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A comprehensive set of 400 questions and answers related to alternating currents (ac) circuits. It covers various aspects of ac circuits, including capacitance, inductance, reactance, impedance, power factor, transformers, and more. The questions are designed to test understanding of fundamental concepts and practical applications of ac circuits. This resource can be valuable for students studying electrical engineering or related fields.
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Given: A 30-microfarad capacitor in parallel with a 15-microfarad capacitor. The total capacitance is___. - ANSWER✔✔ 45 What is the hertz rating of an AC circuit if the frequency is 20 cycles per 1/2 second? - ANSWER✔✔40Hz Given: A circuit has an rms voltage of 120VAC. What is the peak-to-peak voltage? - ANSWER✔✔340V
A circuit has a peak voltage of 275V. What is the average voltage value?
In AC circuits containing only resistance,. - ANSWER✔✔All DC rules and laws apply, including Ohm's law If the area of the plates of a capacitor is increased, the amount of capacitance. - ANSWER✔✔Increases The self-induced voltage across in inductance is equal to the change in___. - ANSWER✔✔Current with respect to time Unless otherwise noted, the calculations in AC circuits use___. - ANSWER✔✔Rms values When frequency decreases, capacitive reactance___. - ANSWER✔✔Increases
Given: A transformer has 200 turns in the primary, 100 turns in the secondary, and 150V AC applied to the primary. What is the voltage across the secondary? - ANSWER✔✔75V AC Transformers in which the primary and secondary voltages are 180 out of phase are known as___. - ANSWER✔✔Unlike-wound transformers Maximum voltage is generated by rotating wire when the conductor is moving___. - ANSWER✔✔Across the field at 90° If the time for one cycle is 0.1 second, the frequency is___. - ANSWER✔✔10 Hz If the phase angles of two sine waves are both 0 degrees then the waves___. - ANSWER✔✔Are in phase
If the vector diagram of two AC waveforms is a right angle, then the waves___. - ANSWER✔✔Are 90° out of phase In an inductive AC circuit, when the applied voltage is at its maximum negative value, the current is___. - ANSWER✔✔Zero The product of the source voltage and the total current is___. - ANSWER✔✔Apparent power In a parallel LC circuit, the voltage across the branches is___. - ANSWER✔✔The same as the applied voltage Which of the following coils is likely to show the lowest inductance? - ANSWER✔✔A coil with a narrow coil, long core, non-magnetic core and few turns
Which of the following conditions exist in a circuit of pure resistance? - ANSWER✔✔Voltage and current in phase What is the peak voltage in a circuit with an rms voltage of 120VAC? - ANSWER✔✔170 volts Which of the following conditions exist in a circuit of pure inductance? - ANSWER✔✔The voltage and current are 90 degrees out of phase. The power factor in a circuit with a resistance of 50Upper Omega and an impedance of 100Upper Omega is - ANSWER✔✔0. A power factor is not an angular measure, but a numerical ratio with a value between 0 and 1, equal to the - ANSWER✔✔cosine of the phase angle A transformer with 10 turns in the primary and two turns in the secondary has a turns ratio of (ratio is primary/secondary) -
The opposition to current flow offered by the capacitance of a circuit is known as - ANSWER✔✔Capacitive Reactance The total capacitance of two 15uF capacitors in series is - ANSWER✔✔7.5uF The true power in a circuit with 4A through a 50 Omega resistor is - ANSWER✔✔800W An electric current always produces - ANSWER✔✔magnetic field The total capacitance of two 15uF capacitors connected in parallel is - ANSWER✔✔30uF The number of cycles an alternating electric current undergoes per second is known as - ANSWER✔✔Frequency
When the current increases in an AC circuit, what role does inductance play? - ANSWER✔✔reduces current Reactance increases with an increase in - ANSWER✔✔Inductance Which of these items determines the amount of voltage induced in a moving conductor? - ANSWER✔✔Speed of conductor, rate of movement and strength of magnetic field The greatest amount of voltage is induced when the conductor is moving _____ to the magnetic field. - ANSWER✔✔perpendicular What is the frequency of a waveform that occurs 500 times in 10 seconds? (500/10) - ANSWER✔✔50Hz Given frequencies of 60Hz and 50Hz, which has the shortest period? - ANSWER✔✔60Hz (higher the number the shortest period) What is the peak value of a waveform that has a peak-to-peak value of
A coil with many turns of wire will induce less voltage than a coil with fewer turns of wire. - ANSWER✔✔False In an inductor, when the voltage waveform is at 270 degrees, the current waveform will be at _____. - ANSWER✔✔zero How much current will flow in a circuit that is supplied by a 60-Hz, 120volt source and has a 0.03-henry coil? - ANSWER✔✔10.6A If a 15- and a 35-microfarad capacitor are connected in parallel, the total capacitance is _____ microfarads. - ANSWER✔✔ 50 A variable capacitor is used to tune a radio to the desired station. At the low end of the AM band (550kHz), will the capacitive reactance (XC) be higher or lower than it is at the high end of the band (1440kHz)? - ANSWER✔✔Higher
Total opposition to current flow in an AC circuit is called _____. - ANSWER✔✔impedance If the resistance in a series RL circuit is greater than the inductance, the phase angle will be _____. - ANSWER✔✔less than 45 degrees Which of the following statements applies to a parallel RC circuit? - ANSWER✔✔The voltages across the branches are in phase. In a series LC circuit, the capacitor drops 170 volts and the inductor drops 50 volts. The total voltage is _____ volts. - ANSWER✔✔ 120 When resistance is added to an AC circuit containing a capacitor, current will lead voltage by an angle between _____. - ANSWER✔✔zero and 90 degrees
An isolation transformer can help prevent electrical shocks. - ANSWER✔✔True A(n) _____ is often used in fluorescent lighting circuits. - ANSWER✔✔Autotransformer If a sine wave is repeated 10 times per half second, its frequency is - ANSWER✔✔20Hz to compare the phase angle between two wave both waves must have the same - ANSWER✔✔frequency one device that requires sawtooth waveform is - ANSWER✔✔oscilloscope what is the voltage (E) in purely resistive circuit with a current draw of 22A and 10 omega resistance? - ANSWER✔✔220V
which of the following coils is likely to show highest inductance? - ANSWER✔✔short core, many turns and magnetic core total capacitance of three 10uF capacitors and one 5uF capacitor connected in parallel is - ANSWER✔✔35uF circuit's impedance is represented by the letter - ANSWER✔✔Z True power is the product of resistor current squared and the - ANSWER✔✔resistance apparent power is the product of the source voltage and the - ANSWER✔✔current reactive power - ANSWER✔✔performs no work power factor of a circuit with resistance of 75 omega and impedance of
According to the power triangle, the apparent power is___. - ANSWER✔✔Greater than the true power Which of the following uses electromagnetic induction to transfer electrical energy from one circuit to another? - ANSWER✔✔Transformer What is the step-down turns ratio of a transformer with 200 turns in the primary and 100 turns in the secondary? - ANSWER✔✔2:1 Opening the secondary of a CT under load will cause a dangerous level of___. - ANSWER✔✔induced high voltage
Which of the following is true of the current in a capacitive circuit? - ANSWER✔✔It leads the voltage. In sine wave terminology, the average value is___. - ANSWER✔✔0. x peak value In AC circuits containing only resistance,. - ANSWER✔✔All DC rules and laws apply, including Ohm's law If the area of the plates of a capacitor is increased, the amount of capacitance. - ANSWER✔✔Increases The self-induced voltage across in inductance is equal to the change in___. - ANSWER✔✔Current with respect to time
