### Why is Resistance Required?

Resistance is required for a variety of reasons, including:

• To control the flow of current: Resistance is used to limit or control the flow of electric current in a circuit. This is necessary because excessive current flow can damage or destroy components in the circuit.
• To generate heat: Resistance can be used to generate heat, which is useful in many applications such as electric heaters, stoves, and ovens.
• To divide voltage: Resistors are often used to divide voltage in a circuit. This is useful when different components in the circuit require different voltage levels to operate properly.
• To convert electrical energy into other forms of energy: Resistors can be used to convert electrical energy into other forms of energy such as heat or light. This is useful in applications such as incandescent light bulbs and electric heaters.
• To protect components: Resistors can be used to protect other components in a circuit from damage due to excessive current flow or voltage spikes. For example, a surge protector uses a resistor to limit voltage spikes and protect connected devices from damage.

Overall, resistance is an essential property of electric circuits and plays a critical role in many important applications.

### Ohm’s Law

The law of Ohm is a fundamental principle in electronics that describes the relationship between resistance, current, and voltage in a circuit. According to Ohm’s law, the current through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance between them. Mathematically, this can be expressed as:

I = V/R

Where I is the current in the circuit, V is the voltage applied to the circuit, and R is the resistance of the circuit.

To better understand the law of Ohm, consider a practical example of a circuit consisting of a battery, a resistor, and an LED. The battery provides a voltage source to power the LED, and the resistor is used to limit the current flowing through the LED.

Suppose the voltage of the battery is 9V, and the resistance of the circuit is 100 ohms. Using Ohm’s law, we can calculate the current flowing through the circuit as follows:

I = V/R

I = 9/100

I = 0.09 amps or 90 milliamps

This means that 90 milliamps of current is flowing through the circuit. By changing the resistance of the circuit, we can change the current flowing through the LED. For example, if we increase the resistance to 200 ohms, the current flowing through the LED will be:

I = V/R

I = 9/200

I = 0.045 amps or 45 milliamps

This means that by increasing the resistance, we have effectively reduced the current flowing through the LED, which can help protect it from damage.

Overall, Ohm’s law is a fundamental principle that is essential for understanding the behavior of electronic circuits. By understanding the relationship between resistance, current, and voltage, engineers and technicians can design and troubleshoot circuits with confidence, and ensure that they are operating within safe and reliable parameters.