Who was Gustav Kirchhoff?

German physicist who established the theory of spectrum analysis, contributed to engineering and thermodynamics as well.

Most high school and engineering students know Gustav Kirchhoff by his namesake circuit laws. But there is more to him than that as we shall see. Gustav Kirchhoff was born on 12 March, 1824 in Prussia (now Germany).

Besides circuit laws, Kirchhoff is known for making pioneering contributions to spectroscopy. With scientist Robert Bunsen, he invented the spectroscope in its modern form. He used it to study the spectrum of the Sun.

In 1859, he showed that the Sun contained sodium apart from Hydrogen and Helium. His spectroscopic work earned him greater fame in his native country. Since 1990, a little over 100 years after his death, the Bunsen–Kirchhoff Award has been given for outstanding achievements in spectroscopy.

Now coming back to electricity. You will be amazed to know that Kirchhoff was only a student when he formulated the two circuit laws in 1845. It later became his doctoral dissertation as well. The two laws are as follows:

1. The algebraic sum of currents meeting at a point is zero.
2. The directed sum of the voltages around any closed loop is zero.
They can be used to solve many problems in physics and engineering. Let's have a crack at it with a simple example.

Since (i) the sum of currents at a point must be zero and (ii) currents i1 and i2 are incoming (positive) and i3 and i4 (negative) are outgoing...therefore: 3+9-5-i3=0. This gives i3=7 amp.

That was current law in its simplest form. But combined with voltage law they can be used to solve very complicated circuits.

Apart from spectroscopy and engineering, Kirchhoff made equally important contribution to the field of thermochemistry. In 1858, he gave a law: The overall enthalpy of the reaction will change if the increase in the enthalpy of products and reactants is different.

In 1860, Kirchhoff coined the term black-body radiation and postulated the existence of a perfect black-body, an object that absorbs all the incoming light and reflects none. His studies were used by Max Planck to formulate the Planck's law in 1900.

Although Kirchhoff has become most widely known for his circuit laws but you can realize now how important his other findings were. To the fields of spectroscopy and thermodynamics. Gustav Kirchhoff was a proper genius.