Heat Class 10 Notes – AP class 10 physics notes – for Academic exams and also for competitive exams also – ap class 10 physics notes
1. What is the difference between heat and temperature? (AS1)
(OR) Write any two differences between heat and temperature? (AS1) (OR) How can we differentiate heat and temperature? (AS1)
(OR) Are heat and temperature same physical quantities? Explain? (AS1)
A.
| Heat | Temperature |
| 1. Heat is a form of energy which flows from
hot body to cold body. |
1. The degree of coldness or degree of hotness
is called temperature. |
| 2. SI unit of Heat is Joule (J). | 2. SI unit of Temperature is Kelvin (K). |
2. Convert 200C into Kelvin scale? (AS1) (TQ)
(OR)Ravi noted the temperature of a substance in an activity as 200C. Express it in Kelvin.
A. Temperature in Kelvin =273 + Temperature in Celsius degrees.
200C =273+20 =293 K
Heat Class 10 Notes – AP class 10 physics notes
3. Define dew and fog? (AS1)
(OR) Differentiate dew and fog? (OR) Explain dew and fog?
A. Dew: The water droplets condensed on surface like windows, flowers and grass are known as dew.
Fog: Thick mist is called as fog.
Heat Class 10 Notes – AP class 10 physics notes
4. A samosa appears to be cool outside but it is hot when we eat it. Why? (AS1) (OR) Write an application of the specific heat capacity in daily life?
(OR) Why the temperature of the inner and outer parts of a samosa is different? Explain?
A. A samosa appears to be cool outside but it is hot when we eat it because of the Curry inside the samosa contains ingredients with higher specific heats.
5. Why water is used as a moderator in a nuclear reactor? (AS1) (OR) Which is used as moderator in the nuclear reactor? Why? (OR) How can we use water in a nuclear reactor? Why?
A. Water has greater specific heat values. Hence water is used as a moderator in a nuclear reactor.
Heat Class 10 Notes – AP class 10 physics notes
6. On which factors the rate of evaporation depends? (AS1)
(OR) Write the factors that the rate of evaporation depends? (AS1)
A. The rate of evaporation depends on its surface area, temperature and amount of water vapour already present in the surrounding air and wind speed.
7. Why does ice floats on water? (AS1) (OR) Ice floats on water. Explain? (AS1)
(OR) Is ice floats or sinks in water? Explain? (AS1) (OR) Give the reason for the ice floats on water? (AS1)
A. Ice floats on water because the density of ice is less than the density of water.
Heat Class 10 Notes – AP class 10 physics notes
8. Why do we sweat while doing work?
(OR) We get sweat while doing work. Why?
(OR) Give the reason to get sweat while we are doing work? (AS1)
A. 1. When we do work the water in the sweat glands starts evaporating.
2. This evaporation cools the body.
Heat Class 10 Notes – AP class 10 physics notes
9. Why do we feel cool when apply nail polish on nails? (AS1)
(OR) Application of nail polish is a cooling process. Explain? (AS1)
A. 1. Nail polish contains alcohol/spirit which evaporates faster.
2. Evaporation is a cooling process. So we feel cool.
10. When we clean the floor of our house with a wet cloth the floor dries up after some time. What happens to the water on the floor? (AS2)
(OR) While drinking water, Sreekar spilled some water on the floor. After sometime, the water disappeared from the floor. What happened to the water? (AS-2) (TS-June 2015)
(OR) The water on the floor is escaped when we clean the floor with water. Why?
A. The water on the floor is escaped as water vapour due to evaporation and mixed with surrounding air.
Heat Class 10 Notes – AP class 10 physics notes
11. What is meant by humidity? (AS1) (AP-March, 2015) (OR) Some amount of water molecules is present in air. What is its name? (AS1) (OR) How can we call the water vapour present in the air?
A.Humidity: The amount of water vapour present in air is called ‘humidity’.
12. Give an example to explain that evaporation is a cooling process? (AS1) (TS-March, 2015) (OR) Why does water kept in a pot remains cool? (AS6)
(OR) Explain the reason that the water inside the pot gets cool? (AS6)
A. 1. Pot has small holes. Water inside the pot starts evaporation through the holes by gaining heat energy from the pot.
