Enter the Desired Current, I: The factors that determine the resistance value of the resistor are the supply voltage, V Sthe forward voltage drop needed for the LED, V Fand the desired current wanted to pass through the LED.
Perhaps the easiest variable in any circuit to control is its resistance. This can be done by changing the material, size, and shape of its conductive components remember how the thin metal filament of a lamp created more electrical resistance than a thick wire? What is a Resistor? Special components called resistors are made for the express purpose of creating a precise quantity of resistance for insertion into a circuit.
They are typically constructed of metal wire or carbon, and engineered to maintain a stable resistance value over a wide range of environmental conditions. Unlike lamps, they do not produce light, but they do produce heat as electric power is dissipated by them in a working circuit.
Typically, though, the purpose of a resistor is not to produce usable heat, but simply to provide a precise quantity of electrical resistance. Resistor Schematic Symbols The most common schematic symbol for a resistor is a zig-zag line: Resistor values in ohms are usually shown as an adjacent number, and if several resistors are present in a circuit, they will be labeled with a unique identifier number such as R1, R2, R3, etc.
As you can see, resistor symbols can be shown either horizontally or vertically: Real resistors look nothing like the zig-zag symbol. Instead, they look like small tubes or cylinders with two wires protruding for connection to a circuit. Here is a sampling of different kinds and sizes of resistors: In keeping more with their physical appearance, an alternative schematic symbol for a resistor looks like a small, rectangular box: Resistors can also be shown to have varying rather than fixed resistances.
This might be for the purpose of describing an actual physical device designed for the purpose of providing an adjustable resistance, or it could be to show some component that just happens to have an unstable resistance: In fact, any time you see a component symbol drawn with a diagonal arrow through it, that component has a variable rather than a fixed value.
Variable Resistors Variable resistors must have some physical means of adjustment, either a rotating shaft or lever that can be moved to vary the amount of electrical resistance.
Here is a photograph showing some devices called potentiometers, which can be used as variable resistors: The power rating of any resistor is roughly proportional to its physical size. Note in the first resistor photograph how the power ratings relate with size: Also, note how resistances in ohms have nothing to do with size!
Although it may seem pointless now to have a device doing nothing but resisting electric current, resistors are extremely useful devices in circuits. How are Resistors Useful? It is a picture of a printed circuit board, or PCB: Inserting the known quantities of voltage E and current I into these two equations, we can determine circuit resistance R and power dissipation P: If we were designing a circuit to operate at these values, we would have to specify a resistor with a minimum power rating of 20 watts, or else it would overheat and fail.
Resistor Materials Resistors can be found in a variety of different materials, each one with its own properties and specific areas of use. Most electrical engineers use the types found below: Wirewound WW Wire Wound Resistors are manufactured by winding resistance wire around a non-conductive core in a spiral.
They are typically produced for high precision and power applications. The core is usually made of ceramic or fiberglass and the resistance wire is made of nickel-chromium alloy and are not suitable for applications with frequencies higher than 50kHz. Low noise and stability with respect to temperature variations are standard characteristics of Wire Wound Resistors.
Resistance values are available from 0. Metal Film Nichrome or tantalum nitride are typically used for metal film resistors. A combination of a ceramic material and a metal typically make up the resistive material. The resistance value is changed by cutting a spiral pattern in them film, much like carbon film with a laser or abrasive.
Metal film resistors are usually less stable over temperature than wire wound resistors, but handle higher frequencies better. Metal Oxide Film Metal oxide resistors use metal oxides such as tin oxide, making them slightly different from metal film resistors.
These resistors are reliable and stable and operate at higher temperatures than metal film resistors. Because of this, metal oxide film resistors are used in applications that require high endurance. A ceramic substrate that has a thin bulk metal foil cemented to it makes up the resistive element.
Foil Resistors feature a very low temperature coefficient of resistance. A mixture of fine carbon particles and non-conductive ceramic material are used for the resistive element of CCR Resistors. The substance is molded into the shape of a cylinder and baked.UNIT 1: Basic Laws: Ohm’s law, Kirchhoff’s voltage and current laws, Nodes-Branches and loops, Series elements and Voltage Division, Parallel elements and Current Division.
Resistor color code chart. The chart below shows how to determine the resistance and tolerance for resistors. The table can also be used to specify the color of the bands when the values are known. Ohm's law calculator calculation calculate ohms power formulas mathematical ohm's law pie chart electric voltage drop electric current resistance formula watt's law emf magic triangle tip online voltage volts resistor resistance amps amperes audio engineering E V = I R - P = V I calc conductivity resistivity relation relationship - Eberhard Sengpiel sengpielaudio.
One of the most common mistakes made by beginning electronics students in their application of Ohm’s that the resistance in question is the equivalent of a single resistor “table” method presented for both series and parallel circuits in this chapter is a good way to keep the context of Ohm’s .
Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points. Introducing the constant of proportionality, the resistance, one arrives at the usual mathematical equation that describes this relationship: =, where I is the current through the conductor in units of amperes, V is the voltage measured across the conductor in.
The unit for resistance is an ohm and is given the symbol (upper case In a simple circuit (one with a single simple resistor), the voltage supplied by the source equals the voltage drop across the resistor, since a type of a material for which Ohm’s law is valid simple circuit a circuit with a single voltage source and a single.