Alternating Current and Voltage Online Test – Multiple Choice Questions and Answers 1. Most practical alternators generate electricity from a permanent magnet rotating within a varying electromagnetic field a coil rotating within a magnetic field a magnetic field rotating around fixed windings none of the above 2. A single-phase induction motor operates at a fixed speed is less reliable than a three-phase synchronous motor is self-starting none of these 3. What is the fourth harmonic of a fundamental frequency of 400 Hz? 1.6 kHz 4 Hz 4 kHz 100 Hz 4. A half-cycle average voltage of 12 V is equal to what rms voltage? 8.48 V 7.64 V 18.84 V 13.33 V 5. A rectangular wave that has a duty cycle of 50% could be called a triangular wave square wave sawtooth wave “c” wave 6. What is the average voltage when a rectangular wave’s base line voltage is 20 V, its peak-to-peak voltage is 50 V, and its duty cycle is 20%? 26 V 30 V 40 V 45 V 7. In both induction and synchronous ac motors the operating speed is very steady the stator magnetic field rotates the “squirrel cage” forms the rotor the stator magnetic field is stationary 8. A pulse waveform has a high time of 8 ms and a pulse width of 32 ms. The duty cycle is 1% 25% 50% 100% 9. The effective value of a sine wave is equal to 0.636 of peak voltage 0.707 of peak voltage sin 45° of peak voltage both 0.707 of peak voltage and sin 45° of peak voltage 10. What is the instantaneous peak voltage at 250° on a 6 V peak sine wave? +5.64 V –26.13 V –5.64 V +26.13 V Loading … Question 1 of 10