2. Due to this evaporation process water in a pot tends to be cool.
Heat Class 10 Notes – AP class 10 physics notes
13. What is Latent Heat of Fusion? Write their units? (AS1) (TS-March, 2015) (AP-June, 2016) (OR)What is the required heat energy to convert 1gm of solid completely into liquid at a constant temperature?
Latent Heat of Fusion:
A. 1. The heat energy required to convert 1gm of solid completely into liquid at a constant temperature is called Latent Heat of fusion.
2. Latent heat of fusion, L =
3. Latent heat of fusion is 80cal/gm.
Units: 1. SI unit is J/kg.
2. CGS unit of is cal/gm.
Heat Class 10 Notes – AP class 10 physics notes – 2 MARKS QUESTION & ANSWERS
1. Why do we get dew on the surface of a cold soft drink bottle kept in open air? (AS1) (OR) What is condensation? Give an example?
(OR) When we keep a cold soft drink bottle in open air, we get dew on its surface.
Give the reason.
A. 1.When a cold soft drink bottle is kept in open air the particles of water vapor present in the surrounding air strikes the surface of cool drink bottle and form as water droplets.
2. These water molecules slow down and stick to surface of the bottle as its surface is cold.
3. These water droplets appear as dew on the surface of the bottle. 4.This is a condensation process.
2. If you are chilly outside the shower stall, why do you feel warm after the bath if you stay in bathroom? (TQ) (AS6)
(OR) Why do we feel warm after the bath? Explain with the basis of the concept involving in this? (OR) We feel warm after the bath if we stay in bathroom. Explain?
A. 1.The number of water vapour molecules per unit volume in the bathroom is greater than the number of vapour molecules per unit volume outside the bathroom.
2. When we try to dry ourselves with a towel, the vapour molecules surrounding us Condense on our skin.
3. Condensation is a warming process, hence we feel warm.
Heat Class 10 Notes – AP class 10 physics notes
3. Write the differences between evaporation and boiling? (AS1) (TQ) (OR) How do you compare evaporation and boiling?
(OR) How do you differentiate evaporation and boiling?
A.
| Evaporation | Boiling |
| 1. The process of escaping of molecules from the surface of a liquid at any temperature is called evaporation. | 1. The process in which the liquid phase changes to gaseous phase at a 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. | 2. It is a heating process. |
| 4. Temperature of the system falls during
evaporation. |
4. Temperature of the system remains
constant during this process. |
4. Does the surrounding air become warm or cool when vapour phase of H2O condenses? Explain? (AS1) (TQ)
(OR) Explain how condensation takes place in a system? How does it effect the surroundings? (OR) When vapour phase of H2O condenses, what changes we observe in the surrounding air?
A. The surrounds air becomes warm when vapour phase of H2O condenses.
Explanation:
1. When vapour phase of H2O condenses, it loses energy.
2. The energy lost by vapour phase of H2O is gained by the surrounding air.
3. Then the surrounding temperature increases and the surrounding air become warm.
4. So, condensation of water vapour to water (liquid) heats the surroundings.
Heat Class 10 Notes – AP class 10 physics notes
5. What would be the final temperature of a mixture of 50gm of water at 200C temperature and 50gm of water at 400C temperature? (AS1) (TQ)
(OR)What is the equilibrium temperature of the mixture of the same quantity of water at 200C & 400C.
A. Solution: Given m1 = 50g T1= 20C
m2 = 50 g T2 = 40C Final temperature, T = ?
Formula: 30C The final temperature of a mixture is 30C.
6. Your friend is not able to differentiate between evaporation and boiling. What questions do you ask to make him know the differences between evaporation and boiling? (AS2) (TQ)
(OR) Frame some questions to explain the processes evaporation and boiling?
(OR) Write some questions to understand the differences between evaporation and boiling? (AS1)
A. 1. What is meant by evaporation?
2. What is meant by boiling?
3. At what temperature evaporation takes place?
4. At what temperature boiling point takes places?
5. Why evaporation takes place at any temperature?
6. Why boiling takes place at constant temperature?
7. Which one is the cooling process?
8. Which one is the warming process?
9. In which process energy of the system increases?
10. In which process the energy of the system decreases?
7. Write briefly about the formation of dew? (AS1)
(OR) Explain the process of formation of dew? (OR) How the dew forms?
