Thermal Properties of Matter Physics - Thermal Properties of Matter

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At NTP, water boils at 100°C. Deep down the mine, water will boil at a temperature.

The amount of heat that a body can absorb by radiation:

The rates of cooling of two different liquids put in exactly similar calorimeters and kept in identical surroundings are the same if:

Answer the following : The triple-point of water is a standard fixed point in modern thermometry. Why? What is wrong in taking the melting point of ice and the boiling point of water as standard fixed points (as was originally done in the Celsius scale)?

Answer the following : There were two fixed points in the original Celsius scale as mentioned above which were assigned the number 0°C and 100°C respectively. On the absolute scale, one of the fixed points is the triple-point of water, which on the Kelvin absolute scale is assigned the number 273.16 K. What is the other fixed point on this (Kelvin) scale?

Answer the following: The absolute temperature (Kelvin scale) T is related to the temperature tc on the Celsius scale by tc = T – 273.15.

Answer the following : The triple-point of water is a standard fixed point in modern thermometry. Why? What is wrong in taking the melting point of ice and the boiling point of water as standard fixed points (as was originally done in the Celsius scale)?

Explain why: Heating systems based on circulation of steam are more efficient in warming a building than those based on circulation of hot water.

Explain why: The earth without its atmosphere would be inhospitably cold.

Explain why: A body with large reflectivity is a poor emitter.

Two bodies of specific heats and C, having same heat capacities are combined to form a single composite body. What is the specific heat of the composite body?

Is the bulb of a thermometer made of diathermic or adiabatic wall?

Explain why: An optical pyrometer (for measuring high temperatures) calibrated for an ideal black body radiation gives too low a value for the temperature of a red hot iron piece in the open, but gives a correct value for the temperature when the same piece is in the furnace.

Explain why: A brass tumbler feels much colder than a wooden tray on a chilly day.

Name the three modes of transfer of heat from one object to other. Also, cite one example for each one of them.

A body cools from 80 °C to 50 °C in 5 minutes. Calculate the time it takes to cool from 60°C to 30 °C. The temprature of the surroundings is 20°C.

Answer the following:
What is the temperature of the triple-point of water on an absolute scale whose unit interval size is equal to that of the Fahrenheit scale?

Read the passage given below and answer the following questions from (i) to (v). The amount of heat per unit mass transferred during change of state of the substance is called latent heat of the substance for the process. For example, if heat is added to a given quantity of ice at –10°C, the temperature of ice increases until it reaches its melting point (0°C). At this temperature, the addition of more heat does not increase the temperature but causes the ice to melt, or changes its state. Once the entire ice melts, adding more heat will cause the temperature of the water to rise. The latent heat for a solid to liquid state change is called the latent heat of fusion (Lf), and that for a liquid-gas state change is called the latent heat of vaporisation (Lv). These are often referred to as the heat of fusion and the heat of vaporisation. We have seen that heat is energy transfer from one system to another or from one part of a system to another part, arising due to temperature difference. What are the different ways by which this energy transfer takes place? There are three distinct modes of heat transfer: conduction, convection and radiation Conduction is the mechanism of transfer of heat between two adjacent parts of a body which are direct in contact because of their temperature difference. Suppose, one end of a metallic rod is put in a flame, the other end of the rod will soon be so hot that you cannot hold it by your bare hands. Here, heat transfer takes place by conduction from the hot end of the rod through its different parts to the other end. Gases are poor thermal conductors, while liquids have conductivities intermediate between solids and gas.Convection is a mode of heat transfer by actual motion of matter. It is possible only in fluids. Convection can be natural or forced. In natural convection, gravity plays an important part. When a fluid is heated from below, the hot part expands and, therefore, becomes less dense. Because of buoyancy, it rises and the upper colder part replaces it. This again gets heated, rises up and is replaced by the relatively colder part of the fluid. The process goes on. This mode of heat transfer is evidently different from conduction. Convection involves bulk transport of different parts of the fluid. Conduction and convection require some material as a transport medium. These modes of heat transfer cannot operate between bodies separated by a distance in vacuum. But the earth does receive heat from the Sun across a huge distance. Similarly, we quickly feel the warmth of the fire nearby even though air conducts poorly and before convection takes some time to set in. The third mechanism for heat transfer needs no medium; it is called radiation and the energy so transferred by electromagnetic waves is called radiant energy.

1. Which of the following heat transfer mode needs medium?

1. Conduction
2. Convection
3. Both a and b
4. Radiation

2. Convection is possible in:

1. Solids only
2. Fluid only
3. Both solid and fluid
4. None of these

3. Define latent heat of fusion and latent heat of vapourisation.
4. Define process of natural convection.
5. Differentiate between conduction and radiation.

Read the passage given below and answer the following questions from (i) to (v). The figure shows the different modes of transfer of heat, heat transfer is defined as the movement of heat across the border of the system due to a difference in temperature between the system and its surroundings. The temperature difference exists between the two systems, heat will find a way to transfer from the higher to the lower system.

1. The sea breeze is caused by:
   1. conduction
   2. convection
   3. radiation
   4. none of these
2. At what factor heat absorbed on radiation by the body depends on?
   1. distance between body
   2. source of heat
   3. its color
   4. all of the above
3. When heat is transferred by molecular collision, it is referred to as heat transfer by:
   1. convection
   2. conduction
   3. radiation
   4. convection and radiation
4. Thermal conductivity of air with rise in temperature:
   1. increase
   2. decrease
   3. constant
   4. none of these
5. Mass transfer does not take place in:
   1. conduction
   2. convection
   3. radiation
   4. none of these