HEAT
I. ANSWER THE FOLLOWING QUESTIONS 5 X 1 = 5 M
1. Define i) Dew ii) Humidity?
A. Dew: 1. During winter nights, the atmospheric temperature goes down.
2. The air becomes saturated with vapour and the water droplets condensed on the surfaces of window panes, flowers, grass etc are known as dew.
Humidity: The amount of water vapour present in air.
2. Define latent heat of vaporization?
A. The heat energy required to change 1gm of liquid to gas at constant temperature is called “latent heat of vapourization”.
3. What is principle of method of mixtures?
A. Net heat lost by hot body is equal to net heat gained by cold body.
4. Convert 353 K in to degree centigrade?
A. 353 - 273 = 80 ℃.
5. Define calorie?
A. The amount of heat required to raise the temperature of 1 gram of water by 1oC is called
‘Calorie’. 1 cal = 4.186 J
II. ANSWER THE FOLLOWING QUESTIONS 4 X 2 = 8 M
6. Why do we get dew on the surface of a cold softdrink bottle kept in open air?
A. 1. Air contains water molecules in the form of water vapour.
2. During their motion, the molecules of water in air, strike the surface of the cold soft drink bottle.
3. They lose their kinetic energy in the form of heat
4. They get converted into droplets and form dew on the surface of the bottle.
7. What would be the final temperature of a mixture of 50g of water at 20 ℃ temperature and 50g of water at 40 ℃ temperature?
A. m 1= 50g T1 = 20 ℃
m 2 = 50g T2 = 40 ℃
Final temperature, T= (m1T 1 + m2T 2 )/ (m1+ m2)
= 50 x 20 + 50 x 40 / 50 +50
= 1000+2000 / 100
= 3000 / 100
T = 30 ℃
8. Explain why dogs pant during hot summer days using the concept of evaporation?
A. 1. We have sweat glands in our skin.
2. During hot day, the temperature of the skin increases and water in the sweat glands starts evaporating.
3. This process of evaporation cools our body.
4. But dogs don’t have sweat glands on their skin.
5. The water molecules present on the tongue starts evaporate and helps to cool the interior parts
of the dogs body.
6. In this way dogs pant regulate their body temperature.
7. That’s why dogs pant during hot summer days.
9. Why do we sweat while doing work?
A. 1. Air contains water molecules in the form of water vapour.
2. During their motion, the molecules of water in air, strike the surface of the cold soft drink bottle.
3. They lose their kinetic energy in the form of heat
4. They get converted into droplets and form dew on the surface of the bottle.
III. ANSWER THE FOLLOWING QUESTIONS 3 X 4 = 12 M
10. How do you find the specific heat of a solid experimentally?
A. 1. Take a calorimeter and Measure the mass of it along with stirrer.
Mass of the calorimeter, m1 = ........................
2. Now fill one third of the volume of calorimeter with water. Measure its mass and temperature.
Mass of the calorimeter + water, m2 = .................
Mass of the water, m2 – m1 = ................
3. Temperature of water in calorimeter, T1= ...........
4. Take a few lead shots in a beaker with water. Heat them upto a temperature 100oC.
Let this temperature be T 2
5. Transfer the hot lead shots quickly into the calorimeter.
6. Now measure the temperature T 3 and mass of the calorimeter along with water and lead shots.
7. Mass of the calorimeter along with water and lead shots, m3 = .........
Mass of the lead shots, m3 – m2 = ............
8. Let the specific heats of the calorimeter, lead shots and water be SC,Sl
and Sw respectively.
9. According to the method of mixtures,
Heat lost by the solid = Heat gained by the calorimeter + Heat gained by the water
(m3- m2)Sl (T2- T3) = m1Sc (T3- T1)+( m2 – m1) Sw (T3- T1)
S1 = (m1Sc + (m2 - m1) Sw) (T3 - T1) / (m3 - m2) ( T2 - T3)
10. Knowing the specific heats of calorimeter and water, we can calculatethe specific heat of
the solid (lead shots).
11. Write the differences between evaporation and boiling?
A.
Evaporation Boiling
1. The process of escaping of molecules from the 1. The process in which the liquid phase
surface of a liquid at any temperature is called changes in to gaseous phase at a
evaporation. constant temperature is called boiling.
2. Evaporation takes place at any temperature. 2. Boiling takes place at constant temperature.
3. It is a cooling process. 3. It is a heating process.
4. It is a surface phenomenon 4. It is a bulk phenomenon
5. Temperature of the the system falls during 5. The temperature remains constant at
evaporation. during boiling.
12. Calculate required heat energy to change 12g of ice at -10 ℃ into water vapour at 100℃.
A.
Firstly we calculate for 1g of ice.
Stage-1 : Required heat energy to convert ice at -10℃ to ice at 0℃ = > Q1 = m.S.∆T
= 12x1/2x[0-(-10)]
[Spe.heat of ice = 1/2 cal/g℃] = 12x1/2x10
= 6 cal x 10 = 60 cal
Stage-2 : Required heat energy to convert ice at 0℃ to water at 0℃ = > Q2 = ML
= 12x80 = 960 cal
[ L= Latent heat of fusion of water 80 cal]
Stage-3 : Required heat energy to convert water at 0℃ to water at 100℃ = > Q3 = m.S.∆T
= 12x1x(100-0)
= 12x1x100 Cal
= 1200 Cal
Stage-4 : Required heat energy to convert water at 100℃ to water vapour
at 100℃ = > Q4 = ML
= 12x540
= 540 Cal x12
[ L= Latent heat of Vapourisation] = 6480 Cal
Required heat energy to change 12g of ice at -10℃
into water vapour at 100℃ = Q1+Q2+Q3+Q4
= 60+960+1200+6480
= 8700 Cal
Tags: Heat, Test, Sliptest, Evaporation, Principle of method of mixtures,Dew,Humidity,Boiling.
Answers, Specific heat of a substance, latent heat of vapourization,
0 Comments
Please do not enter any spam link in the comment box