Power Electronics Questions and Answers in Quiz Form 9 for Practice

121. The triac is …………….

1. A four-terminal device
2. Not a thyristor
3. Like a bidirectional SCR
4. Answers (1) and (2)

122. The UJT may be used as ……………….

1. A sawtooth generator
2. A rectifier
3. Am amplifier
4. None of the above

123. The V-I characteristics for a triac in the first and third quadrants are essentially identical to those of ………………. in its first quadrant

1. SCR
2. UJT
3. Transistor
4. none of the above

124. To turn on UJT, the forward bias on the emitter diode should be …………… the peak point voltage

1. Equal to
2. More than
3. Less than
4. None of the above

125. TRIAC is a semiconductor power electronic device which contains

1. Two SCRs connected in parallel
2. Two SCRs connected in series
3. Two SCRs connected in reverse parallel
4. Two BJTs connected in series

126. Under harmonic free load voltages, the 3 phase VSI

1. Does not contains third harmonic
2. Does not contains fifth harmonic
3. Does not contains second harmonic
4. Does not contains seventh harmonic

127. Unipolar modulation is generally used in

1. AC – DC converters
2. DC – AC converters
3. AC – AC converters
4. DC – DC converters

128. Very large values of modulation index (greater than 3.24 lead to)

1. Sine AC output voltage
2. Triangular AC output voltage
3. Square AC output voltage
4. Trapezoidal AC output voltage

129. Voltage commutation circuit can be converted into a current commutation by interchanging the positions of

1. Capacitor and SCR
2. Inductor and capacitor
3. Diode and capacitor
4. Capacitor and load

130. When a UJT is turned ON, the resistance between emitter terminal and lower base terminal …………….

1. Is decreased
2. Is increased
3. Remains the same
4. None of the above

131. When the emitter terminal of a UJT is open, the resistance between the base terminal is generally ………………..

1. Low
2. Extremely low
3. High
4. None of the above

132. When the temperature increases, the inter-base resistance (RBB) of a UJT ………….

1. Decreases
2. Remains the same
3. Increases
4. None of the above

133. When the temperature increases, the intrinsic stand off ratio ……….

1. Decreases
2. Essentially remains the same
3. Increases
4. None of the above

134. Which of the following is not a characteristic of UJT?

1. Negative resistance
2. Peak-point voltage
3. Intrinsic stand off ratio
4. Bilateral conduction

135. With increase in firing angle

1. Harmonic distortion increases and quality of input current decreases
2. Harmonic distortion decreases and quality of input current increases
3. Both harmonic distortion and quality of input current increases
4. Both harmonic distortion and quality of input current decreases