In the first law of thermodynamics, heat supplied = increase in internal energy + __________.

In the first law of thermodynamics, the equation typically formulated is: heat supplied (Q) = increase in internal energy (ΔU) + work done (W). This law reflects the principle of conservation of energy, stating that the energy supplied to a system as heat can either increase the system's internal energy or be converted into work done by the system.

The concept of work done in this context refers to the energy transferred when the system performs mechanical work, such as moving a piston in a cylinder. In essence, when energy is added to a system as heat, part of it may increase the internal energy (which results in a temperature change, for example), and the remaining part may be utilized to do work on the surroundings.

The inclusion of "work done" in the equation highlights the dual nature of energy transfer: it can enhance the internal state of the system or be converted into mechanical energy that does work. This understanding is significant in analyzing energy transformations in thermodynamic processes, making it essential knowledge for power engineers.