Let's address each question in sequence, explaining the concepts and solutions step by step.
Question 5: For an isothermal process, which of the following statements is correct?
To answer this, we need to understand an isothermal process. In thermodynamics, an isothermal process is a change that occurs at a constant temperature. For an ideal gas undergoing an isothermal process, the internal energy remains constant because internal energy is solely a function of temperature.
- A. Work, heat, and internal energy all undergo changes.
This is incorrect because the internal energy does not change in an isothermal process.
- B. Work and heat balance each other, so that there is no change in internal energy.
This is correct. In an isothermal process, any heat added to the system (Q) is used to do work (W), maintaining constant internal energy (ΔU = 0).
- C. No energy is transferred as heat; internal energy change is due to work.
This is incorrect because heat transfer does occur in an isothermal process.
- D. No work is done; internal energy change is due to heat.
This is incorrect because work is done in an isothermal process.
Answer: B
Question 6: Which concept does the first law of thermodynamics describe?
The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or transformed. It is essentially the law of conservation of energy.
- A. Conservation of mass
This is incorrect. Conservation of mass is a different principle.
- B. Conservation of energy
This is correct. The first law of thermodynamics describes the conservation of energy.
- C. Conservation momentum
This is incorrect. Momentum conservation is governed by its own principle.
- D. Conservation of angular momentum
This is incorrect. Angular momentum conservation is another distinct principle.
Answer: B
Question 7: A steam engine takes in 2750 J of energy as heat, and does 850 J of work. Using the given equations, find the change in internal energy of the steam engine.
To find the change in internal energy (ΔU), we use the first law of thermodynamics, which is given by:
[tex]\[ \Delta U = Q - W \][/tex]
Where:
- [tex]\( Q \)[/tex] is the heat added to the system (2750 J)
- [tex]\( W \)[/tex] is the work done by the system (850 J)
Substituting the values:
[tex]\[ \Delta U = 2750 \text{ J} - 850 \text{ J} = 1900 \text{ J} \][/tex]
Answer: B
Question 8: Which of the following statements about an ideal cyclic process is correct?
In an ideal cyclic process, the system returns to its initial state at the end of the cycle. This means the internal energy change over one complete cycle is zero (ΔU = 0). Any energy added as heat (Q) is completely converted into work (W) during the cycle.
Therefore, the correct statement is:
- The energy added as heat is converted entirely to work.
This implies that in an ideal cyclic process, there is no net change in internal energy, and all the heat energy input is used to perform work.
Answer: The energy added as heat is converted entirely to work.
