Q21 of 26 Page 294

Explain why:

the earth without its atmosphere would be inhospitably cold

In the absence of atmospheric gases, no extra heat will be trapped. All the heat would be radiated back from earth’s surface. So, without its atmosphere, earth would be inhospitably cold.


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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

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Explain why:

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

 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.