Formation of Dew:
A. 1. During winter nights, the atmospheric temperature goes down.
2. The surfaces of window-panes, flower, grass etc, become still colder.
3. The air near them becomes saturated with vapour and condensation begins.
4. The water droplets condensed on such surfaces are known as dew.
8. What happenes to the water when wet clothes dry? (AS1) (AP June 2015, March 2016) (OR) Explain how wet clothes dry?
A. 1. The process of escaping molecules from the outer surface of the liquid at any temperature is called evaporation.
2. When wet clothes dried, the water in them is escaped as water vapour due to evaporation and mixes with the air.
Heat Class 10 Notes – AP class 10 physics notes
9. Write briefly about the formation of fog? (AS1)
(OR) Why water drops (dew) form on flowers and grass during morning hours in winter season? (AS1) (OR) When do the water droplets float in the air? Explain? (TS-March, 2016)
Formation of Fog:
A. 1. During winter nights, the atmospheric temperature goes down.
2. If the temperature falls further, the whole atmosphere in that region contains a large amount of vapour.
3. So the water molecules present in vapour condense on the dust particles in air and form small droplets of water.
4. These droplets keep floating in the air and form a thick mist which restricts visibility.
5. This thick mist is called fog.
10. What role does specific heat capacity play in a watermelon to keep it cool for long time after removing it from a fridge on a hot day? (AS1) (AP-June, 2016)
(OR) Why does a watermelon take longer time to get cool and to get hot? (OR) Write one application of the specific heat capacity of water in daily life?
A. 1. Watermelon contains large percentage of water.
2. Water has higher specific heat value.
3. Greater specific heat means to increase the temperature of 1gm of water by 10C.
4. It requires 1 calorie of heat to reach 10C.It takes place for a long time.
5. Hence watermelon cools for a long time after removing it from a fridge on a hot day.
Heat Class 10 Notes – AP class 10 physics notes – 4 MARKS QUESTION & ANSWERS
1. Suggest an experiment to prove that rate of evaporation of liquid depends on its surface area and vapour already present in surrounding air? (AS1)
(OR) What are the factors that influence the evaporation process? Explain with an experiment?
A. I. Rate of evaporation depends on surface area.
Aim : To prove that the rate of evaporation of liquid depends on its surface area.
Apparatus : Two dishes of different surface area and water.
Procedure : 1. Take a small quantity of water in two dishes separately.
2. Keep the dishes under the fan and switch on the fan.
3. After some time observe the quantity of water in both dishes.
4. It is proved that the dishes contain larger surface area of water is fastly evaporated.
II. Rate of evaporation depends on vapour already present in it.
Aim : To show the rate of evaporation depends on vapour already present in it.
Apparatus : Two China dishes, spirit.
Procedure : 1. Take a few drops of spirit in two dishes.
2. One of the dishes is placed in the AC room and another one is in normal room.
3. After some time we notice that the spirit in the normal room disappears quickly.
4. This means that the rate of evaporation depends upon the vapour already present in the surrounding area.
2. Place a Pyrex funnel with its mouth-down in a sauce pan with full of water, in such a way that the stem tube of the funnel is above the water or pointing upward into air. Rest the edge of the bottom portion of the funnel on a nail or on a coin so that water can get under it. Place the pan on a stove and heat it till it begins to boil. Where do the bubbles form first? Why? Can you explain how a Geyser works using above experience? (AS4) (TQ)
A. 1. The boiling point of the water increases with increasing the pressure.
2. So the bubbles first form at the top of the funnel.
Working of Geyser:
1. The Geyser works on the principle of electrical energy converted into heat energy.
2. When heat energy increases, the pressure inside of the geyser also increases.
3. So, the bubbles of water will come out from the top portion of the Geyser.
4. This is the laboratory demonstration of working of Geyser.
Heat Class 10 Notes – AP class 10 physics notes
3. A and B are two substances. Their temperature is given in different cases? (AS4)
| 1 | 2 | 3 | 4 | 5 | |
| Substance A | 30oC | 50oC | -273oC | 10oC | 30oC |
| Substance B | 30oC | 30oC | 0K | 20oC | 30oC |
By using the above information answer the following questions.
i. In which of the cases A and B are in thermal equilibrium? Why?
ii. In which of the cases heat will be transferred from A to B?
iii. In which of the cases heat will be transferred from B to A?
