1.

A Carnot engine whose sink is at 300 K has an efficiency of 40 %. By how much should the temperature of source be increased so as to increase its efficiency by 50% of original efficiency?

Answer»

`380 K`
`275 K`
`325 K`
`250 K`

Solution :Efficiency of a Carnot engine, `eta = 1 - T_(2)/T_(1)`
or, `T_(2)/T_(1) = 1 - eta = 1 - 40/100 = 3/5`
` :. T_(1) = 5/3 xx T_(2) = 5/3 xx 300 = 500 K`.
Increase in efficiency = `50% " of " 40% = 20%`
New efficiency, `eta. = 40% + 20% = 60%`
` :. T_(2)/T_(1) = 1 - 60/100 = 2/5`
` rArr T_(1). = 5/2 xx T_(2) = 5/2 xx 300 = 750 K`
` :. ` Increse in temperature of SOURCE ` = T_(1). - T_(1)`
` = 750 - 500 = 250 K`


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