B-005
Subelement B-005
Section B-005-010
Section B-005-010
How does an inductor react to AC?
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Correct AnswerAs the frequency of the applied AC increases, the reactance increases
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As the amplitude of the applied AC increases, the reactance increases
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As the amplitude of the applied AC increases, the reactance decreases
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As the frequency of the applied AC increases, the reactance decreases
Reactance is opposition. XL = 2 * PI * f * L. Inductive reactance = two times PI (i.e., 3.14) times frequency in hertz times inductance in henries. Reactance (opposition) is not influenced by the amplitude of the applied voltage. If frequency goes up, inductive reactance goes up. Intuitively, the higher the frequency (i.e., rate of change), the more significant become the counter-currents induced in adjacent turns.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
How does a capacitor react to AC?
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As the amplitude of the applied AC increases, the reactance decreases
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As the amplitude of the applied AC increases, the reactance increases
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Correct AnswerAs the frequency of the applied AC increases, the reactance decreases
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As the frequency of the applied AC increases, the reactance increases
Reactance is opposition. XC = 1 over ( 2 * PI * f * C ). Capacitive Reactance = 1 over the product of 'two times PI (i.e., 3.14) times frequency in hertz times capacitance in farads'. A behaviour opposite to inductors. Reactance (opposition) is not influenced by the amplitude of the applied voltage. If frequency goes up, capacitive reactance goes down. Intuitively, the more frequent the change of polarity (AC changes polarity every half-cycle), the more incessant becomes the charge/discharge current, current never seems to stop, less apparent opposition to current flow.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
The reactance of capacitors increases as:
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applied voltage increases
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applied voltage decreases
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frequency increases
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Correct Answerfrequency decreases
Reactance is opposition. XC = 1 over ( 2 * PI * f * C ). Capacitive Reactance = 1 over the product of 'two times PI (i.e., 3.14) times frequency in hertz times capacitance in farads'. A behaviour opposite to inductors. Reactance (opposition) is not influenced by the amplitude of the applied voltage. If frequency goes up, capacitive reactance goes down. Intuitively, the more frequent the change in polarity (AC changes polarity every half-cycle), the more incessant becomes the charge/discharge current, current never seems to stop, less apparent opposition to current flow.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
What is the term for the opposition to alternating current caused by the combined effect of reactance and resistance?
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Admittance
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Conductance
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Correct AnswerImpedance
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Reluctance
Impedance (Z) is measured in ohms. It is the combined effect of reactance(s) and resistance. Resistance affects DC and AC equally. Reactance is a property only present under AC. [ DC = direct current, AC = alternating current ]. Impedance (Z) can also be seen as the ratio of voltage to current in AC circuits: Z = E / I. Generally, high impedance circuits function at high voltages and low currents, while low impedance circuits use low voltages at high currents.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
What term equals the ratio of AC voltage to AC current in a system or circuit?
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Conductance
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Resistance
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Correct AnswerImpedance
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Reactance
Impedance (Z) is measured in ohms. It is the combined effect of reactance(s) and resistance. Resistance affects DC and AC equally. Reactance is a property only present under AC. [ DC = direct current, AC = alternating current ]. Impedance (Z) can also be seen as the ratio of voltage to current in AC circuits: Z = E / I. Generally, high impedance circuits function at high voltages and low currents, while low impedance circuits use low voltages at high currents.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
What circuit parameter change causes an inductor's reactance to increase?
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A decrease in frequency
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An increase in current
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An increase in voltage
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Correct AnswerAn increase in frequency
Reactance is opposition. XL = 2 * PI * f * L. Inductive reactance = two times PI (i.e., 3.14) times frequency in hertz times inductance in henries. Reactance (opposition) is not influenced by the amplitude of the applied voltage. If frequency goes up, inductive reactance goes up. Intuitively, the higher the frequency (i.e., rate of change), the more significant become the counter-currents induced in adjacent turns.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
What property allows a coil wound on a ferrite core to mitigate the effects of an offending radio signal?
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Correct AnswerHigh reactance at radio frequencies
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Low reactance at audio frequencies
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High reactance at audio frequencies
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Low reactance at radio frequencies
The coil (inductor) when dealing with an offending radio signal: chokes off radio frequency (high reactance), but passes audio frequencies (low reactance). Recall that the opposition of a coil to AC current flow (inductive reactance) grows as frequency increases.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
What property allows a bypass capacitor in an audio circuit to divert an interfering RF signal?
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High reactance at radio frequencies
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Low reactance at audio frequencies
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High reactance at audio frequencies
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Correct AnswerLow reactance at radio frequencies
The bypass capacitor must provide a low impedance path for an offending signal without affecting lower frequency signals: low reactance for radio frequency, high reactance for audio. Recall that the opposition of a capacitor to AC current flow (capacitive reactance) decreases as frequency goes up.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
What property allows an RF bypass capacitor to have little effect on an audio circuit?
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High reactance at radio frequencies
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Low reactance at audio frequencies
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Low reactance at radio frequencies
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Correct AnswerHigh reactance at audio frequencies
The bypass capacitor must provide a low impedance path for an offending signal without affecting lower frequency signals: low reactance for radio frequency, high reactance for audio. Recall that the opposition of a capacitor to AC current flow (capacitive reactance) decreases as frequency goes up.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
What property allows an RF choke coil to have little effect on signals meant to flow through the coil?
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Low reactance at high frequencies
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Correct AnswerLow reactance at low frequencies
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High reactance at high frequencies
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High reactance at low frequencies
The coil (inductor) when dealing with an offending radio signal: chokes off radio frequency (high reactance), but passes audio frequencies (low reactance). Recall that the opposition of a coil to AC current flow (inductive reactance) grows as frequency increases.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
In general, the reactance of inductors increases with:
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decreasing applied voltage
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increasing applied voltage
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decreasing AC frequency
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Correct Answerincreasing AC frequency
Reactance is opposition. XL = 2 * PI * f * L. Inductive reactance = two times PI (i.e., 3.14) times frequency in hertz times inductance in henries. Reactance (opposition) is not influenced by the amplitude of the applied voltage. If frequency goes up, inductive reactance goes up. Intuitively, the higher the frequency (i.e., rate of change), the more significant become the counter-currents induced in adjacent turns.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
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