A. i. In first and third cases. Because the temperatures are the same.
ii. In second case heat would be transferred from A to B.
iii. In fourth and fifth cases heat would be transferred from B to A.
4. Does transfer of heat take place in all situations? If not explain with the basis of thermal equilibrium? (OR) What is meant by a thermal equilibrium? Explain with suitable example? (AS1 or AS3)
A. Thermal equilibrium:
1. When two bodies are in thermal equilibrium, they are at same temperature.
2. The state of a thermal equilibrium denotes a state of body where it neither receives nor gives out heat energy.
Procedure:
1. When two bodies are placed in thermal contact, heat energy will be transferred from the ‘ hotter’ body to the ‘ colder’ body.
2. This transfer of heat energy continues until both bodies attain the same degree of hotness (or) coldness.
3. At this stage, we say that the bodies have achieved ‘ thermal equilibrium’ .
4. Thus, the state of thermal equilibrium denotes a state of a body where it neither receives nor gives out heat energy.
Ex: 1. If you are not feeling either hot or cold in your surroundings, then your body is said to be in thermal equilibrium with the surrounding atmosphere.
2. The furniture in the room is in thermal equilibrium with air in the room.
Heat Class 10 Notes – AP class 10 physics notes
5. How do you prove that the average kinetic energy of the molecules is directly proportional to the absolute temperature? (OR) If you have materials like food colour, bowl, hot water and cold water, then how can you find the relation between temperature and kinetic energy? (AS1) (AS3)
A. Procedure:
1. Take two bowls one with hot water and second with cold water.
2. Gently sprinkle food colour on the surface of the water in both bowls.
3. Observe the motion of the small grains of food colour.
Observation: We observe that the jiggling of the grains of food colour in hot water is more when compared to the jiggling in cold water.
Explanation:
1. We know that bodies possess kinetic energy when they are in motion.
2. As the speed of motion of particles (grain of food colour) in the bowls
Of water is different, we can say that they have different kinetic energies.
3. Thus we say that the average kinetic energy of molecules or particles of a hotter body is greater than that of a colder body.
4. So we can say that the temperature of a body is an indicator of the average kinetic energy of molecules of that body.
Conclusion:- The average kinetic energy of the molecules is directly proportional to the absolute temperature.
Heat Class 10 Notes – AP class 10 physics notes
6. Answer the following questions by using the data given in the table. (AS4) (AP March 2018)
| Substance | Specific heat (Cal/gm-oC) |
| Lead | 0.031 |
| Aluminium | 0.21 |
| Copper | 0.195 |
| Water | 1.00 |
| Iron | 0.115 |
(a) Write the Si Unit of Specific heat?
(b) Based on specific heat values arrange the substances given in ascending order?
(c) If we supply same quantity of heat, which substance will heat faster?
(d) Calculate the amount of heat required to raise the temperature of 1 kg of iron through 10oC?
A. (a) J/Kg-K
(b) Lead, Iron, Copper, Aluminium, Water.
(c) Lead. Because Low specific heat value substances heat quickly.
(d) Given: Mass, m = 1 Kg = 1000 gm
Change in Temperature, T = 10C Specific heat of Iron, S = 0.15 cal/gm- oC
Heat Energy required, Q = ms T = 1000 × 0.115 × 10 = 1150 cal.
7. Explain with an activity about the process of melting? (AS1) (TS-March, 2015) (OR) Suggest an experiment to show that when ice is converted into water, its temperature does not change? (AS-3) (TS-June, 2015) (OR) List out the required materials for conducting an activity of process of melting. Explain it with suitable activity? (AS1)
A. Melting: This process of converting solid into a liquid is called “Melting”.
Required materials:- Beaker, ice cubes, thermometer, burner etc.
