Two circuits {coupled circuit} can share impedance, allowing energy transfer.
Circuits {filter circuit} can transmit frequency range, while blocking other frequencies. Filter circuits can remove frequency range, while allowing other frequencies, by differentiating or averaging. Circuits can choose different frequencies {selectivity, filter}. Frequency filtering sharpens edges, because edges have high frequency, and blurs have low frequency.
Circuits {LC circuit} can have inductor and capacitor. Energy flows from inductance magnetic field to capacitance electric field and then from capacitance electric field to inductance magnetic field, at resonance frequency. In resonating circuits, capacitance and inductance reactances are equal, so total reactance equals zero.
Circuits {RC circuit} can have resistor and capacitor. Voltage V depends on time t: V = Vo * e^(-t / (R*C)). Switching on circuit makes voltage build up in capacitor as field builds. Current lags behind voltage. At voltage alternation frequency, circuit resonates.
Circuits {RL circuit} can have inductance and resistor. Current I depends on time t: I = Io * e^(-t * R / L). At switching on, current changes fast, so voltage in coil is high. Then current becomes constant so voltage goes to zero, and current lags behind voltage. At current-alternation frequency, circuit resonates.
Thermionically emitted electrons can travel in beams, under side-electromagnet control, to fluorescent screens, where they excite phosphor crystals to make light {cathode ray tube}|. Cathode ray tubes are in TVs and oscilloscopes.
Circuit devices {detector} can select one signal from several.
Solid-state semiconductor circuit elements or vacuum tubes {diode}| can allow current to flow in only one direction. Diodes change alternating current to direct current. Tubes can have cathode emitter and anode plate. If plate is positive, emitted electrons flow toward plate. If plate is negative, no emitted electrons flow. For solid state, np junction allows charge to flow only in one direction, from P-type to N-type, with high resistance in other direction.
Circuit devices {mixer, signal} {electric circuit, mixer} can combine frequency signals.
Circuit devices {oscillator, circuit}| {electric oscillator} can change voltage waveform to other frequencies and amplitudes.
Devices {rectifier}| can change alternating to direct current.
Devices {rheostat}| can make variable resistance.
Circuit devices {wave shaper} can change voltage waveform.
Sunlight electric potential can make electric current in materials {photocell}|.
Shining light onto selenium {selenium cell} increases conductivity, because light increases electric field.
Instruments {ammeter}| can measure currents.
Instruments {galvanometer}| can measure small currents and current direction.
Instruments {ohmmeter}| can measure resistance.
Instruments {potentiometer}| can measure voltages at zero current, as ratio to exactly known voltage.
Instruments {voltmeter}| can measure electric potentials.
Devices {Wheatstone bridge}| can find resistance or capacitance in circuits using ratios. Wheatstone bridges eliminate voltage effects. AC current negates overall flow effects.
Current from a potential source P splits between two known resistances, R1 and R2, which have a galvanometer G across their endpoints to measure current and voltage (Figure 1). From one endpoint is an adjustable resistance Rv. From the other endpoint is an unknown resistance Rx. The resistances Rv and Rx meet at a point. If the ratio of the adjustable resistance Rv to the first known resistance R1 equals the ratio of the unknown resistance Rx to the second known resistance R2, the galvanometer has zero voltage and current.
For typical resistances, one can set R1 = R2, so Rv = Rx at galvanometer zero current and voltage.
If three resistances are known and one unknown, the measured voltage allows calculating the unknown resistance.
Wheatstone bridges can also find capacitance.
5-Physics-Electromagnetism-Circuit
Outline of Knowledge Database Home Page
Description of Outline of Knowledge Database
Date Modified: 2022.0225