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Procedure : 

1. Take small ice cube in a beaker. Insert the thermometer in the beaker. 

2. Now start heating the beaker and note down readings of thermometer every one minute till the ice completely melts and gets converted into water. 

3. Before heating the temperature of ice is 0° C or less than 0° C.

Observation :

1. We will observe that the temperature of ice at the beginning is equal to or below 0°C. 

2. If the temperature of ice is below 0°C, it goes on changing till it reaches 0° C. 

3. When ice starts melting, we will observe no change in temperature though you are supplying heat continuously.

Explanation : 

1. Given heat energy is used to break the bonds (H₂O) in ice and melts. 

2. So, temperature is constant while melting.

Conclusion : 

1. This process is called melting. In this process heat converts solid phase to liquid phase. 

2. The temperature of the substance does not change until all the ice melts and converts into water. 

3. The heat given to melting is called latent heat of fusion. 

4. The heat required to convert 1 gm of solid completely to liquid at constant temperature is called “latent heat of fusion”.

m = 5 gm; L_f = 80 cal/g

The amount of heat absorbed Q = ML_f = 5 × 80 = 400 cal /g.

The temperature of boiling water in the Celsius scale of temperature is C (100/373/212/32).

The SI unit of heat is Joule/ Celsius.

(1) Heat is transferred from a hot object to a cold object.

(2) This process shows the principle of heat exchange.

(3) In this process, the cold object gains heat energy and the hot object loses energy. If a system of two objects is isolated from the surroundings, heat energy lost by the hot object = heat energy gained by the cold object.

(4) This principle is used to measure the specific heat capacity of a substance.

1. True

2. False

3.False

Explanation:

(1) Water expands as its temperature decreases from 4 °C to 0 °C. Water is converted into ice at 0 °C. The density of water is more than that of ice. Fishes can remain alive in the water (at 4 °C) below the ice.

(2) At high altitudes, atmospheric pressure is low and hence water boils at a temperature lower than its normal boiling point. Therefore, the time required for cooking food is more at higher altitudes.

(3) Water expands while freezing. Hence, the water present in the crevices of the rocks exerts a tremendous pressure on the rocks, while freezing. Therefore, the cliffs fall.

(4) Water expands while freezing. Hence, the water in the tube exerts a large pressure on the tube, while freezing. Therefore, the tube carrying water breaks.

If we rub our palms vigorously or rubbing a metal strip of an iron nail on a stone several time that is produced. There are the examples to illustrate that heat can be generated from the energy of motion.

1. Heat : 

• Heat is a form of energy 
• Heat energy depends upon the speed of the particles, the number of particles and size or mass and the type of particles in an object. 
• It is the sum of energies of all molecules,
•  SI unit of heat is Joule. 

2. Temperature : 

• Temperature is a measure of the degree of hot or cold . lt is a number that ,is related to energy, but it is not energy itself. 
•  Temperature does not depend on the size or mass of an object. For example, temperature of a small cup of water is the same as the temperature of a tub of water. 
•  It is the average kinetic energy of the molecules. 
• SI unit of temperature is Kelvin.

The three effects produced by heat are 

1. Increase in temperature 

2. Thermal expansion 

3. Change in physical state 

4. Change in chemical change

The total kinetic energy of all the molecules in a substance is called heat. The SI unit of heat is Joule (J)

The three effect produced by heat are 

1. Increase in temperature 

2. Thermal expansion 

3. Change in physical state 

4. Chemical change

In industries, hot water or molten liquid is transferred from one place to another through metal pipelines. The expansion and contraction might bend or break the pipe. To over come this, these metal pipelines are provided with loops at regular intervals. The expansion of pipeline causes the size of loop to increase slightly so pipe does not break.

Thermal expansion of bimetallic strips used as a heat operated switch in the circuit of automatic equipments like iron box, fire alarms, electric heater etc. Some thermometers work on the principle of expansion of liquids In automobile engines useful work is done by the expansion of gases.

The amount of heat needed to raise the temperature of 1 kg of silver by 1 °C is 0.056 kcal.

A hot solid is put in water in a calorimeter. The mixture is stirred continuously and the maximum temperature of the mixture is measured with a thermometer. Heat exchange between the hot solid, water and calorimeter results in sill bodies attaining the same temperature after some time. Hence, according to the principle of heat exchange, heat lost by the solid = heat gained by the water in the calorimeter + heat gained by the calorimeter.

