Question

Why Ohm's law is not applicable for nonlinear circuit?

Answer 1

Ohm's law states that the voltage across a conductor is directly proportional to the current flowing through it, with the proportionality constant being the resistance, i.e., \( V = IR \), where \( V \) is voltage, \( I \) is current, and \( R \) is the resistance.

This law assumes that the resistance \( R \) is constant. However, in nonlinear circuits, the relationship between voltage and current is not linear, meaning the resistance can change depending on the voltage or current. Here’s why Ohm's law doesn't apply in these cases:

### 1. **Nonlinear Resistance:**
   In nonlinear components (like diodes, transistors, or certain resistors), the resistance isn't constant. For example, in a diode, the current-voltage relationship follows an exponential curve, not a straight line. This means that as the voltage changes, the resistance of the diode also changes, making the simple linear relationship in Ohm’s law invalid.

### 2. **Voltage-Current Relationship:**
   In nonlinear circuits, the voltage and current do not follow a simple linear proportionality. For instance, in a diode, the current increases exponentially with voltage, unlike a resistor where the current increases linearly with voltage. Therefore, you can’t apply the formula \( V = IR \) directly because the relationship isn’t linear.

### 3. **Dynamic Behavior:**
   Nonlinear components may exhibit complex behavior such as hysteresis or frequency-dependent responses, which further complicates the use of Ohm’s law.

### In summary:
Ohm's law is only valid for circuits where the relationship between voltage and current is linear, i.e., where the resistance remains constant. In nonlinear circuits, the voltage and current do not have a fixed, proportional relationship, so Ohm's law doesn’t apply.