Moritz Hermann von Jacobi (September 21, 1801 - March 10, 1874) was a Prussian engineer and physicist born in Potsdam. Jacobi worked mainly in Russia. He furthered progress in galvanoplastics , electric motors, and wire telegraphy.

Motors

In 1834 he began to study magnetic motors. He moved to St. Petersburg in 1837 to teach at the Academy of Sciences. He investigated the power of an electromagnet in motors and generators. While studying the transfer of power from a battery to an electric motor, he deduced the maximum power theorem. Jacobi tested motors output by determining the amount of zinc consumed by the battery. With financial assistance of Czar Nicholas, Jacobi constructed in 1839 a 28 foot electric motor boat powered by battery cells. The boat carried 14 passengers. The boat travelled at the speed of three miles per hour.

Jacobi's Law

Circuit Diagram

Power is being transferred from the source,
with voltage V and resistance R_S,
to a load with resistance R_L,
resulting in a current I. I is simply
the source voltage divided by the total

circuit resistance

The law known as the maximum power theorem states:

"Maximum power is transferred when the internal resistance of the source equals the resistance of the load, when the external resistance can be varied, and the internal resistance is constant."

The transfer of maximum power from a source with a fixed internal resistance to a load, the resistance of the load must be the same as that of the source. This law is of use when driving a load such as an electric motor from a battery. Jacobi obtained his theorem by common sense.

Electrotyping and telegraphy

In 1838, he discovered galvanoplastics, or electrotyping, a method of making printing plates by electroplating. The way in which this works is analogous to a battery acting in reverse. The stereotype was an impression taken from a form of movable lead type and used for printing instead of the original type. This technique is used in relief printing .

He also worked on the development of the electric telegraph. In electronics there is often a requirement to match the source (e.g. transmitter) impedance to the load (e.g. antenna) impedance, but this is to avoid reflections in the transmission line. The maximum power theorem is only a part of the reason for this requirement.

External links

• Katz, Eugenii, "Moritz Hermann Jacobi". Biosensors & Bioelectronics.
• Calvert, J. B., "Jacobi's Theorem Also known as the Maximum Power Transfer Theorem, misunderstanding of it retarded development of dynamos". March 30, 2001