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Physics Case study (4 Marks)

Thermal Properties of Matter · MP Board (MPBSE) STD 11 Science (Madhya Pradesh - English Medium). 4 questions.

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Case study (4 Marks)

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Question 14 Marks
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 $\left({ }^{\circ} C \right)$ 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 $32^{\circ} F$ and $212^{\circ} F$, respectively, on the Fahrenheit scale and $0^{\circ} C$ and $100^{\circ} C$ 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. $PV =\mu RT$ where, $\mu$ is the number of moles in the sample of gas and $R$ is called universal gas constant: $R=8.31 J mol ^{-1} K^{-1}$ we have learnt that the pressure and volume are directly proportional to temperature: $PV \alpha T$. 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 $-273.15^{\circ} C$ 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 $T=t_c+273.15$
i. The SI unit of heat energy transferred is expressed in:
  1. The SI unit of heat energy transferred is expressed in:
  1. Joule (J)
  2. Kelvin (K)
  3. Newton (N)
  4. None of these
  1. Temperature is measured using:
  1. Thermometer
  2. Barometer
  3. Tachometer
  4. None of these
  1. 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
  1. What is heat energy.
  2. What is absolute zero temperature.
Answer
  1. (a) Joule (J)
  2. (a) Thermometer
  3. (a) $T = t_c + 273.15$
  4. Heat energy is the form of energy transferred between two or more systems or its surroundings due to temperature difference from higher temperature to lower temperature. The SI unit of heat energy transferred is expressed in joule (J).
  5. The absolute minimum temperature for an ideal gas at which pressure becomes zero is found to be $– 273.15^\circ C$ and is designated as absolute zero temperature. This is lowest temperature possible for ideal gas.
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Question 24 Marks
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
  1. Convection is possible in:
  1. Solids only
  2. Fluid only
  3. Both solid and fluid
  4. None of these
  1. Define latent heat of fusion and latent heat of vapourisation.
  2. Define process of natural convection.
  3. Differentiate between conduction and radiation.
Answer
  1. (c) Both a and b
  2. (b) Fluid only
  3. The heat required for conversion of solid state to liquid state without change in temperature is called the latent heat of fusion (Lf).
  4. The heat required for conversion of liquid state to solid state without change in temperature is called the latent heat of vaporisation (Lv).
  5. 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. Convection involves bulk transport of different parts of the fluid.
  6. Following are differentiate poin;
Sr No.
Conduction
Radiation
1
It requires medium to transfer heat.
It does not require medium to transfer heat
2
Heat transfer from one part to other part due to direct contact between each other
Heat can be transferred without any contact
3
Temperature difference is cause for transfer of heat
Any body having temperature higher than 0 can radiate energy
4
For example transfer of heat from one hot end of rod to other cold end
For example heat coming from sun to earth
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Question 34 Marks
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 $CO_2$) 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
  1. The change of state from solid to liquid is called:
  1. Melting
  2. Vaporization
  3. Sublimation
  4. None of these
  1. Define melting point and boiling point:
  2. What is sublimation?
  3. Define fusion process:
Answer
  1. (a) Calorimeter.
  2. (a) Melting.
  3. The change of state from solid to liquid is called melting process and temperature at which conversion of solid into liquid happens is called as melting point. The temperature at which the liquid and the vapour states of the substance coexist is called its boiling point.
  4. The change from solid state directly into vapour state without passing through the liquid state is called sublimation, and the substance is said to sublime.
  5. The change of state from liquid state to solid state is called as fusion process.
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Question 44 Marks
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
Answer
  1. (b) convection
  2. (d) all of the above
  3. (a) convection
  4. (a) increase
  5. (c) radiation
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