# 41 Lecture

## Heat – III

Heat is a form of energy that is transferred between systems or objects that are at different temperatures. It always flows from a hotter object to a colder object. In physics, heat is considered to be a type of energy that is transferred by a m

## Important Mcq's Midterm & Finalterm Prepration Past papers included

What is the SI unit of heat?

A) Kelvin (K)

B) Joule (J)

C) Watt (W)

D) Celsius (°C)

Which of the following is a good conductor of heat?

A) Wood

B) Plastic

C) Copper

D) Rubber

Which law of thermodynamics describes the relationship between temperature, energy, and entropy?

A) First law

B) Second law

C) Third law

D) None of the above

Which of the following is an example of convection?

A) Heat transfer through a metal rod

B) Heat transfer through a vacuum

C) Heat transfer through a fluid

D) None of the above

Answer: C) Heat transfer through a fluid

What is the heat required to change the phase of a substance called?

A) Sensible heat

B) Latent heat

C) Specific heat

D) None of the above

Which of the following materials has the highest specific heat capacity?

A) Water

B) Aluminum

C) Iron

D) Copper

Which type of heat transfer does not require a medium?

A) Conduction

B) Convection

D) None of the above

What is the difference between temperature and heat?

A) Temperature is a measure of the average kinetic energy of particles, while heat is the total energy of particles.

B) Temperature and heat are the same thing.

C) Temperature is the total energy of particles, while heat is a measure of the average kinetic energy of particles.

D) None of the above.

Answer: A) Temperature is a measure of the average kinetic energy of particles, while heat is the total energy of particles.

Which of the following is not a state function?

A) Enthalpy

B) Temperature

C) Internal energy

D) Entropy

What is the unit of thermal conductivity?

A) W/m²

B) J/kg

C) J/m³

D) W/mK

## Subjective Short Notes Midterm & Finalterm Prepration Past papers included

What is thermal equilibrium?

Ans: Thermal equilibrium is a state where there is no net flow of heat between two systems in contact. The temperature of the two systems becomes equal at this point.

Define specific heat capacity.

Ans: Specific heat capacity is the amount of heat energy required to raise the temperature of one unit mass of a substance by one degree Celsius.

What is the difference between a conductor and an insulator?

Ans: A conductor is a material that allows the transfer of heat easily, while an insulator is a material that does not allow the transfer of heat easily.

What is the difference between conduction and convection?

Ans: Conduction is the transfer of heat energy through a material due to the transfer of kinetic energy from one particle to another. Convection, on the other hand, is the transfer of heat energy due to the movement of fluids or gases.

What is the first law of thermodynamics?

Ans: The first law of thermodynamics states that energy cannot be created or destroyed, only converted from one form to another.

How does the rate of heat transfer vary with distance?

Ans: The rate of heat transfer decreases with distance. This is because the heat energy is dispersed over a larger area as it moves away from the source.

What is the difference between heat and temperature?

Ans: Heat is a form of energy, while temperature is a measure of the average kinetic energy of the particles in a substance.

Define latent heat.

Ans: Latent heat is the amount of heat energy required to change the state of a substance without changing its temperature.

What is thermal expansion?

Ans: Thermal expansion is the tendency of materials to expand when heated and contract when cooled.

What is a thermocouple?

Ans: A thermocouple is a device used to measure temperature by utilizing the voltage generated by the junction of two different metals at different temperatures.

Heat is a form of energy that is transferred between systems or objects that are at different temperatures. It always flows from a hotter object to a colder object. In physics, heat is considered to be a type of energy that is transferred by a mechanism called thermal conduction. Heat transfer occurs in three ways: conduction, convection, and radiation. Conduction occurs when two objects are in direct contact with each other, and heat is transferred through the collision of their molecules. Convection occurs when a fluid, such as air or water, is heated and the hotter portions rise, while the cooler portions sink. Radiation occurs when heat is transferred through electromagnetic waves.

### Thermodynamics:

Thermodynamics is the study of the relationships between heat, work, and energy. It is a branch of physics that deals with the behavior of large groups of particles, such as gases, liquids, and solids. The laws of thermodynamics describe how energy is transferred between systems and how energy is transformed from one form to another. The first law of thermodynamics is the law of conservation of energy. It states that energy cannot be created or destroyed, but it can be converted from one form to another. This law is also known as the law of energy conservation. The second law of thermodynamics states that in any process, the total entropy of the system and its surroundings always increases over time. Entropy is a measure of disorder or randomness in a system. The second law of thermodynamics is also known as the law of entropy. Heat Engines: A heat engine is a device that converts heat energy into mechanical energy. The most common types of heat engines are internal combustion engines and steam engines. These engines work on the principle of the second law of thermodynamics. The efficiency of a heat engine is defined as the ratio of the work done by the engine to the heat input. The efficiency of a heat engine is always less than 100% because some of the heat input is lost to the surroundings. Refrigerators and Heat Pumps: A refrigerator is a device that transfers heat from a colder region to a hotter region. It works on the principle of the second law of thermodynamics, which states that heat flows from hotter regions to colder regions. The refrigeration cycle involves the transfer of heat from the refrigerated space to the external environment. A heat pump is a device that transfers heat from a colder region to a hotter region by using mechanical work. Heat pumps are used in air conditioning systems and in heating systems for homes and buildings. Thermal Conductivity: Thermal conductivity is a measure of a material's ability to conduct heat. Materials with high thermal conductivity conduct heat well, while materials with low thermal conductivity conduct heat poorly. Metals have high thermal conductivity, while insulators such as wood and plastic have low thermal conductivity. The thermal conductivity of a material can be measured using a thermal conductivity meter. This meter measures the rate of heat flow through a material and calculates its thermal conductivity. Conclusion: In conclusion, heat is an important form of energy that is transferred between systems or objects that are at different temperatures. Heat transfer occurs through conduction, convection, and radiation. Thermodynamics is the study of the relationships between heat, work, and energy. Heat engines, refrigerators, and heat pumps are devices that convert heat energy into other forms of energy. Thermal conductivity is a measure of a material's ability to conduct heat. Understanding these concepts is essential for a deeper understanding of thermodynamics and heat transfer.