Question

In changing the state of thermodynamics from A to B state, the heat required is Q and the work done by the system is W. The change in its internal energy is
A $Q + W$
B $Q - W$
C $Q$
D $\dfrac{{Q - W}}{2}$

Answer 1

Hint: This question is based on thermodynamics. Thermodynamics is the study of heat and energy. It describes how the energy is converted into another form. The thermodynamics first law gives the relation between the internal energy, heat and work.

Complete step by step answer:
We know that the first law of thermodynamic states that the energy can be converted into one to another form, but it cannot be created or destroyed under any condition. With the interaction of heat, work and internal energy, the energy is converted into another form.

The numerical form of the first law of thermodynamics is given as,
$\Delta U = Q - W$
Here \[\Delta U\] is the change in internal energy, \[Q\] is the heat exchanged between a system and its surrounding and $W$ is the work done by or on the system.
There are various engines and devices working on the principle of first law of thermodynamics. We use the sign convention to get proper expression for the internal energy. Heat engine is a good example of this law.
The following sign conventions, if \[Q\] is positive, then there is a net heat transfer into the system; if W is positive, then there is net work done by the system. So positive \[Q\] adds energy to the system and positive.

So, the correct answer is “Option B”.

Note:
In this question, students must have knowledge of thermodynamics and the first law of thermodynamics. The sign is the important part of the expression of the first law. If work done by the system is positive then the work is done by the system.