# Illustration Relationship between voltage and kinetic energy

A positively charged box (plus pole) with the charge $$Q$$ is located at a certain distance from a negatively charged box (minus pole) with the charge $$Q$$. A small test charge $$q$$ is placed near the positive box. This test charge experiences an attractive force in the direction of the negatively charged box. It is accelerated and reaches a certain speed at the negative box. Thus the test charge has gained kinetic energy $$W$$. If you divide this energy by the test charge $$q$$, you get the voltage $$U$$ between the two poles:$U ~=~ \frac{W}{q}$