Question

A Carnot engine working between $300\, K$ and $400\, K$ has $800\, J$ of useful work. The amount of heat energy supplied to the engine from the source is

• A. 2400 J
• B. 3200 J
• C. 1200 J
• D. 3600 J

Answer 1

Answer: (B)

3200 J

Answer 2

$\eta =\frac{\text { Work done }}{\text { Heat supplied }}$
$=\frac{T_{1}-T_{2}}{T_{1}}=\frac{W}{Q_{1}}$
$W =800\, J , T_{1}=400\, K , T_{2}=300 \,K$
On substitution the values
$\frac{800}{Q_{1}} =\frac{400-300}{400}$
$=\frac{100}{400}=\frac{1}{4}$
$Q_{1} =800 \times 4=3200\, J$