Thermal Properties of Matter Physics - Thermal Properties of Matter

On a hilly region, water boils at 95°C. The temperature expressed in fahrenheit is:

Water of volume 2 litre in a container is heated with a coil of 1 kW at 27°C. The lid of the container is open and energy dissipates at the rate of 160 Js-. In how much time temperature will rise from 27°C to 77°C? [Given specific heat of water = 4.2kJ/ kg]

The density of a substance at 0°C is 10g/cc and at 100°C, its density is 9.7g/cc. The coefficient of linear expansion of the substance is:

If m mass of a substance undergoes a phase change, then amount of heat required will be:

Suppose there is a hole in a copper plate. Upon heating the plate, diameter of hole would:

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 questions based on the P-T phase diagram of carbon dioxide

1. At what temperature and pressure can the solid, liquid and vapour phases of CO₂ co-exist in equilibrium ?
2. What is the effect of decrease of pressure on the fusion and boiling point of CO₂?
3. What are the critical temperature and pressure for CO₂? What is their significance?
4. Is CO₂ solid, liquid or gas at (a) –70 °C under 1 atm, (b) –60 °C under 10 atm, 15 °C under 56 atm?

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)?

A blacksmith fixes iron ring on the rim of the wooden wheel of a horse cart. The diameter of the rim and the iron ring are 5.243 m and 5.231 m, respectively at 27 °C. To what temperature should the ring be heated so as to fit the rim of the wheel?

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.

Calculate the heat of combustion of coal, when 10 gm of coal, on burning raises the temperature of 2kg of water from 20°C to 55°C.

A copper block of mass 2.5kg is heated in a furnace to a temperature of 500°C and then placed on a large ice block. What is the maximum amount of ice that can melt? (Specific heat of copper = 0.39 J g^–1 K^–1; heat of fusion of water = 335 J g^–1 ).

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.

A pan filled with hot food cools from 94 °C to 86 °C in 2 minutes when the room temperature is at 20 °C. How long will it take to cool from 71 °C to 69 °C?

Read the passage given below and answer the following questions from (i) to (v).
A system is said to be isolated if no exchange or transfer of heat occurs between the system and its surroundings. When different parts of an isolated system are at different temperature a quantity of heat transfers from the part at higher temperature to the part at lower temperature. The heat lost by the part at higher temperature is equal to the heat gained by the part at lower temperature. Calorimetry means measurement of heat. When a body at higher temperature is brought in contact with another body at lower temperature, the heat lost by the hot body is equal to the heat gained by the colder body, provided no heat is allowed to escape to the surroundings. A device in which heat measurement can be done is called a calorimeter. It consists of a metallic vessel and stirrer of the same material, like copper or aluminium. The vessel is kept inside a wooden jacket, which contains heat insulating material. Matter normally exists in three states: solid, liquid and gas. A transition from one of these states to another is called a change of state. Two common changes of states are solid to liquid and liquid to gas (and, vice versa). These changes can occur when the exchange of heat takes place between the substance and its surroundings. The change of state from solid to liquid is called melting and from liquid to solid is called fusion. It is observed that the temperature remains constant until the entire amount of the solid substance melts. That is, both the solid and the liquid states of the substance coexist in thermal equilibrium during the change of states from solid to liquid. The temperature at which the solid and the liquid states of the substance is in thermal equilibrium with each other is called its melting point. The change of state from liquid to vapour (or gas) is called vaporisation. It is observed that the temperature remains constant until the entire amount of the liquid is converted into vapour. That is, both the liquid and vapour states of the substance coexist in thermal equilibrium, during the change of state from liquid to vapour. The temperature at which the liquid and the vapour states of the substance coexist is called its boiling point. The change from solid state to vapour state without passing through the liquid state is called sublimation, and the substance is said to sublime. Dry ice (solid CO₂) sublimes, so also iodine. During sublimation both the solid and vapour states of a substance coexist in thermal equilibrium.