Procedure:
1. Take small ice cubes in a beaker. Insert the thermometer into ice cubes in the beaker.
2. Observe the reading of the thermometer.
3. Now start heating the beaker keeping it on a burner.
4. Observe changes in the thermometer reading every 1 minute till the ice completely melts and gets converted into water.
5. You will observe that the temperature of ice at the beginning is equal to or below 0oC.
6. If the temperature of ice is below 0oC, it goes on changing till it reaches 00C.
7. When ice starts melting, you will notice no change in temperature though you are supplying heat continuously.
Heat Class 10 Notes – AP class 10 physics notes
8. Explain why dogs pant during hot summer days using the concept of evaporation? (AS1) (TQ)
(OR) How the evaporation does useful to the animals which have no sweat glands? (AP March 2015) (OR) You know dogs do not have sweat glands. Then how do they cool their bodies?
A. 1. Dogs do not have sweat glands on their skin and they do not have swatting facility.
2. When dogs pant, the water molecules present on the tongue and in the mouth starts to evaporate.
3. Evaporation is the cooling phenomenon.
4. This helps to cool the interior parts of the dog’s body.
9. Explain the procedure of finding specific heat of solid experimentally? (AS3) (AP June 2015) (OR) How do you determine the specific heat of solid by principles of methods of mixtures?
(OR) Harika wants to place a lid of more specific heat on a cooking vessel. For that she wants to know the specific heat of aluminum and copper. What are the apparatus she required? How would she conduct this experiment?
A. Aim: To find the specific heat of given solid.
Apparatus: Calorimeter, thermometer, stirrer, water, steam heater, wooden box and lead shots.
Procedure:
1. Let the mass of the calorimeter along with stirrer is ‘ m1’ gm.
2. Onethird of the volume of the calorimeter is filled with water and its mass is ‘ m2’ gm.
3. The temperature of the calorimeter is noted (T10C ).
4. The heated Lead pieces of mass (m3 gm) and temperature (T20C) are quickly transferred in to calorimeter, with minimum loss of heat.
5. Contents in the calorimeter are stirred and then resultant temperature (T30C) is noted.
6. Let the specific heats of the calorimeter, led shots and water are Sc, Sl and Sw respectively.
7. According to the principles of methods of mixtures,
Heat lost by the solid = Heat gain by the calorimeter + Heat gain by the water. (m3 – m2) Sl (T2 – T3) = m1 Sc (T3- T1)+(m2 – m1) Sw (T3 – T1)
(m3 – m2) Sl (T2 – T3) = [ m1 Sc+ (m2 – m1) Sw ] (T3 – T1)
S = [ m1 Sc+ (m2 – m1) Sw ] (T3 – T1) / (m3 – m2) (T2 – T3)
By using the above formula we calculate the specific heat of the solids (lead shots) experimentally.
Heat Class 10 Notes – AP class 10 physics notes
10. Write the factors that effect the process of evaporation? Explain with suitable examples? (AS1)
(AP March 2017)
A. Process of evaporation is effected by surface area, wind speed, humidity and temperature.
Ex:- 1. The water kept in a china dish evaporates faster than in a cup because of more surface area.
2. Water in wet clothes are kept under fan evaporates faster than in normal conditions.
3. Water in wet clothes evaporates faster on a less humid day than on a more humid day.
4. Wet clothes dry faster in summer season due to high temperature.
Heat Class 10 Notes – AP class 10 physics notes
Class 10th Physics & Chemistry AP Board Solution
Improve Your Learning
Question 1.
What would be the final temperature of a mixture of 50g of water at 20°C temperature and 50g of water at 40°C temperature? (AS1)
Answer:
Let the final temperature of the mixture of 50g of water at 20°C temperature and 50g of water at 40°C be T.
For the first solution i.e mixture of 50g of water at 20°C temperature: –
Let the mass of water be m1 = 50g
Let the temperature of water be = T1 = 20°C
Similarly, For the second solution i.e mixture of 50g of water at 40°C temperature: –
Let the mass of water be m2 = 50g
Let the temperature of water be = T2 = 40°C
Let the specific heat capacity of water be S.
