As you may know, voltage alternating current (VAC) is a type of current that changes direction periodically. This means that the voltage level also changes direction periodically. VAC is used in many electrical applications, such as powering motors and lighting.
One of the most important things to know about VAC is that the current and voltage levels are not always in sync. This means that the voltage level may be changing direction while the current level is still going in the same direction. This can lead to problems if the two are not properly synchronized.
That’s why it’s important to know the answers to these VAC questions:
1. What is the main difference between VAC and other types of current?
2. How can VAC cause problems if the current and voltage levels are not properly synchronized?
3. What are some of the most common applications for VAC?
4. What are some of the safety concerns to keep in mind when working with VAC?
Memorizing the answers to these questions will help you better understand VAC and avoid any potential problems.
Voltage Alternating Current MCQ and Answers
1. A sine wave with an RMS value of 12 V is riding on a dc level of 18 V. The maximum value of the resulting waveform is
(A) 6 V
(B) 30 V
(C) 35 V
(D) 0 V
2. A sine wave of 15 kHz is changing at a faster rate than a sine wave with a frequency of
(A) 25 kHz
(B) 12 kHz
(C) 18 kHz
(D) 1.3 MHz
3. A ramp is the type of waveform characterized by a non-linear increase or decrease in voltage or current.
4. Sine wave A has a positive-going zero crossing at 45°. Sine wave B has a positive-going zero crossing at 60°. Which of the following statements is true?
(A) Wave A leads wave B by 15°
(B) Wave A lags wave B by 15°
(C) Wave A leads wave B by 105°
(D) Wave A lags wave B by 105°
5. A sinusoidal current has an rms value of 14 mA. The peak-to-peak value is
(A) 45.12 mA
(B) 16 mA
(C) 39.6 mA
(D) 22.6 mA
6. If the rms current through a 6.8 k? resistor is 8 mA, the rms voltage drop across the resistor is
(A) 5.44 V
(B) 54.4 V
(C) 7.07 V
(D) 8 V
7. If the rms current through a 4.7 k? resistor is 4 mA, the peak voltage drop across the resistor is
(A) 4 V
(B) 18.8 V
(C) 26.6 V
(D) 2.66 V
8. The unit of frequency is the hertz.
9. If a sine wave goes through 10 cycles in 20 ?s, the period is
(A) 20 ?s
(B) 4 ?s
(C) 2 ?s
(D) 100 ?s
10. The conductive loop on the rotor of a simple two-pole, single-phase generator rotates at a rate of 400 rps. The frequency of the induced output voltage is
(A) 40 Hz
(B) 100 Hz
(C) 400 Hz
11. How many degrees are there in ?/3 rad?
12. Amplitude is the maximum value of a voltage or current.
13. A pulse waveform has a high time of 8 ms and a pulse width of 32 ms. The duty cycle is
14. To produce an 800 Hz sine wave, a four-pole generator must be operated at
(A) 200 rps
(B) 400 rps
(C) 800 rps
(D) 1,600 rps
15. If the RMS voltage drop across a 15 k? resistor is 16 V, the peak current through the resistor is
(A) 15 mA
(B) 1.5 mA
(C) 10 mA
(D) 1 mA
16. The angular position of a phasor represents the angle of the sine wave with respect to a reference.
17. One sine wave has a positive-going zero crossing at 15° and another sine wave has a positive-going zero crossing at 55°. The phase angle between the two waveforms is
(D) None of the above
18. The instantaneous value is the voltage or current value of a waveform at its peak.
19. If the peak of a sine wave is 13 V, the peak-to-peak value is
(A) 6.5 V
(B) 13 V
(C) 26 V
(D) None of the above
20. The duty cycle of a pulse waveform with a pulse width of 10 µs and a period of 100 µs is 25%.
21. When a sine wave has a frequency of 100 Hz in 12 s it goes through
(A) 1/100 cycle
(B) 12 cycles
(C) 120 cycles
(D) 1,200 cycles
22. Periodic is characterized by a repetition at fixed time intervals.
23. The designation rms means repetitions measured per second.
24. A 20 kHz pulse waveform consists of pulses that are 15 ?s wide. The duty cycle
(A) Is 1%
(B) Is 30%
(C) Is 100%
(D) Cannot be determined
25. A square wave has a period of 60 ?s. The first odd harmonic is
(A) 5 kHz
(B) 50 kHz
(C) 500 kHz
(D) 33.33 kHz
26. The average value of a 12 V peak sine wave over one complete cycle is
(A) 0 V
(B) 1.27 V
(C) 7.64 V
(D) 6.37 V
27. Two series resistors are connected to an ac source. If there are 7.5 V rms across one resistor and 4.2 V rms across the other, the peak source voltage is
(A) 16.54 V
(B) 1.65 V
(C) 10.60 V
(D) 5.93 V
28. A sine wave with a period of 4 ms is changing at a faster rate than a sine wave with a period of
(A) 0.0045 s
(B) 2 ms
(C) 1.5 ms
(D) 3,000 ?s
29. A signal with a 400 ?s period has a frequency of
(A) 250 Hz
(B) 2,500 Hz
(C) 25,000 Hz
(D) 400 Hz
30. A waveform has a baseline of 3 V, a duty cycle of 20%, and an amplitude of 8 V. The average voltage value is
(A) 4 V
(B) 4.6 V
(C) 1.6 V
(D) 11 V
31. A saw-tooth wave has a period of 10 ms. Its frequency is
(A) 10 Hz
(B) 50 Hz
(C) 100 Hz
(D) 1,000 Hz
32. Average value of a sine wave is 0.707 times the peak value.
33. A phasor represents
(A) The magnitude and a quantity direction
(B) The width of a quantity
(C) The phase angle
(D) The magnitude of a quantity
34. The length of a phasor represents the amplitude.
35. The average half-cycle value of a sine wave with a 40 V peak is
(A) 25.48 V
(B) 6.37 V
(C) 14.14 V
(D) 50.96 V
36. A 1 kHz signal has a period of 1 ms.
37. Duty cycle is the characteristic of a pulse waveform that indicates the high time versus the low time.
If you’re like most people, you probably have a lot of questions about voltage and alternating current (AC). Here are some of the most frequently asked questions about AC voltage.
FAQs on Voltage Alternating Current
What is AC voltage?
AC voltage is an electric potential difference that reverses direction periodically. The standard unit of AC voltage is the volt (V). AC voltage is used to power many devices and appliances in our homes, including lights, TVs, and computers.
How does AC voltage work?
AC voltage is generated by an AC power source, such as a generator or an electric utility. The AC power source provides a sinusoidal voltage wave that alternates between positive and negative values. The amplitude of the wave (measured in volts) determines the amount of power that is delivered to the load. The frequency of the wave (measured in hertz) determines the rate at which the voltage alternates.
What are the benefits of AC voltage?
AC voltage has a number of advantages over direct current (DC) voltage. First, AC voltage can be easily transformed into different voltages using a transformer. This ability to change voltages is important because it allows electricity to be delivered efficiently over long distances. Second, AC voltage can be easily controlled using devices such as switches, relays, and contactors. Finally, AC voltage is less likely than DC voltage to cause harmful electrical shocks.
Are there any disadvantages of AC voltage?
AC voltage does have some disadvantages. First, AC voltage is more complex than DC voltage and requires more careful handling. Second, AC voltage can cause electrical interference that can disrupt electronic equipment.