Physics – Short Questions

Heat and Thermodynamics

According to HSEB Exam format for Physics (XI), three short questions each of 2 marks are asked from Heat and Thermodynamics where any two  must be answered. But there are many more questions to be prepared for, from various topics. Here are the selected short questions from the overall chapters of Heat and Thermodynamics which will not only save your exam preparation time but also help you score better marks.

  1. Why does heat flow from a body at higher temperature to a body at lower temperature?
  2. A thermometer is laid out in direct sunlight. Does it measure the temperature of the air, of the sun or what?
  3. What is the temperature of a vacuum?
  4. Does the coefficient of linear expansion depend on length? Explain.
  5. Under what condition, the difference in length of the two rods remains the same at all temperature?
  6. A clock which has a brass pendulum beats correctly at 30˚C. Will it run faster or slower if the temperature (a) decreases and (b) increases?
  7. Two bodies made of the same material have the same external dimensions and appearance but one is solid and the other is hollow. When they are heated is the overall volume expansion the same or different?
  8. When a metallic block with hole in it is heated, why does not the material around the hole expand into the hole and make it smaller?
  9. Why are telephone wires taut in winter and slag in summer?
  10. The specific heat capacity of water is quite high. Explain why this fact makes water particularly good for a heating system?
  11. Why do animals eat more in winter than in summer?
  12. During high fever, a wet cloth is kept on the forehead of a person. Why?
  13. A student claimed that when two bodies not initially in thermal equilibrium are placed in contact, the temperature rise of the cooler body must always equal the temperature drop of the warmer. Do you agree? Is there a principle of conservation of temperature or something like that?
  14. Why do you think the heat of vaporization is so much larger than the heat of fusion?
  15. Why does food cook faster in a pressure cooker than in an open pot?
  16. A student asserts that a suitable unit for specific heat capacity is m2/s2˚C. Is it correct?
  17. Explain why two pieces of ice stick when compressed together?
  18. How does the melting and boiling point of a substance vary with pressure?
  19. In deriving Boyle’s and Charle’s laws, we assume ideal gas. What will happen if we do not assume ideal gas situation?
  20. When a car is driven some distance, the air pressure in the tyre increases. Why?
  21. As you go high in the earth’s atmosphere, the ratio of N2 to O2 molecules increases. Why?
  22. The size of different molecules does not enter into the gas laws. Why?
  23. Will the temperature of a gas in a container increase when we put the container in a moving train? Explain.
  24. Absolute zero temperature is not zero energy temperature. Explain.
  25. The pressure of a gas increases with increase of temperature. Explain on the basis of kinetic theory.
  26. Molecules of different gases have equal average kinetic energies provided their temperature is the same. Do these molecules have equal velocities also?
  27. Distinguish between saturated and unsaturated vapour pressure.
  28. Explain why are dews formed in a clear night but not in the cloudy night?
  29. Show that there exists a single value of triple point of a substance.
  30. Why are you more uncomfortable on a hot day when the humidity is high than when it is low?
  31. Why it takes longer time to dry wet clothes in rainy summer than in sunny winter?
  32. Why is the triple point of water chosen as a standard fixed point in modern thermometry?
  33. Explain the difference between dew point and critical point.
  34. Why are two thin blankets warmer than a single blanket of double the thickness?
  35. On hot sunny days, a house can be kept cooler if the windows are closed and the curtain pulled to cover the windows. Explain.
  36. Why are mud-houses colder in summer and warmer in winter?
  37. Cooking utensils are blackened at the bottom and polished on the upper surface. Why?
  38. Ventilations are provided near the ceilings in a room. Explain this statement.
  39. What would be the temperature of the earth if the atmosphere were not present?
  40. A certain quantity of ideal gas is compressed to half of its initial volume. The process may be adiabatic or isothermal. For which process greater amount of mechanical work is required.
  41. Air escaping from an air-hose at a gas station always feels cold. Why?
  42. Explain why temperature of gas drops in an adiabatic expansion.
  43. A thermos bottle contains coffee. The thermos bottle is vigorously shaken. Consider the coffee as the system.(a) Does its temperature rise or fall? (b) Has heat been added to it? (c) Has work been done on it? (d) Has its internal energy changed?
  44. Why has a gas two values of molar heat capacities?
  45. Why is Cp greater than Cv?
  46. Can a room be cooled by leaving the doors of an electric refrigerator open in a closed room?
  47. Why an engine cannot achieve 100% efficiency?
  48. Why is a petrol engine called a four stroke engine?
  49. Petrol engine is less efficient than diesel engine. Explain why?
  50. Why do diesel engines need no spark plugs whereas petrol engines need them?

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