Ohm's Law

Ohm's Law, a principle discovered in 1827 and named after the German scientist, Georg Simon Ohm, is a basic law of electricity. This law defines the mathematical relationship between three fundamental electrical factors; voltage, resistance and electric current. Ohm's law can be applied to electrical circuits and is valid for both direct as well as alternating current.

What exactly is Ohm's Law?

Consider an electric circuit through which an electric current (I) is passed. According to Ohm's Law, the current flowing through the circuit is directly proportional to the potential difference (V) between two points in the circuit and is inversely proportional to the resistance (R) between them.

Experimentally, it is observed that when the voltage between the points is doubled, then the current is also doubled, and if the resistance is doubled, then the current halves, which indicates that the current flowing is directly proportional to the potential difference and is inversely proportional to the resistance.

Parameters involved in Ohm's Law

The different parameters involved in Ohm's Law are voltage, current, resistance and power.

• Voltage (V/E) is the potential difference between two points in a circuit and is measured in volts (V).
• Current (I) is the flow of electric charge from negative to positive on the conductor surface and is measured in amperes (A) or amps.
• Resistance (R) is the measure of opposition caused to the flow of electric current. Resistance determines how much current will actually flow through the conductor and is used to control the levels of current and voltage. Resistance is measured in ohms (Ω).

Ohm's Law's Mathematical Equation

Ohm's Law's Mathematical Equation is the simplest and most important equation that can be used while designing or analyzing circuits. According to Ohm's Law;

Current (I) = Voltage (V) / Resistance (R)

Using this simple mathematical equation, one could use the two known parameters to find the third unknown parameter. For example, if the current flowing and voltage is known, then the resistance can be easily found by reorganizing the above equation.

Resistance (R) = Voltage (V) / Current (I)

If the current and resistance is known, then again by rearranging the formula, the voltage between the two points can be determined.

Voltage (V) = Current (I) × Resistance (R)

The above equations can be used to calculate the current through resistors, voltage drops across resistors, output power and power ratings of resistors.

Another useful equation is that of the power equation, where the power is equal to the voltage multiplied by the current. P = V × I

In case the voltage details are unknown, and only the current and resistance figures are available, we can reorganize the equation and calculate the power directly;

Since V = IR, by substituting this in the above power equation P = VI, we get P = I × R × I

Some of the other equations that can be derived from the standard Ohm's Law equation and the power equation are as follows;

E = IR (Since E, electromotive force = potential difference, V)
R = E/I
I = E/R
P = EI
E = P/I
I = P/E.
P = I2R
R = P/I2
I = sqrt (P/R)
P = E2/R
R = E2/P
E = sqrt (PR)

In Ohm's Law, the voltage and resistance are not affected by changes in the other parameters. Only the current parameter changes according to respective changes in the voltage and resistance. Ohm's Law is extremely useful in the engineering (electrical/ electronic) field, because of the way it relates the three electrical quantities; current, voltage and resistance. It shows how these three are interdependent on a macroscopic level. These equations are used a lot in cases of car audios to find out the current moving through the circuit.