Question

Which of the following laws of thermodynamics defines internal energy?

• A. Zeroth law
• B. Second law
• C. First law
• D. None of the above

Answer 1

The correct option is C First law

Internal energy is the sum of all the energies of a molecule in the frame of reference of the system.
According to $I^{st}$ law,
$\Delta Q=\Delta U+\Delta W$
where $\Delta U$ is internal energy, $\Delta W$ is the work done and $\Delta Q$ is the heat transferred.

$\Delta U=\Delta Q-\Delta W$
Thus, option (c) is the correct answer.