Electricity Basics: Resistance, Inductance & Capacitance
Write the formulas for inductive and capacitive reactances. 5. Write the formula for impedance, and calculate the impedance in a series circuit when the values. Capacitors and Inductors For resistive circuits, the voltage-current The relationship between the capacitance, the charge and the voltage is. circuit and explain its relationship to the performance of the circuit. • Energy stored in an inductor. • Definition of capacitance and Continuity condition for.
It has no affect when the current is constant.
Inductance only has an effect when the current is changing as in an AC circuit. Inductance is measured in Henrys. The symbol for inductance is a series of coils as shown below. The letter "L" is used in equations. Inductor Symbol Interesting Facts about Resistors, Capacitors, and Inductors The resistance of a material is the opposite or the inverse of the conductivity.
The Ohm is named after German physicist Georg Ohm.
The Farad is named after English physicist Michael Faraday. The Henry is named after American scientist Joseph Henry. Combinations of capacitors, inductors, and resistors are used to build passive filters that will only allow electronic signals of certain frequencies to pass through. Activities Take a ten question quiz about this page. It is defined as the resistance in a circuit with a current of one ampere at one volt.
One way to understand Ohm's Law is to hold one of these variables constant, change the value of another variable, and watch what happens to the third variable.
Electricity Basics: Resistance, Inductance & Capacitance
For instance, if we keep voltage constant and increase the resistance, the current must decrease. If we keep the resistance constant and increase the voltage, the current must increase. 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 with tolerances ranging from plus or minus 0.
Series R, L, and C
Resistors are also classified by the maximum voltage they can tolerate as well as the maximum amount of power they can dissipate. All other things being equal, a resistor that is twice as long will have twice the resistance, and one with twice the cross-sectional areal will have half the resistance. Also, material with higher resistivity will result in proportionally greater resistance.
Variable resistors are simple electro-mechanical devices, such as volume controls and dimmer switches, which increase the effective length of a resistor by turning a knob or moving a slide control. Strain gauges are resistors in which resistance changes with strain.
Strain occurs when an object is stretched or compressed. A thermistor is a temperature sensor. It changes resistance when an increase in temperature excites electrons, making them available to conduct current, thus reducing the resistivity of the material. A piezoresistor changes its resistivity in response to a change in strain, which causes more or fewer electrons to be available to carry charge.
Inductance An inductor is an electronic component consisting simply of a coil of wire. A constant electric current running through an inductor produces a magnetic field. If the current changes, so does the magnetic field. The unit for inductance is the henry Hnamed after Joseph Henryan 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 one volt of electromotive force when the current is changing at one ampere per second. Finally, Lenz's lawnamed after Russian physicist Heinrich Lenzstates that this induced current is in the opposite direction of the change in current that produced the magnetic field.
This phenomenon is called self-inductance.
Series R, L, and C | Reactance And Impedance -- R, L, And C | Electronics Textbook
What this means is, if you quickly reduce the current through the inductor, the changing magnetic field will induce a current that opposes the change, which tends to maintain the current at its previous level. Conversely, if you increase the current sharply, the induced current will be in the opposite direction of the increase, which again tends to maintain the current at a constant level. In other words, an inductor creates a kind of inertia in the current flow that resists rapid changes in much the same way that a massive body resists changes in its velocity.
Being a series circuit, current must be equal through all components. Thus, we can take the figure obtained for total current and distribute it to each of the other columns: Notice something strange here: How can this be?
The answer lies in the interaction between the inductive and capacitive reactances. Expressed as impedances, we can see that the inductor opposes current in a manner precisely opposite that of the capacitor. When these two contrary impedances are added in seriesthey tend to cancel each other out!
It is analogous to adding together a positive and a negative scalar number: If the total impedance in a series circuit with both inductive and capacitive elements is less than the impedance of either element separately, then the total current in that circuit must be greater than what it would be with only the inductive or only the capacitive elements there.
With this abnormally high current through each of the components, voltages greater than the source voltage may be obtained across some of the individual components!