In 1834 he began to study electric motors. He moved to St. Petersburg in 1837 to teach at the Academy of Sciences. While studying the transfer of power from a battery to an electric motor, he deduced the following law:
"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."
This law is known as the maximum power theorem or Jacobi's Law.
He also worked on the development of the electric telegraph.