Why is the efficiency of a machine always less than 100 percent?

Because of friction.

Explanation:

Efficiency is always less than 100% because there is always energy loss in each and every process. This loss is in the form of friction. Also, since friction is the core reason that the mechanical world exist. We even can't walk on the road if the friction is not present. Hence, we can't deny from the fact that

it also reduces the efficiency from 100%.

when cloud cover increases then the suns ray's which provides the earth with light and warmth gets covered due to the due to the suns ray's being blocked, the temperature in that region

therefore to conclude i would like to say that,

=more the cloud cover, the lesser the

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