To which of the following does the first law of thermodynamics apply?

A. heating objects

B. transferring thermal energy

C. doing work on a system

D. all of the above

The best answer is D.

All the above are correct because they involve transfer or change of energy from one form to another.

The first law of thermodynamics states that energy can't be created or destroyed, but it can be changed. Anything that uses energy is simply changing the energy from one kind of energy to another. It cannot be created and also never goes away.

Change in energy can be used by people to do useful work. There are different forms of energy such as heat, light, electricity and mechanical energy. Today electrical energy has been changed to light energy in electrical bulbs and heat energy in electric cookers or hot plates in our kitchens.