Ohm's Law states that the current flowing through a circuit is equal to the voltage across the circuit divided by its resistance.
What Is Ohm's Law?
Ohm's Law is a fundamental principle used in electrical and electronic engineering to describe the relationship between voltage, current and resistance.
When the resistance of a circuit is known, Ohm's Law can be used to calculate the current for a given voltage. Similarly, it can be used to determine voltage or resistance when the other two quantities are known.
The three electrical quantities are:
- Voltage (V) — electrical potential difference
- Current (I) — flow of electric charge
- Resistance (R) — opposition to current flow
Ohm's Law Formula
The standard form of Ohm's Law is:
Where:
| Symbol | Quantity | Unit |
|---|---|---|
| V | Voltage | Volt (V) |
| I | Current | Ampere (A) |
| R | Resistance | Ohm (Ω) |
Ohm's Law Triangle
The formula can be rearranged to calculate any of the three quantities.
Worked Example
Suppose a 24 V DC supply is connected to a resistor with a resistance of 12 Ω. What current will flow through the resistor?
Step 1 — Identify the values
V = 24 V
R = 12 Ω
Step 2 — Apply Ohm's Law
Step 3 — Calculate
Therefore, the current flowing through the resistor is 2 amperes.
Engineering Notes
Ohm's Law is frequently used as a starting point for electrical calculations, but real electrical systems can be more complex.
For example, motors, transformers and many electronic components do not always behave as simple constant-resistance loads.
In practical electrical engineering, Ohm's Law is often combined with other relationships such as electrical power:
Combining these equations allows engineers to calculate power, current and resistance in many electrical circuits.
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What is the basic formula of Ohm's Law?
The basic formula is V = I × R, where V is voltage, I is current and R is resistance.
What happens when resistance increases?
If voltage remains constant, increasing resistance reduces the current according to I = V ÷ R.
Is Ohm's Law applicable to AC circuits?
Ohm's Law applies directly to resistive components. AC circuits containing inductance or capacitance require impedance-based calculations.