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Old Monday, February 22, 2010
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Default basic electronics short questions


Question 42: How are electrolytic capacitors constructed, and what is particularly noteworthy about their use?
╦lectrolytic" capacitors use a very thin layer of metal oxide as the dielectric. The manufacturing process involves applying a DC voltage to the new capacitor to create the oxide layer. This "polarizes" it for life, preventing its use with reverse polarity.
Follow-up question: identify the schematic symbol for any type of polarized capacitor, electrolytics included.
Question 41: A capacitor has a label on it saying, "100 WVDC". What does this label mean? What is the consequence of exceeding this rating?
Answer :The capacitor's working voltage is 100 volts DC. Failure of the dielectric material will result from exceeding this voltage rating. In electrolytic capacitors especially, the failure can be violent!
Question 40: Capacitors may pose an electric shock hazard, even in unpowered circuits. Explain why.
Answer: Capacitors have the ability to store dangerous voltage and charge levels even when external energy sources have been disconnected.
Question 39: A 10 μF capacitor is charged to a voltage of 20 volts. How many coulombs of electric charge are stored in this capacitor?
Answer :200 μC of charge. :

When checked with an ohmmeter, how should a properly functioning capacitor respond?
Answer : A "healthy" capacitor should register as an open circuit between its terminals, after the initial charging period.

A 5 H inductor is subjected to an electric current that changes at a rate of 4.5 amps per second. How much voltage will be dropped by the inductor?
Answer :This inductor will drop 22.5 volts.
When checked with an ohmmeter, how should a properly functioning inductor respond?
Answer :A "healthy" inductor should register as a very low resistance between its terminals. If the inductor has an iron core, there should be infinite resistance (no continuity) between either winding terminal and the core.
than the other.

How is it possible to assign a fixed value of voltage or current (such as "120 volts") to an AC electrical quantity that is constantly changing, crossing 0 volts, and reversing polarity?
We may express quantities of AC voltage and current in terms of peak, peak-to-peak, average, or RMS.
Suppose a DC power source with a voltage of 50 volts is connected to a 10 Ω load. How much power will this load dissipate? [/Now suppose the same 10 Ω load is connected to a sinusoidal AC power source with a peak voltage of 50 volts. Will the load dissipate the same amount of power, more power, or less power? Explain your answer.
Answer :50 volts DC applied to a 10 Ω load will dissipate 250 watts of power. 50 volts (peak, sinusoidal) AC will deliver less than 250 watts to the same load.
Is the deflection of an analog AC meter movement proportional to the peak, average, or RMS value of the waveform measured? Explain your answer. Answer :Analog meter deflection is proportional to the average value of the AC waveform measured, for most AC meter movement types. There are some meter movement designs, however, that give indications proportional to the RMS value of the waveform: hot-wire and electrodynamometer movements are of this nature.

In calculating the size of wire necessary to carry alternating current to a high-power load, which type of measurement is the best to use for current: peak, average, or RMS? Explain why.
Answer :RMS current is the most appropriate type of measurement for calculating wire size.

In calculating the thickness of insulators for high-voltage AC power lines, which type of measurement is the best to use for voltage: peak, average, or RMS? Explain why.
Answer : Peak voltage is the most appropriate type of measurement for calculating insulator thickness. The reason why has to do with the time required for an insulator to "flash over."
As a general rule, capacitors oppose change in (choose: voltage or current), and they do so by . . . (complete the sentence).
Based on this rule, determine how a capacitor would react to a constant AC voltage that increases in frequency. Would an capacitor pass more or less current, given a greater frequency? Explain your answer.
Answer :As a general rule, capacitors oppose change in voltage, and they do so by producing a current.
A capacitor will pass a greater amount of AC current, given the same AC voltage, at a greater frequency.
Does a capacitor's opposition to alternating current increase or decrease as the frequency of that current increases? Also, explain why we refer to this opposition of AC current in a capacitor as reactance instead of resistance.
Answer : The opposition to AC current ("reactance") of a capacitor decreases as frequency increases. We refer to this opposition as "reactance" rather than "resistance" because it is non-dissipative in nature. In other words, reactance causes no power to leave the circuiSuppose someone were to ask you to differentiate electrical reactance (X) from electrical resistance (R). How would you distinguish these two similar concepts from one another, using your own words?
Answer :t is really important for you to frame this concept in your own words, so be sure to check with your instructor on the accuracy of your answer to this question! To give you a place to start, I offer this distinction: resistance is electrical friction, whereas reactance is electrical energy storage. Fundamentally, the difference between X and R is a matter of energy exchange, and it is understood most accurately in those terms.
As a general rule, inductors oppose change in (choose: voltage or current), and they do so by . . . (complete the sentence).
Based on this rule, determine how an inductor would react to a constant AC current that increases in frequency. Would an inductor drop more or less voltage, given a greater frequency? Explain your answer.
Answer :As a general rule, inductors oppose change in current, and they do so by producing a voltage.
An inductor will drop a greater amount of AC voltage, given the same AC current, at a greater frequency. . Does an inductor's opposition to alternating current increase or decrease as the frequency of that current increases? Also, explain why we refer to this opposition of AC current in an inductor as reactance instead of resistance.
Answer :The opposition to AC current ("reactance") of an inductor increases as frequency increases. We refer to this opposition as "reactance" rather than "resistance" because it is non-dissipative in nature. In other words, reactance causes no power to leave the circuit.
Capacitance is a very important property in many types of electric circuits.Define what "capacitance" is, and what causes it.
Answer :"Capacitance" is the capacity of two separated conductors to store energy in the form of an electric field, resulting from an applied voltage. You may also find a definition of "capacitance" stated in terms of opposition to change in applied voltage over time.
Capacitance is caused by the establishment of an electric field between two conductors.What are the differences between voltage and current controlled devices?In any (electronic) device controlling parameter is current it is called current controlled device. eg bilpolar transistor- output current is a function of base current.

In any (electronic) device controlling parameter is voltage it is called voltage controlled device. eg Field effect transistor- output current is a function of gate voltage.

It depends on the inherent physical mechanism which defines the primary (independent) controlling parameter.


[An inductor rated at 4 Henrys is subjected to a sinusoidal AC voltage of 24 volts RMS, at a frequency of 60 hertz. Write the formula for calculating inductive reactance (XL), and solve for current through the inductor.
Answe

XL = 2 πf L

The current through this inductor is 15.92 mA RMS.
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Last edited by Kamran Chaudhary; Tuesday, April 23, 2013 at 06:36 PM. Reason: red fonts
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