Ohm's Law
Ohm's law defines a linear relationship between the voltage and the current in an electrical circuit.
The DC current flow through a resistor is set by the resistor's voltage drop and the resistor's resistance.
With water flow analogy we can imagine the electric current as water current through pipe, the resistor as a thin pipe that limits the water flow, the voltage as height difference of the water that enables the water flow.


Ohm's Law Formula / Equation
When we know the voltage and resistance, we can calculate the current.
Ohm's law definition
The resistor's current I in amps (A) is equal to the resistor's voltage V R =V in volts (V) divided by the resistance R in ohms (Ω):

V is the voltage drop of the resistor, measured in Volts (V). Sometimes E is used instead of V . E denotes electromotive force. I is the electrical current flowing through the resistor, measured in Amperes (A) R is the resistance of the resistor, measured in Ohms (Ω)
Voltage calculation
When we know the current and resistance, we can calculate the voltage. The voltage V in volts (V) is equal to the to the current I in amps (A) times the resistance R in ohms (Ω):


Resistance calculation
When we know the voltage and the current, we can calculate the resistance. The resistance R in ohms (Ω) is equal to the voltage V in volts (V) divided by the current I in amps (A):V is the voltage drop of the resistor, measured in Volts (V). Sometimes E is used instead of V . E denotes electromotive force. I is the electrical current flowing through the resistor, measured in Amperes (A) R is the resistance of the resistor, measured in Ohms (Ω


Since the current is set by the values of the voltage and resistance, the Ohm's law formula can show that:

• If we increase the voltage, the current will increase.
• If we increase the resistance, the current will reduce.

Example #1
Find the current of an electrical circuit that has resistance of 50 Ohms and voltage supply of 5 Volts.
Solution:
V = 5V
R = 50Ω
I = V / R = 5V / 50Ω = 0.1A = 100mA
Example #2
Find the resistance of an electrical circuit that has voltage supply of 10 Volts and current of 5mA.
Solution:
>V = 10V
I = 5mA = 0.005A
R = V / I = 10V / 0.005A = 2000Ω = 2kΩ

Ohm's Law for AC Circuit
The load's current I in amps (A) is equal to the load's voltage VZ=V in volts (V) divided by the impedance Z in ohms (Ω):
I = V / Z
V is the voltage drop on the load, measured in Volts (V)
I is the electrical current, measured in Amps (A)
Z is the impedance of the load, measured in Ohms (Ω)

Example #3

Find the current of an AC circuit, that has voltage supply of 110V∟70° and load of 0.5kΩ∟20°.
Solution:
V = 110V∟70°
Z = 0.5kΩ∟20° = 500Ω∟20°
I = V / Z = 110V∟70° / 500Ω∟20° = (110V / 500Ω) ∟ (70°-20°) = 0.22A ∟50°

See also

Kirchhoff's laws

Voltage divider rule