Which one of the following identifies the sources of an electromotive force? Atomic, magnetic, thermal Chemical, atomic, thermal Chemical, magnetic thermal Chemical, magnetic, atomic

## Step 1:Understanding the meaning of Electromotive force (emf). In general physics context, electromotive force (also known as emf) refers to the energy expended to move a unit of positive charge from one point to another against an electric field. ## Step 2:Identifying different sources of emf. Here are the three primary sources:### : This involves the conversion of chemical energy to electrical energy, primarily observed in certain reactions. An example for its source is a battery, which has chemical energy being converted into electrical energy cavusing electron movement (via redox reactions) and lead to creation of voltage difference. ### : This is also known as the Seebeck effect, essentially referring to emf generated due to the difference in temperature between two different metals. Thermocouples for instance, utilize this kind of emf in industries for temperature measurements. ### : The most commonly known form of such emf generation is provided by 'Alternators' or 'Generators', which are devices that convert mechanical power into AC electrical power. Basically, they operate on the principle of ‘Electromagnetic Induction’ – where with rapidly varying magnetic fields, an emf gets induced in a loop of wire.## Step 3:Now we have recognized the primary sources of emf. Coming back to the options, only "Chemical, magnetic, thermal" corresponds to the trio outlined above. Hence, this option is the correct answer.