GEORG SIMON OHM (1789-1854)

1827 – Germany

‘The electric current in a conductor is proportional to the potential difference’

In equation form, V = IR, where V is the potential difference, I is the current and R is a constant called resistance.

greek symbol capital ohm (480 x 480)

Ohm’s law links voltage (potential difference) with current and resistance and the scientists VOLTA, AMPERE and OHM.

Ohm is now honoured by having the unit of electrical resistance named after him.
If we use units of VI and R, Ohm’s law can be written in units as:

volts = ampere × ohm

photograph of george simon ohm © + diagram of simple electric circuit

GEORG OHM


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GUSTAV KIRCHHOFF (1824- 87)

1845 – Germany

‘First law (Junction law): At any junction point in an electrical circuit, the sum of all currents entering the junction must equal the sum of all currents leaving the junction’

‘Second law (Loop law): For any closed loop in an electrical circuit, the sum of the voltages must add up to zero’

In equation form the first law is I = I1 + I2 + I3 + I4 +…. where I is the total current and I1, I2, I3 etc. are the separate currents.

Second law is V = V1 + V2 + V3 + … where V is the total voltage and V1, V2, V3 etc. are the separate voltages.

photo portrait of GUSTAV KIRCHHOFF ©

GUSTAV KIRCHHOFF

These laws are an extension of OHM‘s law and are used for calculating current and voltage in a network of circuits. Kirchhoff formulated these laws when he was a student at the University of Konisburg.

Kirchhoff also showed that objects that are good emitters of heat are also good absorbers. This is Kirchhoff’s law of radiation.

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