Ohm's law
Ohm's Law
Ohm's Law is a fundamental principle in the field of electrical engineering and physics that describes the relationship between voltage, current, and resistance in an electrical circuit. It is named after the German physicist Georg Simon Ohm who first formulated the law in 1827.
The Basic Principle
Ohm's Law states that the current flowing through a conductor between two points is directly proportional to the voltage across the two points, provided the temperature remains constant. This relationship can be expressed with the following formula:
[ I = \frac{V}{R} ]
Where:
- ( I ) is the current in amperes (A)
- ( V ) is the voltage in volts (V)
- ( R ) is the resistance in ohms (Ω)
Formulas Derived from Ohm's Law
Ohm's Law can be rearranged to solve for voltage or resistance:
[ V = I \times R ]
[ R = \frac{V}{I} ]
Important Points and Differences
| Property | Symbol | Unit | Relation to Ohm's Law |
|---|---|---|---|
| Voltage (V) | V | Volts (V) | V = I × R |
| Current (I) | I | Amperes (A) | I = V / R |
| Resistance (R) | R | Ohms (Ω) | R = V / I |
- Voltage (V): The electric potential difference between two points. It is the cause that pushes the current through the resistance.
- Current (I): The flow of electric charge. It is the effect of the voltage applied across a resistance.
- Resistance (R): The opposition to the flow of current. It is a property of the material that composes the conductor.
Examples to Explain Ohm's Law
Example 1: Calculating Current
Suppose you have a 9V battery connected to a resistor with a resistance of 3Ω. To find the current flowing through the resistor, you can use Ohm's Law:
[ I = \frac{V}{R} = \frac{9V}{3Ω} = 3A ]
So, a current of 3 amperes will flow through the resistor.
Example 2: Calculating Voltage
If you know that a current of 2A is flowing through a resistor with a resistance of 5Ω, you can calculate the voltage across the resistor:
[ V = I \times R = 2A \times 5Ω = 10V ]
The voltage across the resistor is 10 volts.
Example 3: Calculating Resistance
If there is a voltage of 12V across a resistor and the current flowing through it is 4A, the resistance can be calculated as:
[ R = \frac{V}{I} = \frac{12V}{4A} = 3Ω ]
The resistance of the resistor is 3 ohms.
Limitations of Ohm's Law
Ohm's Law is not universal and has limitations. It applies to materials that are ohmic, meaning they have a constant resistance regardless of the voltage and current. However, some materials and devices do not follow Ohm's Law. These are called non-ohmic and include:
- Diodes and transistors, which have a non-linear V-I characteristic.
- Materials that change their resistance with temperature, light, or other factors.
Conclusion
Ohm's Law is a key concept in understanding how electrical circuits operate. It provides a simple relationship between voltage, current, and resistance, which can be used to analyze and design circuits. However, it is important to recognize its limitations and the conditions under which it can be accurately applied.