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Ohm’s Law and Definitions of Voltage, Current and Resistance in a Circuit

Georg Simon Ohm, a famous German physicist and mathematician, gave  an important concept about electrical circuits, known as  Ohm’s Law.  According to this law, the current in a circuit is directly proportional to the voltage applied to the circuit and it is  inversely to the resistance.

Relationship between Voltage and Current:

According to this law, the current in electric circuit is directly proportional to supply voltage i.e., if the supply voltage is increased, the current in the circuit will also increase with the same ratio.  Same is the case if the supply voltage is decreased, the current in the circuit will also decrease with the same ratio, but the condition for it is that the resistance of the circuit does not change (or remain constant).

According to Ohm’s law the relationship between current and voltage can be written as:

V \propto I                          …….(1)

Relationship between Current and Resistance:

According to this law, the current in an electric circuit is inversely proportional to the resistance i.e., if the resistance in the circuit is increased, the current in the circuit will decrease and if the resistance in the circuit is decreased, the current in the circuit will increase with the same ratio.

According to Ohm’s law the relationship between current and resistance can be written as:

I \propto \frac{1}{R}                     …….(2)

Joining Equation (1) and (2), we get

I \propto \frac{V}{R} \implies I = K\frac{V}{R}

Here K is the constant, if Voltage, Current and Resistance are taken in unit values, then the value of K is one, So K can be neglected.

Mathematical form of Ohm’s Law:

The  mathematical form of ohm’s law shows the relationship between  Voltage, Current and Resistance as follows:

I = \frac{V}{R}

R = \frac{V}{I}

V=IR

The unit of Voltage is Volt (V), Current is Ampere (A) and Resistance is Ohm (\Omega) . The Ohm’s law can be shown in the form of a triangle as below:

 

ohm's law triangle
Ohm’s law triangle

The above triangle can be used to obtain different forms of Ohm’s Law:

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

Current (I)= \frac {Voltage (V) }{ Resistance(R)}

Resistance(R) = \frac {Voltage (V) }{ Current (I)}

 

 

ohm's law triangle

Ohm’s law can only be considered or applied for DC circuits or pure Resistive AC circuits. It can never be applied for inductive or Capacitive Circuits.

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