Multiple Choice Questions
Physics: Thermodynamics and Energy Transfer
Topic: Thermodynamics and Energy Transfer
Grade: 11
Question 1:
Which of the following statements best describes the first law of thermodynamics?
A) Energy can neither be created nor destroyed, only transferred or transformed.
B) The entropy of a system tends to increase over time.
C) The pressure and volume of a gas are inversely proportional at constant temperature.
D) The efficiency of a heat engine is always less than 100%.
Answer: A) Energy can neither be created nor destroyed, only transferred or transformed.
Explanation: The first law of thermodynamics, also known as the law of conservation of energy, states that energy can neither be created nor destroyed, only transferred or transformed from one form to another. This means that the total energy of a closed system remains constant. For example, when a ball is dropped from a height, its potential energy is converted into kinetic energy as it falls.
Example 1: When a cup of hot coffee is left on a table, the heat energy from the coffee is gradually transferred to the surroundings, resulting in a decrease in the coffee\’s temperature.
Example 2: In a car engine, the chemical energy from the combustion of fuel is converted into mechanical energy to propel the car forward.
Question 2:
Which of the following processes is an example of an adiabatic process?
A) Boiling water in a pot.
B) Melting ice into water.
C) Compressing a gas in a cylinder with no heat transfer.
D) Heating a metal rod with a flame.
Answer: C) Compressing a gas in a cylinder with no heat transfer.
Explanation: An adiabatic process is a thermodynamic process in which no heat is transferred to or from the system. In this case, compressing a gas in a cylinder without any heat transfer is an example of an adiabatic process. This can be achieved by insulating the cylinder to prevent any heat exchange. As the gas is compressed, its temperature and pressure increase, while its volume decreases.
Example 1: When a bicycle pump is used to inflate a tire, the compression of air inside the tire is an adiabatic process since there is no heat transfer between the system (air) and its surroundings.
Example 2: The compression stroke in an internal combustion engine is an adiabatic process, as the fuel-air mixture is compressed by the piston without any heat transfer. This leads to an increase in temperature and pressure, which ultimately results in the combustion of the mixture.