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Electromagnetic Systems - Basic Operations
The Faraday Principle

In 1820 Oersted discovered that a current traveling along a conductor has a magnetic effect on its surroundings. This connection between electricity and magnetism interested scientists of the day and after many failures Michael Faraday made the great discovery of Electromagnetic Induction on August 29 1831, in which he obtained an electric current from a magnetic field.

The main ingredients of the Faraday Principle are shown above in a diagram representing a set-up to illustrate the basic principle. Let's take a coil with a large number of turns, and connect it to a sensitive meter called a galvanometer. If you move the permanent magnet towards the coil the needle on the meter will move in one direction indicating an electric current. Now if the magnet is moved away from the coil the needle deflects in the opposite direction than before. If no motion of the magnet is present, the needle returns to the original position indicating no induced current. The faster the movement, the greater the voltage induced in the coil system.

The exact same Faraday principle is adopted in the probes, the coil is replaced by water (also a conductor), the induced voltage appearing across the two electrodes. As discussed above, the faster the velocity, the greater the induced voltage, easy!