What is Ohm’s Law?
Ohm’s Law is one of the most fundamental laws in electrical engineering. It describes the relationship between voltage (V), current (I), and resistance (R) in an electrical circuit.
The law states:
“At constant temperature, the current flowing through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance.”
This law was proposed by the German physicist Georg Simon Ohm in 1827 and forms the foundation of electrical circuit analysis.
Ohm’s Law Formula
The relationship between voltage, current, and resistance is:
V = I × R
Where:
- V = Voltage (Volts, V)
- I = Current (Amperes, A)
- R = Resistance (Ohms, Ω)
Using this equation, we can also calculate:
- Current: I = V / R
- Resistance: R = V / I
Understanding the Formula
Explanation in Simple Words
Imagine water flowing through a pipe.
- Voltage is like the water pressure.
- Current is like the amount of water flowing.
- Resistance is like a narrow section of the pipe that restricts water flow.
If the pressure increases, more water flows.
If the pipe becomes narrower (higher resistance), less water flows.
Electric current behaves in a similar way.
Mathematical Expression
According to Ohm’s Law:
- Current increases when voltage increases.
- Current decreases when resistance increases.
Therefore:
- High Voltage → High Current
- High Resistance → Low Current
SI Units
| Quantity | Symbol | SI Unit |
|---|---|---|
| Voltage | V | Volt (V) |
| Current | I | Ampere (A) |
| Resistance | R | Ohm (Ω) |
Example 1
A resistor of 10 Ω is connected to a 20 V battery.
Given:
Voltage = 20 V
Resistance = 10 Ω
Current = V / R
Current = 20 / 10 = 2 A
Answer: The current flowing through the resistor is 2 Amperes.
Example 2
A current of 5 A flows through a resistor of 8 Ω.
Voltage = I × R
Voltage = 5 × 8 = 40 V
Answer: The required voltage is 40 Volts.
Example 3
A circuit has a voltage of 24 V and a current of 3 A.
Resistance = V / I
Resistance = 24 / 3 = 8 Ω
Answer: The resistance is 8 Ohms.
Applications of Ohm’s Law
Ohm’s Law is widely used in electrical and electronic engineering.
Some common applications include:
- Designing electrical circuits
- Calculating current in household wiring
- Selecting suitable resistors
- Battery analysis
- LED circuit design
- Mobile charger circuits
- Power supply design
- Industrial electrical systems
- Automotive electrical circuits
Limitations of Ohm’s Law
Ohm’s Law is not applicable to:
- Diodes
- Transistors
- Thermistors
- Filament lamps at varying temperatures
- Electrolytes
- Gas discharge tubes
These devices do not have a constant resistance.
Advantages of Ohm’s Law
- Simple and easy to understand
- Forms the basis of circuit analysis
- Useful in designing electrical systems
- Helps calculate voltage, current, and resistance quickly
Key Points to Remember
- Voltage is directly proportional to current.
- Current is inversely proportional to resistance.
- Resistance opposes the flow of current.
- The law is valid only when temperature remains constant.
Frequently Asked Questions (FAQs)
1. Who discovered Ohm’s Law?
Ohm’s Law was discovered by Georg Simon Ohm in 1827.
2. What is the formula for Ohm’s Law?
V = I × R
3. What is the SI unit of resistance?
The SI unit of resistance is Ohm (Ω).
4. Why is Ohm’s Law important?
It helps engineers and students calculate voltage, current, and resistance in electrical circuits and is fundamental to electrical engineering.
Conclusion
Ohm’s Law is the foundation of electrical engineering because it explains the relationship between voltage, current, and resistance. Whether you are designing a circuit, troubleshooting electrical equipment, or learning the basics of electricity, understanding Ohm’s Law is essential. Mastering this simple relationship will make it much easier to study advanced electrical and electronic engineering topics.
