The opposition offered to the flow of current in an AC circuit because of resistance, capacitance and inductance is known as Impedance. Resistance is the contribution of the resistive element in the circuit, whereas the contribution of both resistance and reactance forms Impedance. Resistance is denoted by R whereas impedance by Z.
Resistance is a simple value consisting of only real numbers. Example: 3. Impedance comprise of both real and imaginary numbers. The Resistance of the circuit does not vary according to the frequency of AC or DC, whereas Impedance varies with the change in frequency.
Because it only affects changing current, reactance is specific to AC power and depends on the frequency of the current. When reactance is present, it creates a 90 degree phase shift between voltage and current, with the direction of the shift depending on whether the component is an inductor or a capacitor. Reactance that occurs in an inductor is known as inductive reactance.
When inductive reactance is present, energy is stored in the form of a changing magnetic field, and the current waveform lags the voltage waveform by 90 degrees. Inductive reactance is caused by devices in which wire is wound circularly — such as coils including line reactors , chokes , and transformers.
Reactance that occurs in a capacitor is known as capacitive reactance. Capacitive reactance stores energy in the form of a changing electrical field and causes current to lead voltage by 90 degrees. Capacitance is created when two conducting plates are placed parallel to one another with a small distance between them, filled with a dielectric material insulator. In metals such as silver or copper , which have high electrical conductivity and therefore low resistivity, electrons are able to skip freely from one atom to the next, with little resistance.
The electrical resistance of a circuit component is defined as the ratio of the applied voltage to the electric current that flows through it, according to HyperPhysics , a physics resource website hosted by the department of physics and astronomy at Georgia State University. The standard unit for resistance is the ohm, which is named after German physicist Georg Simon Ohm. It is defined as the resistance in a circuit with a current of 1 ampere at 1 volt.
Resistors are generally classified as either fixed or variable. Fixed-value resistors are simple passive components that always have the same resistance within their prescribed current and voltage limits.
They are available in a wide range of resistance values, from less than 1 ohm to several million ohms. Variable resistors are simple electromechanical devices, such as volume controls and dimmer switches, which change the effective length or effective temperature of a resistor when you turn a knob or move a slide control. An inductor is an electronic component consisting of a coil of wire with an electric current running through it, creating a magnetic field. The unit for inductance is the henry H , named after Joseph Henry , an American physicist who discovered inductance independently at about the same time as English physicist Michael Faraday.
One henry is the amount of inductance that is required to induce 1 volt of electromotive force the electrical pressure from an energy source when the current is changing at 1 ampere per second.
One important application of inductors in active circuits is that they tend to block high-frequency signals while letting lower-frequency oscillations pass. Note that this is the opposite function of capacitors.
Combining the two components in a circuit can selectively filter or generate oscillations of almost any desired frequency. With the advent of integrated circuits, such as microchips, inductors are becoming less common, because 3D coils are extremely difficult to fabricate in 2D printed circuits.
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