BMST Thermodynamics and Heat Transfer — Questions and Answers
Question 1: What is the formula to convert a temperature from Celsius to Fahrenheit?
- °F = (°C × 9/5) + 32 (Correct answer)
- °F = (°C + 32) × 5/9
- °F = °C × 5/9 + 32
- °F = (°C − 32) × 9/5
Correct answer: °F = (°C × 9/5) + 32
The standard conversion is °F = (°C × 9/5) + 32. For example, 100°C = (100 × 1.8) + 32 = 212°F (boiling point of water).
Question 2: What is absolute zero in Celsius?
- −273°C (Correct answer)
- 0°C
- −100°C
- −459°C
Correct answer: −273°C
Absolute zero (0 K) is −273.15°C, commonly rounded to −273°C. At this temperature, all molecular motion theoretically stops.
Question 3: Which method of heat transfer requires no medium and can travel through a vacuum?
- Radiation (Correct answer)
- Conduction
- Convection
- Evaporation
Correct answer: Radiation
Radiation transfers heat via electromagnetic waves (infrared) and requires no medium. This is how the Sun's heat reaches Earth through the vacuum of space.
Question 4: When a substance changes from liquid to gas, what happens to the temperature during the phase change (at constant pressure)?
- It remains constant (Correct answer)
- It increases steadily
- It decreases
- It fluctuates unpredictably
Correct answer: It remains constant
During a phase change, energy input goes into breaking intermolecular bonds rather than raising temperature. Temperature stays constant until the phase change is complete.
Question 5: A metal rod expands when heated. This is an example of:
- Thermal expansion (Correct answer)
- Thermal conductivity
- Specific heat capacity
- Convection
Correct answer: Thermal expansion
Thermal expansion is the tendency of matter to increase in volume when heated. Most solids, liquids, and gases expand as temperature rises due to increased molecular motion.
Question 6: If 500 J of heat is added to 1 kg of water (specific heat = 4,200 J/kg·°C), by approximately how much does the temperature rise?
- 0.12°C (Correct answer)
- 1.2°C
- 12°C
- 0.012°C
Correct answer: 0.12°C
ΔT = Q / (m × c) = 500 / (1 × 4200) ≈ 0.119°C ≈ 0.12°C. Water has a high specific heat, meaning it requires a lot of energy to change temperature.
BMST Thermodynamics and Heat Transfer
What is the formula to convert a temperature from Celsius to Fahrenheit?