NSAA NSAA Physics - Thermal Physics and Thermodynamics 1 — Questions and Answers
Question 1: What is the SI unit of temperature used in thermodynamic equations?
- Celsius (°C)
- Kelvin (K) (Correct answer)
- Fahrenheit (°F)
- Rankine (°R)
Correct answer: Kelvin (K)
The Kelvin is the SI unit of thermodynamic temperature, defined so that absolute zero is 0 K.
Question 2: The zeroth law of thermodynamics states that if object A is in thermal equilibrium with object B, and B is in thermal equilibrium with object C, then:
- A has more thermal energy than C
- A and C are in thermal equilibrium with each other (Correct answer)
- B must be hotter than both A and C
- A and C may or may not be at the same temperature
Correct answer: A and C are in thermal equilibrium with each other
The zeroth law establishes that thermal equilibrium is transitive — objects sharing a common thermal equilibrium temperature are in equilibrium with each other.
Question 3: For an ideal gas, the internal energy depends only on:
- Pressure alone
- Volume alone
- Temperature alone (Correct answer)
- Both pressure and volume
Correct answer: Temperature alone
For an ideal gas, intermolecular forces are neglected, so internal energy is purely kinetic and depends only on temperature.
Question 4: Which law of thermodynamics is the law of conservation of energy?
- Zeroth Law
- First Law (Correct answer)
- Second Law
- Third Law
Correct answer: First Law
The first law states that the change in internal energy equals heat added to the system minus work done by the system (ΔU = Q − W), embodying energy conservation.
Question 5: The specific heat capacity of water is 4,200 J kg⁻¹ K⁻¹. How much energy is required to raise 2 kg of water by 5°C?
- 840 J
- 4,200 J
- 21,000 J
- 42,000 J (Correct answer)
Correct answer: 42,000 J
Using Q = mcΔT = 2 × 4,200 × 5 = 42,000 J.
Question 6: During an isothermal process involving an ideal gas, which quantity remains constant?
- Pressure
- Volume
- Temperature (Correct answer)
- Entropy
Correct answer: Temperature
An isothermal process occurs at constant temperature; for an ideal gas this also means constant internal energy.
Question 7: The relationship between the Kelvin and Celsius scales is:
- K = °C + 100
- K = °C − 273
- K = °C + 273 (Correct answer)
- K = °C × 1.8
Correct answer: K = °C + 273
The Kelvin scale is offset from Celsius by 273.15, so K = °C + 273 (to three significant figures).
NSAA NSAA Physics - Thermal Physics and Thermodynamics 1
What is the SI unit of temperature used in thermodynamic equations?