40 Lecture

What is the unit of specific heat capacity?

a. J

b. J/K

c. J/kg

d. J/(kg.K)

Answer: d. J/(kg.K)

Which of the following is an example of a good thermal conductor?

a. Air

b. Glass

c. Aluminum

d. Rubber

Answer: c. Aluminum

Which law of thermodynamics states that heat flows from hotter to colder objects?

a. Zeroth law of thermodynamics

b. First law of thermodynamics

c. Second law of thermodynamics

d. Third law of thermodynamics

Answer: c. Second law of thermodynamics

Which of the following is an example of a reversible process?

a. Melting of ice

b. Burning of coal

c. Friction

d. Explosions

Answer: a. Melting of ice

What happens to the internal energy of a system during an adiabatic process?

a. It remains constant

b. It increases

c. It decreases

d. It becomes zero

Answer: a. It remains constant

Which of the following statements is true for an isothermal process?

a. The temperature of the system remains constant

b. The pressure of the system remains constant

c. The volume of the system remains constant

d. The internal energy of the system remains constant

Answer: a. The temperature of the system remains constant

The specific heat capacity of water is higher than that of iron. Which means:

a. It takes more heat energy to increase the temperature of water than iron

b. It takes less heat energy to increase the temperature of water than iron

c. Water and iron require the same amount of heat energy to increase their temperature

d. None of the above

Answer: a. It takes more heat energy to increase the temperature of water than iron

The amount of heat required to raise the temperature of a substance by one degree Celsius is called:

a. Heat energy

b. Internal energy

c. Thermal energy

d. Specific heat capacity

Answer: d. Specific heat capacity

Which of the following statements is true for an adiabatic process?

a. No heat is added or removed from the system

b. The temperature of the system remains constant

c. The volume of the system remains constant

d. The pressure of the system remains constant

Answer: a. No heat is added or removed from the system

Which of the following is an example of a good thermal insulator?

a. Glass

b. Rubber

c. Aluminum

d. Wool

Answer: d. Wool

What is thermal expansion? Give an example of a material that shows significant thermal expansion.

Answer: Thermal expansion is the tendency of a substance to expand or contract in response to changes in temperature. An example of a material that shows significant thermal expansion is metal. Metals expand when heated and contract when cooled, which can cause problems in machinery and structures.

What is thermal conductivity? Explain how it is related to heat transfer.

Answer: Thermal conductivity is the ability of a material to conduct heat. It is related to heat transfer in that materials with higher thermal conductivity transfer heat more easily than materials with lower thermal conductivity. This is because materials with higher thermal conductivity allow heat to flow through them more easily.

What is the difference between specific heat and heat capacity?

Answer: Specific heat is the amount of heat required to raise the temperature of one gram of a substance by one degree Celsius. Heat capacity, on the other hand, is the amount of heat required to raise the temperature of an entire object by one degree Celsius. Heat capacity is therefore dependent on the mass of the object, while specific heat is not.

What is convection? Give an example of convection in action.

Answer: Convection is the transfer of heat through the movement of fluids. An example of convection in action is the heating of a room through a radiator. The warm air rises from the radiator and is replaced by cooler air, creating a cycle of hot and cold air that circulates through the room.

What is the greenhouse effect? How does it relate to heat transfer?

Answer: The greenhouse effect is the process by which certain gases in the Earth's atmosphere trap heat, causing the Earth's surface to become warmer. This is similar to how a greenhouse works, as it traps heat inside to keep plants warm. The greenhouse effect relates to heat transfer because it involves the transfer of heat from the Earth's surface to the atmosphere.

What is the difference between a conductor and an insulator?

Answer: A conductor is a material that easily conducts heat, while an insulator is a material that does not conduct heat well. This means that conductors allow heat to flow through them easily, while insulators resist the flow of heat.

What is a thermocouple? How is it used to measure temperature?

Answer: A thermocouple is a device that measures temperature by producing a voltage proportional to the temperature difference between two points. It consists of two wires made of different metals that are joined at one end. When the joined end is exposed to heat, it produces a voltage that can be measured to determine the temperature.

What is the difference between conduction, convection, and radiation?

Answer: Conduction is the transfer of heat through direct contact between two objects. Convection is the transfer of heat through the movement of fluids. Radiation is the transfer of heat through electromagnetic waves.

What is the first law of thermodynamics?

Answer: The first law of thermodynamics, also known as the law of conservation of energy, states that energy cannot be created or destroyed, only transferred or converted from one form to another.

What is an adiabatic process?

Answer: An adiabatic process is a process in which no heat is exchanged between the system and its surroundings. This means that the temperature of the system changes without any input or output of heat. An example of an adiabatic process is the compression or expansion of a gas in a closed container.

Heat – II

Heat is a form of energy that is transferred from one object or system to another due to a difference in temperature. In the previous article, we discussed the basic concepts of heat such as thermal expansion, specific heat, thermal conductivity, and the first law of thermodynamics. In this article, we will discuss more advanced topics related to heat, including the second law of thermodynamics, heat engines, and entropy.

The Second Law of Thermodynamics

The second law of thermodynamics states that the total entropy of an isolated system always increases over time. Entropy is a measure of the disorder or randomness in a system. For example, a gas in a container will naturally spread out and fill the entire container, which increases the entropy of the system. Conversely, a gas that is compressed into a smaller volume will have a lower entropy. The second law of thermodynamics has several important implications. First, it explains why heat always flows from hot to cold objects. In a closed system, heat will always spontaneously flow from the hotter object to the colder object until they reach the same temperature, at which point there is no more heat transfer. The second law also explains why perpetual motion machines are impossible. Perpetual motion machines are machines that can supposedly generate energy indefinitely without any external input. However, they violate the second law of thermodynamics because they would have to create a decrease in entropy, which is impossible. Heat Engines A heat engine is a device that converts thermal energy into mechanical energy. Most heat engines operate using the principles of the Carnot cycle, which consists of four steps: Adiabatic compression: The gas is compressed without any heat entering or leaving the system. Isothermal compression: The gas is compressed further while maintaining a constant temperature, so that heat is absorbed from the surroundings. Adiabatic expansion: The gas expands without any heat entering or leaving the system. Isothermal expansion: The gas expands further while maintaining a constant temperature, so that heat is released to the surroundings. The efficiency of a heat engine is defined as the ratio of the mechanical work output to the heat input. According to the second law of thermodynamics, the efficiency of a heat engine cannot be 100%. In fact, the maximum theoretical efficiency of a heat engine operating between two temperatures T1 and T2 is given by: Efficiency = 1 - (T2 / T1) Entropy Entropy is a measure of the disorder or randomness in a system. The second law of thermodynamics states that the total entropy of an isolated system always increases over time. This means that in any natural process, there will always be an increase in the entropy of the system and its surroundings. Entropy is related to the concept of irreversibility. A reversible process is one that can be reversed by making infinitesimal changes to the system, while an irreversible process cannot be reversed. In an irreversible process, the total entropy of the system and its surroundings increases. The concept of entropy has many applications in physics and engineering. For example, it can be used to analyze the efficiency of heat engines, the behavior of gases, and the properties of materials. It also plays an important role in understanding the behavior of black holes and the universe as a whole. Conclusion Heat is a fundamental concept in physics and has many practical applications in engineering and technology. The second law of thermodynamics, heat engines, and entropy are important concepts that help us understand the behavior of heat and its relationship to other forms of energy. By studying these concepts, we can develop more efficient heat engines, better insulation materials, and a deeper understanding of the physical universe.