1. Device used for measurement of heat is:

1. Calorimeter
2. Thermometer
3. Both a and b
4. No one of these

2. The change of state from solid to liquid is called:

1. Melting
2. Vaporization
3. Sublimation
4. None of these

3. Define melting point and boiling point:
4. What is sublimation?
5. Define fusion process:

Read the passage given below and answer the following questions from (i) to (v).
We can say that heat is the form of energy transferred between two (or more) systems or a system and its surroundings by virtue of temperature difference. The SI unit of heat energy transferred is expressed in joule (J) while SI unit of temperature is Kelvin (K), and degree Celsius (°C) is a commonly used unit of temperature. When an object is heated, many changes may take place. Its temperature may rise; it may expand or change state. A measure of temperature is obtained using a thermometer. Many physical properties of materials change sufficiently with temperature. Some such properties are used as the basis for constructing thermometers. The two familiar temperature scales are the Fahrenheit temperature scale and the Celsius temperature scale. The ice and steam point have values 32°F and 212 °F, respectively, on the Fahrenheit scale and 0 °C and 100°C on the Celsius scale. On the Fahrenheit scale, there are 180 equal intervals between two reference points, and on the Celsius scale, there are 100. A relationship for converting between the two scales may be obtained from a graph of Fahrenheit temperature (t_F) versus Celsius temperature (t_C) in a straight line. When temperature is held constant, the pressure and volume of a quantity of gas are related as PV = constant. This relationship is known as Boyle’s law. When the pressure is held constant, the volume of a quantity of the gas is related to the temperature as V/T = constant. This relationship is known as Charles’ law. Low-density gases obey these laws, which may be combined into a single relationship. PV = μRT where, μ is the number of moles in the sample of gas and R is called universal gas constant: R = 8.31J mol^-1 K^-1 we have learnt that the pressure and volume are directly proportional to temperature: PVαT. This relationship allows a gas to be used to measure temperature in a constant volume gas thermometer. The absolute minimum temperature for an ideal gas at which pressure becomes zero is found to be – 273.15°C and is designated as absolute zero. Absolute zero is the foundation of the Kelvin temperature scale or absolute scale temperature. The size of unit in Kelvin and Celsius temperature scales is the same. So, temperature on these scales are related by T = t_c + 273.15

1. The SI unit of heat energy transferred is expressed in:

1. Joule (J)
2. Kelvin (K)
3. Newton (N)
4. None of these

2. Temperature is measured using:

1. Thermometer
2. Barometer
3. Tachometer
4. None of these

3. Relation between Kelvin (T) and Celsius temperature (tc) scale is given by:

1. T = t_c + 273.15
2. T = t_c – 273.15
3. T = t_c
4. None of these

4. What is heat energy.
5. What is absolute zero temperature.

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

A brass rod of length 50cm and diameter 3.0mm is joined to a steel rod of the same length and diameter. What is the change in length of the combined rod at 250°C, if the original lengths are at 40.0°C? Is there a ‘thermal stress’ developed at the junction? The ends of the rod are free to expand (Co-efficient of linear expansion of brass = 2.0 × 10^–5 K^–1, steel = 1.2 × 10^–5 K^–1).

A brass wire 1.8m long at 27°C is held taut with little tension between two rigid supports. If the wire is cooled to a temperature of –39°C, what is the tension developed in the wire, if its diameter is 2.0mm? Co-efficient of linear expansion of brass = 2.0 × 10^–5 K^–1; Young’s modulus of brass = 0.91 × 1011Pa.

In an experiment on the specific heat of a metal, a 0.20kg block of the metal at 150°C is dropped in a copper calorimeter (of water equivalent 0.025kg) containing 150cm³ of water at 27°C. The final temperature is 40°C. Compute the specific heat of the metal. If heat losses to the surroundings are not negligible, is your answer greater or smaller than the actual value for specific heat of the metal?

Gas	Molar specific heat (Cv) (cal mo1–1 K–1)
Hydrogen	4.87
Nitrogen	4.97
Oxygen	5.02
Nitric oxide	4.99
Carbon monoxide	5.01
Chlorine	6.17

 The measured molar specific heats of these gases are markedly different from those for monatomic gases. Typically, molar specific heat of a monatomic gas is 2.92 cal/ mol K. Explain this difference. What can you infer from the somewhat larger (than the rest) value for chlorine?

Temperature	Pressure thermometer A	Pressure thermometer B
Triple-point of water	1.250 × 105Pa	0.200 × 105Pa
Normal melting point of sulphur	1.797 × 105Pa	0.287 × 105Pa

What is the absolute temperature of normal melting point of sulphur as read by thermometers A and B?

What do you think is the reason behind the slight difference in answers of thermometers A and B? (The thermometers are not faulty). What further procedure is needed in the experiment to reduce the discrepancy between the two readings?