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Power

 

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. 

 

Power Sample Questions:

 

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.

 

 

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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.

 

 

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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.

 

 

a)           b)

c)           d)

 


Answer: d)

Explanation: Given,

 

 

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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.  

 

 

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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

 


Answer: 

 

Explanation: 

 

 

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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

 

 

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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

Explanation: 

 

 

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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.

 

 

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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.

 

 

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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.

 

 

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