The amount of heat gained by the cooler water sample is: –
Q1 = m1S(T – T1)
The amount of heat lost by the hotter water sample is: –
Q2 = m2S(T2 – T)
According to the principle of method of mixtures we know that: –
The amount of heat lost by the hotter sample = The amount of heat gained by the cooler water sample
∴ Q1 = Q2
⇒ T = 
⇒ T = 
⇒ T = 30°C
Hence, the final temperature of a mixture of 50g of water at 20°C temperature and 50g of water at 40°C temperature would be 30°C
Question 2.
Explain why dogs pant during hot summer days using the concept of evaporation? (AS 1)
Answer:
Dogs have tongues with large surface area. The water molecules which are present on the surface of the tongue of a dog gets evaporated while panting. This evaporation cools the area. Hence, dogs pant during hot summer days as panting promotes cooling effect and relieves them from the heat.
Question 3.
Why do we get dew on the surface of a cold soft drink bottle kept in open air? (AS1)
Answer:
When a cold soft drink bottle kept in open air the surrounding air is at a higher temperature then that of the surface of the bottle hence the vapor molecules in the air during their motion collide with the surface of the cold drink bottle which is cool. In this process they lose a huge amount of energy and get converted into droplets. It is these droplets that we see as dew on the surface of a cold soft drink bottle kept in open air.
Question 4.
Write the differences between evaporation and boiling? (AS1)
Answer:
Question 5.
Does the surrounding air become warmer or cool when vapor phase of H2O Condenses? Explain.
Answer:
When the vapor phase of H2O Condenses it transfers its energy to the surface upon which it condenses hence their kinetic energy is reduced and the difference in the kinetic energy is transferred to the vessel upon which they condense. Now as the kinetic energy of the vapor reduces it leads to a reduction in their temperature along with that of the surroundings. Hence, the surrounding air becomes cooler when vapor phase of H2O condenses.
Question 6.
Answer these. (ASI)
How much energy is transferred when I gm of boiling water at 100oc condense to water at 100C?
Answer:
when 1 g of boiling water at 100oC condense to water at 100oC there is no change in temperature and the energy transferred is given by the latent heat of vaporization of water which is equal to 2260 Joule.
Question 7.Answer these. (ASI)
How much energy is transferred when I gm of boiling water at 100oC cools to water at 0oC?
Answer:
Given: – Mass, m = 1g
Initial temperature = 100oC
Final temperature = 0oC
Change in temperature, ∆T = 100 oC
The specific heat capacity of water is, S = 1cal/g°C
We know that Q = mS∆T
Hence, energy transferred when 1g of boiling water at 100oC cools to water at 0oC: –
⇒ Q = mS∆T
⇒ Q = 1 × 1 × 100
⇒ Q = 100cal
Question 8. Answer these. (ASI)
How much energy is released or absorbed when 1gm of water at 100oc freezer to ice at 0oC?
Answer:
Energy transferred when 1g of boiling water at 100oC cools to water at 0oC is as found in the above question is – 100cal
Now, latent heat change on changing the state from water to ice = 80cal/g
Hence, energy released when 1gm of water at 100oc freezes to ice at 0oC = 100 + 80 = 180cal
Question 9. Answer these. (ASI)
How much energy is released or absorbed when 1gm of steam at 100oc turns to ice at 0oC?
Answer:
Latent heat of vaporization = 540cal/g
Energy transferred when 1g of boiling water at 100oC cools to water at 0oC is – 100cal
Latent heat change on changing the state from water to ice = 80cal/g
Hence, energy released when 1gm of steam at 100oC turns to ice at 0oC = 540 + 100 + 80 = 720cal.
Question 10.
Explain the procedure of finding specific heat of solid experimentally. (AS1)
Answer:
The procedure of finding specific heat of solid experimentally is as follows : –
a. Take a calorimeter along with a stirrer.
b. Measure them in a weighing scale and let their mass be m1.
c. Fill one third of the volume of calorimeter with water and let it’s weight be m2 with temperature T1.
d. Take a few lead shots and place them in hot water and heat them up to a temperature 1000C. Let this temperature be T2.
e. Transfer the hot lead shots quickly into the calorimeter.
f. Then measure the temperature of water and lead shots as T3.
g. The mass of calorimeter along with content is measured as m3.
