Q.1. What do you mean by triple point ?
AnswerAnswer: It is a particular point in the phase diagram, representing a particular pressure and temperature at which a substance can coexist in all three phases in solid, liquid and gas.
Q.2. Why the triple point of water is considered as a standard fixed point in thermometry?
AnswerAnswer: Triple point of water is fixed and occurs only for particular values of pressure = 0.46 cm of Hg and temperature = –273.16 K.
Q.3. What is the specific heat of a gas in an isothermal process?
Q.4. What is the specific heat of gas in an adiabatic process?
AnswerAnswer: For adiabatic process, Q = 0 ⇒ C = 0.
Q.5. Two rods A and B are of equal lengths. Each rod has the ends at temperatures T1 and T2. What is the condition that will ensure equal rates of flow of heat through the rods A and B?
Q.6. What is the thermal conductivity of a perfect heat conductor and a perfect heat insulator?
AnswerAnswer: For perfect heat conductor, thermal conductivity is infinity whereas for perfect insulators, thermal conductivity is zero.
Q.7. The temperature of a black body is increased from 200 K to 400 K. How will the ratio of emission of energy change?
AnswerAnswer: By Stefan’s law, E α T^4 Here, temperature becomes double. Therefore, E will increase 2^4 or 16 times.
Q.8. Three stars appear as green, red and blue in colour. Which has maximum temperature?
Q.9. Why a clinical thermometer should not be sterilized by boiling?
AnswerAnswer: The range of clinical thermometer is usually from 95° F to 110° F and the boiling point of water is 212°F. So on sterilization by boiling, the capillary of thermometer will burst due to thermal expansion of mercury in the capillary.
Q.10. Explain why a beaker filled with water at 4°C overflows if the temperature is decreased or increased?
AnswerAnswer: It is because of the anomalous expansion of water. Water has a maximum density at 4°C. Therefore, water expands whether it is heated above 4°C or cooled below 4°C.
Q.11. Two identical rectangular strips of copper, and the other of steel are riveted to form a bimetallic strip. What will happen on heating?
AnswerAnswer: Since α for copper is more than α for steel, hence on heating, the bi-metallic strip will bend in such a way that the copper strip remains on outer or convex side.
Q.12. Why must telephone or power lines necessarily sag a little?
AnswerAnswer: The sag is allowed for contraction in winter. If no sag is allowed, the wire may snap in extremely cold weather.
Q.13. Which object will cool faster when kept in open air, the one at 300°C or the one at 100°C Why?
AnswerAnswer: The object at 300°C will cool faster than the object at 100°C. This is in accordance with Newton’s law of cooling, Rate cooling of an object α Temperature between the object and its surroundings
Q.14. Why a body with large reflectivity is a poor emitter?
AnswerAnswer: A body whose reflectivity is large would naturally absorb less heat. So, a body with large reflectivity is a poor emitter.
Q.15. Can the temperature of a body be negative on the Kelvin scale?
AnswerAnswer: No. This is because the absolute zero on the Kelvin scale is the minimum possible temperature.
Q.16. The earth without its atmosphere would be inhospitably cold. Explain.
AnswerAnswer: The atmosphere serves purpose of a blanket over the earth and it does not allow earth’s heat to be radiated during night.
Q.17. Heating systems based on circulation of steam are more efficient in warming a building than those based on circulation of hot water.