**Work - energy transferred between systems**

The amount of energy that is transferred between so-called ‘physical systems’ is called work. We can speak about it in the context of mechanical processes (we speak about work in progress and rotation), thermodynamic processes (generalised and volumetric work) and electric current. If we speak of work as moving a body a certain distance using a force, then work is expressed as the product of that force and distance. This formula for work is the most straightforward. The unit of work is the joule, denoted by the symbol J.

**Work in mechanical processes**

A more complicated version of the work formula is one where we consider work to be the scalar product of an applied force vector and a displacement vector. Only if the vectors are arranged in parallel can the work formula be simplified to the previous one. However, if the cosine of the angle between the vectors is not equal to 1, we must take then this fact into account in our calculations. After that, we multiply the value of the force used, the displacement and the cosine of the angle mentioned above. If the force used has changed, then its value on the way should be averaged. Quite

**Work in the case of an electric current**

If we are talking about an electric current, then the formula for work presents itself differently. The electric charge is multiplied by the voltage or potential difference – this formula determines how much work a 1,000-watt electric device will do in one hour. In the case of electricity, the formula for work comes from the definition of work – i.e., the change in potential energy within a conductor, the transfer of electric charge between points that have a different electric potential from each other.

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