothes during winter. Why?
Answer: It is because wool is an insulator of heat energy.
10. A solid melts on heating. Why?
Answer: On heating, the solid gains heat energy and according to kinetic theory of molecules, the average kinetic energy of molecules increases. This means its velocity increases therefore, molecules start vibrating. As a result, they move far apart as in liquid. And, a solid melts on heating.
11. Well water is felt warmer in winter. Why?
Answer: In winter, the temperature of the surrounding is lower than that of water. Therefore, when we touch well water, it feels warmer in winter.
12. Write any two differences between mercury and alcohol.
Answer: Any two differences between mercury and alcohol are:
| Mercury | Alcohol |
|---|---|
| It has uniform rate of expansion. | Its expansion is not uniform. |
| It is more toxic to human. | It is less toxic to human. |
13. Write any two differences between clinical thermometer and laboratory thermometer.
Answer:
14. If chilled coke and hot tea are kept together, tea cools down but coke gets warm, why?
Answer: Heat always flows from a body at higher temperature to a body at lower temperature. Hence, if chilled coke and hot tea are kept together, tea cools down but coke gets warm.
15. When hot iron nail is kept in cold water, the temperature of iron decreases while temperature of water increases, why?
Answer:
16. The temperature of mercury is more when equal amount of heat is given to one kilogram of water and mercury each, why?
Answer:
17. If equal amount of heat is given to the equal mass of water and alcohol substance, which warms up faster and why?
Answer:
18. Why do specific heat capacity of objects differ?
Answer:
19. During high fever, a wet clean cloth is kept on the forehead of the patient, why?
Answer:
20. The difference in temperature is low near sea. Give reason.
Answer: It is due to land breeze in night time and sea breeze in day time. This regulates the temperature and maintains it.
21. State the meaning of specific heat capcity of copper is 380 J/kgoC.
Answer: It means that 380 Joules of heat energy needs to be supplied to 1 kg mass of copper to raise its temperature through 1 degree Celsius.
22. Write down the cause that the night in desert is very cold and day of that place is very hot.
Answer: The major substance found in desert is sand which has very low specific heat capacity. During day, it gets heated up very fast while it gets cooled at night very fast. As a result, the night in desert is very cold and day of that place is very hot.
Group C
1. How is body temperature measured by using clinical thermometer? Explain.
Answer:
2. Write any three advantages of high specific heat capcity of water.
Answer:
3. Draw a neat and labeled figure showing maximum-minimum thermometer.
Answer:
4. Describe an activity to show that heat always flows from the body at high temperature to the body at low temperature.
Answer:
5. Write any three applications of high specific heat capacity of water.
Answer:
Group D
1. Study the given table and answer the following questions.
| Metal | Specific heat capacity |
| A | 140 J/kgoC |
| B | 460 J/kgoC |
| C | 380 J/kgoC |
i) The specific heat capcity of metal ‘A’ is 140 J/kgoC. What does it mean?
ii) If the same amount of heat energy is given to the same mass of all three metals at the same temperature, which one will gain the lowest temperature, why?
iii) Which metal will penetrate into the greatest depth if each with equal mass is put on wax slab after heating to 75oC each? Why?
Answer:
2. Specific heat capcities of three different substances are given below:
| Metal | Specific heat capacity |
| A | 910 J/kgoC |
| B | 380 J/kgoC |
| C | 470 J/kgoC |
i) What do you mean by specific heat capcity of A is 910 J/kgoC?
ii) Which above given substance will gain least temperature while heating equal mass of all the three substances supplied with equal amount of heat? Give reason.
iii) Which one will go down least in depth while keeping equal mass at the three substances heated for the same temperature of 100 oC and kept on a wax slab, why?
Answer:
3. Write any two advantages of high specific heat capcity of water. Calculate specific heat capcity of the alloy of pressure cooker of mass 1.5 kg is made, if quantity of heat necessary to raise its temperature by 60oC is 81 kJ.
Answer:
4. Why does frost bite occur in mountain climber? What will be the final temperature of a mixture of 10kg of water at 70oC and 20 kg of water at 10oC. Neglect the heat absorbed by the container.
Answer:
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