Now we have: –
Mass of the water = m2 – m1
Mass of the lead shots = m3 – m2
Specific heat of calorimeter = Sc
Specific heat of water = Sw
Specific Heat of lead shots = sl
Initial temperature of water = T1
Temperature of Lead shots = T2
Final temperature of the system = T3
h. We know from the method of mixtures that: –
Heat lost by the solid = Heat gain by the calorimeter + Heat gained by the water
⇒ 
⇒ 
= 
From the above formula we can find the specific heat of solid experimentally.
Question 11.
Covert 20oC into Kelvin scale. (AS1)
Answer:
We know that : –
Temperature in Kelvin = Temperature in Degree Celsius + 273
Hence, 20oC = 20 + 273 = 293K.
Question 12.
Your friend is asked to differentiate between evaporation and boiling. What questions could you ask to make him to know the differences between evaporation and boiling? (AS2)
Answer:
The questions that I ask my friend to make him know the differences between evaporation and boiling would be : –
a. Which phenomena take place at all temperatures?
b. Is evaporation a cooling process or warming process?
c. Which a surface phenomena?
Question 13.
What happens to the water when wet clothes dry’? (AS3)
Answer:
When wet clothes dry the liquid present on the surface of the clothes keeps escaping from the surface till the entire liquid disappears into the air by the process of evaporation. This process is aided when we have a windy day with dry atmosphere as it helps to carry the molecules away from the cloth more rapidly.
Question 14.
Equal amounts of water are kept in a cap and in a dish. Which will evaporate faster? Why? (AS3)
Answer:
We know that the rate of evaporation of a liquid depends on its surface area exposed, temperature and amount of vapour already present in the air.
Now when the temperature and amount of vapour already present in the air is constant then the rate solely depends upon the surface area exposed. The larger the surface area would be the more will be the number of water molecules escaping into the air and faster would be the rate of evaporation. Now between cap and dish, the dish has larger surface area and hence the water kept in the dish will evaporate faster.
Question 15.
Suggest an experiment to prove that the rate of evaporation of a liquid depends on its surface area and vapour already present in surrounding air. (AS3)
Answer:
An experiment to prove that the rate of evaporation of a liquid depends on its surface area is as follows: –
Take 10 ml of volatile liquid in a test-tube and another 10 ml of volatile liquid in the large dish. Observe the change in the volume of the liquid in both the cases. It would be found out that the liquid in the large dish had vanished much earlier than that in the test-tube which clearly implies that the rate of evaporation of a liquid depends on its surface area as the large dish has more surface area than the test-tube.
An experiment to prove that the rate of evaporation of a liquid depends on the vapour already present in surrounding air : –
Take a few drops of spirit in two Petri dishes separately. Keep one of the dishes containing spirit under a ceiling fan and switch on the fan. Keep another dish with its lid closed. Observe the quantity of spirit in both dishes after 7 minutes. It would be seen that the spirit which was in the petri dish had evaporated faster than the spirit which was in the other. This was because the ceiling fan was dispersing the vapour making the surrounding less humid while the closed lid leads to a more humid condition. Hence we could conclude that the rate of evaporation of a liquid depends on the vapour already present in surrounding air.
Question 16.
Place a Pyrex& ass llama with its mouth-down in a sauce pan full of water, in such a way Out the stern tube of the funnel is above the water or pointing upward into the air. Rest the edge of the bottom portion of the funnel on a nail or on a coin so that water can get under it. Place the pan on a stove and heat it till it begins to boil. Where do the bubbles form first? Why’? Can you ex plain how a natural geyser works using this experience. (AS4)
Answer:
We know the fact that the boiling point of water increases with increase in pressure. In this case, the bubbles start from the bottom of the sauce pan were we had put the nail or coin.
Similarly, in the geyser, boiling begins near the bottom and the bubbles that are raising above push the water out starting the process of eruption. This method could be treated as the laboratory demonstration of how a natural geyser functions.
Question 17.
