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A) -20° C to 0° C

B) 0° C to 100° C

Correct option is  C) 100° C

Correct option is  B) increase

B) density of ice is less than water

Correct option is  A) 0°C

Ways of heat transfer: conduction, convection and radiation.

[Note: heat ≡ heat energy. In the textbook, both the terms are used.]

Correct Answer is: (a) 4πkR²T / P

Area of spherical shell = 4πR².

Rate of heat flow = P = k(4πR²) T/d , where d = thickness of shell.

Correct Answer is: (c) 1/2

Let P = power radiated by the sun, R = radius of planet.

Energy received by planet = P / 4πd² x πR².

Energy radiated by planet = (4πR²) σT⁴.

For thermal equilibrium, P / 4πd² x  πR² = 4πR² σT⁴.

or T⁴ ∝ 1/d²

or T ∝ 1 /d^1/2

or T ∝ d^-1/2 . 

Correct Answer is; (a) Σ ∝ T⁴ , (c) Σ ∝ θ²

Let R = radius of the sun, d = distance of the earth from the sun.

Power radiated by the sun = (4πR²) σT⁴ =P. 

Energy received per unit area per second normally on the earth 

= Σ = P/4πd² 

= 4πR²σT⁴ / 4πd² 

= (σT⁴) (R/d)² 

= 1/4 σT⁴ (2R/d)²

Angle subtended by the sun at the earth = θ 2R/d.

or Σ = constant x T⁴ x θ².

1) The metal piece is colder than the wooden piece. 

2) Because more heat energy flows out of our body so metal piece gives coldness to our body, than wooden piece.

Procedure: 

Take a piece of wood and a piece of metal and keep them in fridge or ice box. Observation : When we touch both of them we feel that metal piece is colder than the wooden piece. 

Explanation : 

This is due to more energy flow out of our body when we touch the metal piece as compared with wooden piece. 

• The degree of coldness of metal is greater than that of the wooden piece. 
• The degree of hotness or coldness is called temperature. 
• From this example, we say metal piece is at a lower temperature compared to wooden piece.

Correct option is: A) remains constant

A) remains constant

Correct option is: B) liquid phase at constant temperature

Procedure : 

Take two glass tumblers and fill one of them with hot water and another with cold water. 

Explanation & Observation : 

1) When we place a thermometer inside the hot water the mercury level of thermometer rises from initial position due to heat transferred from hotter body (hot water) to colder body (mercury in thermometer). 

2) When we place the thermometer inside the cold water the mercury level comes down from its initial position due to transfer of heat from mercury (hotter body) to water (colder body). 

Conclusion : 

• Heat is a form of energy that flows from a body at higher temperature to a body at lower temperature until the temperature remains same for two bodies that is called thermal equilibrium. 
• In the above case, the steadiness of mercury column shows that thermal equilibrium is achieved. That reading of mercury column gives temperature. 
• Thus temperature is a measure of thermal equilibrium.

Procedure : 

Take two bowls one with hot water and second with cold water. Gently sprinkle food colour on the surface of the water in both bowls.

Observation : 

We will observe the jiggling of grains of food colour in hot water is more when compared to jiggling in cold water. 

Explanation : 

• We know kinetic energy depends on speed motion of particles. 
• So the kinetic energy of hotter body is greater than that of colder body. 
• Thus the temperature of a body is an indicator of average kinetic energy of molecules of that body. 

Conclusion : 

Therefore average kinetic energy of molecules is directly proportional to absolute temperature.

1. Radiation of heat takes place from many objects in nature such as trees, mountains, stones and roads. 

2. A camera has been developed which uses these radiations to make our surroundings visible even at night. This is called infrared camera. 

3. It is used to keep watch on the movements of the enemy during the night. 

4. It is also used to track the movements of animals in the wild.

1. Thermoware containers keep food hot. These containers consist two boxes fitted one inside the other.

2. The outer box is made up of plastic while the inner one is made up of a shiny metal, there is air between the two boxes. 

3. Air is a bad conductor of heat. Thus, heat is not lost by either conduction or convection. Also, the shiny inner surface prevents heat loss due to radiation. 

4. The container has a plastic lid. This also prevents any transfer of heat.

Temperature : 

The measure of hotness or coldness of a body is called temperature.

1. Two bodies should have difference in temperature. 

2. They (two bodies) are in thermal contact with each other.

3. When the bodies have equal temperature there is no transfer of heat energy.

Water transfers heat energy in the mode of convection.

No, when the bodies are in thermal equilibrium there is no transfer of heat energy.

D) evaporation

When two bodies attain the same degree of hotness or coldness then they are said to be in thermal equilibrium.

If two different systems, A and B, (thermal contact) are in thermal equilibrium individually with another system C, then the systems A and B are in thermal equilibrium with each other.

1. Due to the temperature difference between the two bodies which are in thermal contact.

2. Now heat energy transfers from hot body to cold body until they attain same temperature.

Correct option is: B) condensation

B) condensation

B) condensation

1. Yes, the principle of calorimetry, means heat loss by hot body is equal to heat gained by cold body. 

2. This means that when heat energy flows out of our body we feel the coldness and when heat energy enters our body we feel hotness.

Due to more heat energy loss by our body when touches the metal piece compared to the wooden piece. 

In other way we say degree of coldness of the metal piece is greater than that of. the wooden piece.

1) No, the volume of ice is greater than volume of water. 

2) Water expands on freezing. 

3) That means density of ice is less than density of water.

The factors effecting boiling are 

I) Pressure : 

1. The boiling point of pure water at one atmospheric pressure is 100°C. 

2. Water boils at a temperature higher than 100°C, if the atmospheric pressure is higher than one atmosphere pressure, and boils at a temperature lower than 100°C, if the atmospheric pressure is less than 1 atmosphere.

II) Impurities : 

The boiling point of liquid increases by the addition of impurities to it. If a little common salt is added to water, the water boils at a temperature higher than 100°C.

1. The specific heat of water is very high. It is about five times as that of sand. 

2. Hence the heat energy required for the same rise in temperature by certain mass pf water will be nearly five times than that required by same mass of sand. 

3. Similarly, a certain mass of water will give out nearly five times more heat energy than that given by sand of the same mass for the same fall in temperature.

4. As such, sand (or earth) gets heated or cooled more rapidly as compared to water under similar conditions. 

5. Thus, a large difference in temperature is developed between the land and sea due to which land and sea breezes are formed. 

6. These breezes make the climate near seashore moderate.

1. In the absence of water, if on a cold winter night, the atmospheric temperature falls below 0°C, the water in the fine capillaries of plants will freeze, so the veins will burst due to the increase in volume of water on freezing. 

2. As a result, plants will die and the crop will be destroyed. 

3. In order to save crop on such cold nights, farmers fill their field with water because water has high specific heat, so it does not allow the temperature in the plants of surrounding area to fall up to 0°C.

1. When we heat solids the vibrations and movement of molecules will increase. 

2. The temperature of the object increases. 

3. The distance between molecules will increase.

(a) begin to move faster

Melting: The process of converting solid into liquid.

The ice has less density compared to water. So it forms a layer on the top of water which prevents the solidification of water.