Power electronics deals in the design, development, control and transformation of power in the electrical form of energy. Power electronic system converts electrical energy into electric load through a control circuit. It involves the processing of high voltages and currents to deliver power as an output. The application of power electronics ranges from AC/DC converters, semiconductor devices to inverters.
Question 1: Which of the following is true in case of forward biased p-n junction diodes?
a) The positive terminal of the battery takes electrons from the p-region
b) The positive terminal of the battery injects electrons into the p-region
c) The negative terminal of the battery takes electrons from the p-region
d) None of these
Answer: a) The positive terminal of the battery takes electrons from the p-region
Explanation: Since the diode is forward biased, the positive side is connected to p and vice versa.
Question 2: ___________ are the majority carriers in n-type material.
a) Protons b) Electrons
c) Charges d) None of these
Answer: b) Electrons
Explanation: The n-region has greater concentration of electrons as compared to the p-region in a P-N junction diode.
Question 3: Find the average value of output current for a 1-phase HW diode rectifier with R load, having RMS output current of 200 A.
Question 4: In a three phase diode half wave rectifier using 3 diodes, each diode conducts for _______ degree at a time.
a) 60 b) 120
c) 180 d) 270
Answer: b) 120
Explanation: In a three phase diode half wave rectifier, only one diode conducts at a time.
Question 5: Find the average gate power dissipation when the maximum allowable gate power dissipation is 20 KW, with a duty cycle 50%.
a) 2 KW b) 5 KW
c) 10 KW d) 15 KW
Question 6: The duty cycle can be written in the form of
a) fT b) f/T
c) T/f d) T
Answer: a) fT
Explanation: Given, Pulse on period = T, Periodic time = f
Question 7: Find the triggering frequency when the average gate power dissipation is 0.6 W and the peak gate drive power is 10 Watts. The gate source has a pulse width of 20μsec duration.
a) 1000 Hz b) 2000 Hz
c) 3000 Hz d) 5000 Hz
Answer: c) 3000 Hz
Question 8: A ____________ is used to control the dc voltage to the inverter.
a) Transformer b) Chopper
c) Converter d) All of the above
Answer: b) Chopper
Explanation: External control of dc voltage is obtained by the use of a chopper, which gets further converted from variable dc to variable ac by the converters.
Question 9: Before the invention of semiconductor technology _________ devices were used for the voltage control applications.
a) Induction machine b) Inverters
c) Tap changing transformer d) None of these
Answer: c) Tap changing transformer
Explanation: Tap changing transformer can give variable ac from fixed ac without a change in frequency.
Question 10: ___________ controllers are used in electrical heating applications.
a) DC voltage b) AC voltage
c) Both (a) and (b) d) None of these
Answer: b) AC voltage
Explanation: Variable ac supply is required for electrical heating. The devices are fired to apply enough temperature.