Collect information about working of natural geyser and prepare a report. (AS4)
Answer:
Working of a natural geyser.
Geysers are generally associated with volcanic areas. As the water boils, the resulting pressure forces a superheated column of steam and water to the surface through the geyser’s internal plumbing. The heat needed for geyser formation comes from magma that needs to be close to the surface of the earth.
Geyser activity, like all hot spring activity, is caused by surface water gradually seeping down through the ground until it meets rock heated by magma. The geothermally heated water then rises back toward the surface by convection through porous and fractured rocks. Geysers differ from non-eruptive hot springs in their subterranean structure; many consist of a small vent at the surface connected to one or more narrow tubes that lead to underground reservoirs of water and pressure tight rock.
As the geyser fills, the water at the top of the column cools off, but because of the narrowness of the channel, convective cooling of the water in the reservoir is impossible. The cooler water above presses down on the hotter water beneath, not unlike the lid of a pressure cooker, allowing the water in the reservoir to become superheated, i.e. to remain liquid at temperatures well above the standard-pressure boiling point.
Ultimately, the temperatures near the bottom of the geyser rise to a point where boiling begins; steam bubbles rise to the top of the column. As they burst through the geyser’s vent, some water overflows or splashes out, reducing the weight of the column and thus the pressure on the water underneath. With this release of pressure, the superheated water flashes into steam, boiling violently throughout the column. The resulting froth of expanding steam and hot water then sprays out of the geyser vent.
Question 18.
Assume that heat is being supplied continuously to 2kg of ice at -5oC. You know that ice melts at 0oC and boils at 100oC Continue the heating till it starts boiling. Note the Immature every minute. Draw a graph between temperature and time using the values you get. What do you understand from the graph. Write the conclusion. (AS3)
Answer:
Experimental question can’t be explained theoretically need to perform the experiment to obtain the solution.
Question 19.
How do you appreciate the role of the higher specific heat of water in stabilizing atmospheric temperature dying winter and summer seasons? (AS6)
Answer:
Earth receives huge amount of heat energy from the Sun every day. With this heat, the Earth must have been heated beyond the level that it can withstand, but this is not actually happening because of the water bodies such as oceans, seas, lakes and rivers. They act as the store houses of heat energy from the Sun.
During the winter and summer, the water acts as balancing factor for controlling the temperature with its high specific heat.
During summer the water near the equator heats up faster and more than that near the poles as near the equator the amount of heat energy received is comparatively larger and hence circulation of water from the equator to the poles helps in maintaining the temperature of both the regions. Almost a similar phenomenon occurs during winter.
Question 20.
Suppose that 1l of water is heated for a certain time to rise and its temperature by 2oC. If 2l of water is heated for the same time, by how much will its temperature rise? (AS7)
Answer:
We know that: – Q = mS∆T
⇒ ∆T = 
⇒∆T is inversely proportional to the heat supplied.
⇒If the mass is greater than we get a change in temperature for the same amount of heat supplied.
Given the change in temperature when 1l(m1) of water is heated for a certain time = ∆T1 = 2oC
Let the change in temperature when 2l(m2) of water is heated for a certain time be ∆T2
Heat supplies and specific heat is constant for both the cases.
∴ 
⇒ 
⇒ ∆T2 = 
⇒∆T2 = 1 oC
Hence, if 2l of water is heated for the same time then 1 of temperature rise will take place.
Question 21.
What role does specific heat play in keeping a watermelon cool for a long time after removing it from a fridge on a hot day’? (AS7)
Answer:
The specific heat of watermelon is more than that of the surrounding air. Hence even after coming out of the refrigerator, it maintains it’s coldness for a long time as due to high specific heat the rate of heat loss to the surroundings is low.
Question 22.
If you are chilly outside the shower stall, why do you feel warm alter the bath if you stay in the bathroom? (AS7)
Answer:
We feel warm after we finish our bath under the shower. The reason for this could be that in the bathroom, the number of vapor molecules per unit volume is relatively greater than the number of vapour molecules per unit volume outside the bathroom. Hence, when we try to dry ourselves with a towel, the vapour molecules surrounding us condense on our skin. This condensation is what which makes us feel warm.