Review Exam: ELEC02 :AC Flashcards
What is the main reason that alternating current replaced direct current for general use?
AC voltage may be conveniently transformed.
The rmsvalue of an ac current is:
That steady current that produces the same rate of heating in a resistor as the actual current.
An inductor and a resistor are in series with a sinusoidal voltage source. The frequency is set so that the inductive reactance is equal to the resistance. If the frequency is increased, then:
V_L>V_R
To decrease the phase angle below 45°, the following condition must exist:
R>Xc
In residential house wiring the hot wire is usually color coded
black or red
Capacitive reactance, Xc:
Applies only to sine waves.
In a sinusoidally driven series RLC circuit, the inductive reactance is X_L = 200 ohm, the capacitive reactance is Xc= 100 ohm, and the resistance is R = 50 ohm. The current and applied emf would be in phase if:
The capacitance is halved, with no other changes.
In an RLC series circuit, which is connected to a source of emf E_m cos(wt), the current lags the voltage by 45° if:
R= wL-1/wC
w=omega
For a sine wave, one-half cycle is often called a/an ______ .
alternation
When the frequency is increased, the impedance of a parallel RL circuit ______.
increases
Determine the power factor angle in the series circuit which consists of R = 25 ohms, L = 0.2 H across a power supply of 200 volts, 30 Hz?
56.4°
A series circuit composed of a 0.2 H inductor and a 74-µF capacitor is connected to a 60 V variable frequency source. At what frequency will the current be 4 amperes with a lagging power factor?
48 Hz
A load of 20 + j35 ohms is connected across a 220 volts source. Determine the power factor and the VARS.
49.6%, 1042 VARS
A 5O-microfarad is connected in series with a coil having 50 ohms resistance and 150 mH inductance. The source voltage is 100 sin (wt- 30°) V. What is the maximum power?
199W
A series RC circuits is connected to an emf source having angular frequency w. The current:
leads the source emf by an tan^-1 (1/wCR)
When the frequency of the voltage applied to a series RC is increased, the impedance _______
decreases
What is the unit of the power factor?
None of the choices
In a purely capacitive circuit, the current:
Leads the voltage by one fourth of a cycle.
ELI
A coil ol 25.0 µHand capacitor of 100 pF are connected in series. The frequency is 5.00 MHz. What is the impedance vector, R + jX?
0 + j467
A series circuit composed of 100-ohm resistor and a 20- microfarad capacitor connected across a 240 V, 60 Hz line. Which of the following answers is WRONG?
The resulting current is 0.732 ampere.
When the frequency of the voltage applied to a series RC circuit is decreased, the phase angle
increases
A capacitance is connected to a 115 V, 25 Hz mains and takes 5 A. What current will it take when the capacitance
20A
In a sinusoidally driven series RLC circuit the current lags the applied emf. The rate at which energy is dissipated in the resistor can be increased by:
Decreasing the capacitance and making no other changes.
In a purely inductive circuit, the current lags the voltage by:
One-fourth of a cycle.
Determine the phase angle in the series circuit which consistsof R = 25 ohms, L = 0.2 H across a power supply of
200 volts, 30 Hz?
56.4°
