A resistor is an electrical component that limits or regulates the flow of electrical current in an electronic circuit. They are passive components that create resistance in the flow of electric current. Resistors can be used for many purposes, including:

• Limiting current: One of the most common uses of a resistor is to limit the amount of current in part of a circuit. Too much current can destroy many sensitive electronic components such as transistors and integrated circuits. By putting a resistor at the input to a sensitive part, you limit the current that reaches the part.

• Dividing voltage: Resistors can be used to reduce the voltage supplied to different parts of a circuit. For instance, if you have a 9-volt power supply but you need to provide 5 volts to power a particular integrated circuit, you can set up a circuit to divide the voltage in a way that provides 5 V at the output.

• Heating: Resistors generate heat when conducting current, so they are used in heating appliances such as heaters, toasters, microwaves, and electric stoves.

• Frequency and timing: Resistors can be used in electronic sirens, blinking lights used in airplanes or tall towers, and light flashers. They work on the principle of filling up current to a certain time and then discharge light. In this case, the resistor decides how much current has to be passed according to the time allotted.

• Matching and loading circuits: Resistors can be used to match the impedance of different parts of a circuit, or to load a circuit to achieve a desired response.

• Gain control: Resistors can be used to control the gain of an amplifier.

• Setting time constants: Resistors can be used to set the time constant of a circuit.

• Terminating transmission lines: Resistors can be used to terminate transmission lines.

Resistors are also used to protect components against voltage spikes, provide the proper voltage, and dissipate kinetic energy from trains. They are commercially available with resistance values over a range of more than nine orders of magnitude.