RESISTORS

A resistor is a two-terminal passive electronic component that limits, regulates, or restricts the flow of electric current in a circuit

If too much electricity flows, components can overheat, LEDs can burn out, and circuits can get damaged.

A resistor protects components by limiting current, dividing voltage, and controlling signal levels in a circuit.

Measured in ohms, they convert electrical energy into heat to protect components, divide voltages, and bias active elements.

Very Simple Example

If you connect an LED directly to a battery, it may burn out because too much current flows through it.

But if you add a resistor in series, it reduces the current, keeps the LED safe, and allows it to glow properly.

Resistance is the property of a material to oppose the flow of electric current.

The resistance (R) of a conductor depends on:

The mathematical expression is:

R = ρ (L / A)

Where:

Resistance is measured in Ohms (Ω).

Resistors are mainly classified into two types:

Fixed resistors have a constant resistance value that cannot be changed.

Carbon Composition: Made from a mixture of carbon granules and a binding material.
Carbon Film: A thin layer of carbon is deposited on an insulating core. The resistance value depends on the thickness of the carbon film.
Metal Film: Similar to carbon film but uses metal (such as Nichrome). It provides better stability, accuracy, and lower noise.
Wire-Wound: Constructed by winding a metal wire (usually Manganin or Nichrome) around an insulating core.

Variable resistors allow the resistance value to be adjusted manually.

Potentiometer: A three-terminal device used as a voltage divider. It uses a sliding contact called a wiper to vary resistance.
Rheostat: Usually a two-terminal variable resistor used to control current in a circuit.
Trimmers (Presets): Small variable resistors used for occasional adjustments and calibration on circuit boards.