An ideal heat engine operates of fixed difference of temperatures between hot and cold reservoirs, say 100k. what will provide greater efficiency: operation with the hot reservoir as hot as possible, or operation with a cold reservoir as cold as possible?

To solve this problem we will apply the concepts given for the efficiency of an engine which is given as

Where

= Temperature of the cold reservoir

= Temperature of the hot reservoir

The efficiency maximum would be given only if

Replacing this value we have

Therefore: Cold reservoir as cold as possible provide the greater efficiency.

blue light is scattered in different directions by the tiny molecules of air. blue is scattered more than other colours because it has a shorter distance to travel which results in smaller waves. this is why we see a blue sky most of the time.