When 20 cal of heat is supplied to a system, the increase in inte… - Vidyadip

MCQ

When $20\ \text{cal}$ of heat is supplied to a system, the increase in internal energy is $50J$. If the external work done is $35J$, the mechanical equivalent of heat is:

✓
$4.25\ \text{J/ cal}$
B
$1.26\ \text{J/ cal}$
C
$4.92\ \text{J/ cal}$
D
$2.1\ \text{J/ cal}$

✓

Answer

Correct option: A.

$4.25\ \text{J/ cal}$

According to first law of thermodynamics $\text{J}\triangle\text{Q}=\triangle\text{W}+\triangle\text{U},$
where $J$ is the mechanical equivalent of heat.
$J \times 20 = 50 + 35$
$J = 4.25\ \text{J/ cal}$

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