Resistor

A resistor is a two-terminal electrical or electronic component that resists an electric current by producing a voltage drop between its terminals in accordance with Ohm's law. : The electrical resistance is equal to the voltage drop across the resistor divided by the current through the resistor. Resistors are used as part of electrical networks and electronic circuits.

A resistor is used to create a known voltage-to-current ratio in an electric circuit. If the current in a circuit is known, then a resistor can be used to create a known potential difference proportional to that current. Conversely, if the potential difference between two points in a circuit is known, a resistor can be used to create a known current proportional to that difference. Current-limiting.

By placing a resistor in series with another component, such as a light-emitting diode, the current through that component is reduced to a known safe value. A series resistor can be used for speed regulation of DC motors, such as used on locomotives and trainsets. An attenuator is a network of two or more resistors (a voltage divider) used to reduce the voltage of a signal.

A line terminator is a resistor at the end of a transmission line or daisy chain bus (such as in SCSI), designed to match impedance and hence minimize reflections of the signal. All resistors dissipate heat. This is the principle behind electric heaters. (See also electric heating and resistive heating)