Q21 of 26 Page 294

Explain why:

heating systems based on circulation of steam are more efficient in warming a building than those based on circulation of hot water

A heating system based on the circulation of steam is more efficient in warming a building than that based on the circulation of hot water. This is because steam contains surplus heat in the form of latent heat (540 cal/g).


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21

Explain why:

a brass tumbler feels much colder than a wooden tray on a chilly day

 21

Explain why:

an optical pyrometer (for measuring high temperatures) calibrated for an ideal black body radiation gives too low a value for the temperature of a red hot iron piece in the open, but gives a correct value for the temperature when the same piece is in the furnace

 21

Explain why:

the earth without its atmosphere would be inhospitably cold

 22

A body cools from 80 °C to 50 °C in 5 minutes. Calculate the time it takes to cool from 60 °C to 30 °C. The temperature of the surroundings is 20 °C.