The resistor is a passive electrical component to create resistance in the flow of electric current. In almost all electrical networks and electronic circuits they can be found. The resistance is measured in ohms. An ohm is the resistance that occurs when a current of one ampere passes through a resistor with a one volt drop across its terminals. The current is proportional to the voltage across the terminal ends. This ratio is represented by Ohm’s law: Resistors are used for many purposes. A few examples include delimit electric current, voltage division, heat generation, matching and loading circuits, control gain, and fix time constants. They are commercially available with resistance values over a range of more than nine orders of magnitude. They can be used to as electric brakes to dissipate kinetic energy from trains, or be smaller than a square millimeter for electronics. Resistor definition and symbol A resistor is a passive electrical component with the primary function to limit the flow of electric current. The international IEC symbol is a rectangular shape. In the USA the ANSI standard is very common, this is a zigzag line (shown on the right). Overview of types and materials Resistors can be divided in construction type as well as resistance material. The following breakdown for the type can be made: Fixed resistors Variable resistors, such as the: Potentiometer Rheostat Trimpot Resistance dependent on a physical quantity: Thermistors (NTC and PTC) as a result of temperature change Photo resistor (LDR) as a result of a changing light level Varistor (VDR) as a result of a changing voltage Magneto resistor (MDR) as a result of a changing magnetic field Strain Gauges as a result of mechanical load For each of these types a standard symbol exists. Another breakdown based on the material and manufacturing [… read more]

## Resistor fundamentals

What is a resistor? Resistors are passive electrical components that reduce the flow of electrical current in a circuit. They are one of the most common components and can be found in almost every electrical networks and electronic circuit. The resistance is expressed in ohms. There are many different resistor types and constructions. They applications for resistors vary widely: generating heat, delimit current or create a voltage drop, measure physical quantities are only a few examples. Ohms law Ohm’s law is one of the most elementary equations used in electrical engineering. The law was found by Georg Ohm in 1827, and it describes the relation between voltage, current and resistance. When a current passes through a resistor, the voltage drops across the terminals proportionally to the magnitude of resistance: Resistance of a resistor The resistance of a resistor is its primary parameter. Resistance is expressed in Ohm (Ω) and is dependent on the shape of the resistive part and the material properties. The longer the path the current has to travel across the resistor, the higher the resistance will be. The extent to which a material is resistant to electric current is called resistivity. The symbol for resistivity is ρ (W.m). The higher the resistivity of a material, the higher the resistance will be. Good resistor materials have resistivity’s between 2•10^-8 and 200•10^-8 W•m. Kirchhoff law The Kirchhoff circuit laws form the basis of electrical network theory. They are based on the principle of conservation of electrical charge and energy. The Kirchhoff Current Law, or first law, states that the sum of currents from one node is zero. The Kirchhoff Voltage Law, or second law, states the sum of voltage drops and rises in a closed loop of a network is zero. Together with Ohm’s law, the Kirchhoff laws make it [… read more]