Now, heat lost by the solid (Q) = mass of the solid × its specific heat capacity × decrease in its temperature, heat gained by the water (Q₁) = mass of the water × its specific heat capacity × increase in its temperature and heat gained by the calorimeter (Q₂) = mass of the calorimeter × its specific heat capacity × increase in its temperature.

Heat lost by the hot object = heat gained by the calorimeter + heat gained by the water. Q = Q₂ + Q₁ Using this equation, the specific heat capacity of the solid can be determined (measured) when the other quantities are known.

There are three commonly used scales of temperature:

1. Celsius scale of temperature °C 

2. Fahrenheit scale of temperature °F 

3. Kelvin scale of temperature K

Correct Answer is: (c)

Correct Answer is: (c) 1 + 2/f

Units of heat: joule, erg, calorie, kilocalorie.

The amount of heat necessary to raise the temperature of 1 g of water by 1 °C from 14.5 °C to 15.5 °C is called one calorie.

1 kilocalorie = 10³ calories.

Correct answer is (c) ice cubes

1 kilocalorie = 4.18 × 10³ joules.

1 kilocalorie = 4.18 × 10¹⁰ ergs.

Correct answer is (d) Kelvin

The amount of heat necessary to raise the temperature of 1 kg of water by 1 °C from 14.5 °C to 15.5 °C is called one kilocalorie.

Correct answer is  (b) Joule

Correct Answer is: (a) f₁ - f₂ / f₂t₁ - f₁t₂

Correct Answer is: (c) 1.6 W 

Let R = total thermal resistance of the ring,

ΔT = difference in temperature between A and B.

For θ = 180°, two sections of resistance R/2 each are in parallel.

Equivalent resistance = R/4.

Rate of total heat flow = I₁ = 1.2 = ΔT/R/4

or 0.3 = ΔT/R

For θ = 90°, two sections of resistances R/4 and 3R/4 are in parallel.

Equivalent resistance = (R/4)(3R/4) / R/4 

= 3R/4 

= 3R/16 . 

Rate of total heat flow

I₂ = ΔT/3R/16 W 

= 16/3 (ΔT/R) W 

= 16/3 x 0.3 W 

= 1.6 W.

Correct Answer is: (b, c)

The horizontal parts of the curve, where the system absorbs heat at constant temperature, must depict changes of state. Here the latent heats are proportional to the lengths of the horizontal parts. In the sloping parts, specific heat capacity is inversely proportional to the slopes.

1. When ice cubes are placed in a beaker, ice starts melting. The heat required for melting is absorbed from the surrounding air and also from the beaker to some extent.

Hence, the temperature of the air and beaker falls.

2. The capacity of air to hold water vapour depends upon the temperature of the air, and this capacity decreases as the temperature decreases. At a certain low temperature, the surrounding air becomes saturated with water vapour present in it. As the temperature falls further, the air is unable to hold all the water vapour.

Hence, the extra water vapour starts condensing on the cold outer surface of the beaker in the form of minute drops. Therefore, the outer surface of the beaker containing ice cubes becomes wet in a short while.

Absolute humidity:

1. Absolute humidity is the mass of water vapour present in a unit volume of air.

2. It is commonly expressed in kg/m³.

Relative humidity:

1. Relative humidity is the ratio of the mass of water vapour in a given volume of air at a given temperature to the mass of water vapour required to saturate the same volume of air at the same temperature.

2. It does not have unit.

(d) Assertion is false, but the reason is true

1. True

2. False 

Correct statement: The dimensions of a substance are increased if the temperature of the substance is increased.

3. False 

Correct statement: The process of converting a substance from solid to gas is called sublimation.

4. False 

Correct statement: Convection is the process by which the thermal energy flows in liquids and gases.

5. True

6. False 

Correct statement: In a thermos flask, the silvered walls reflect radiated heat back to the liquid in the bottle.

1. heat capacity of water 

2. Specific heat capacity 

3. temperature of an object constant 

4. deposition 

5. increase 

6. decrease

Thermostat functions both as the sensor and the controller of a thermal system.

Central heater in a room, air conditioner, water heater, oven and refrigerators.