# Multiple choice question for engineering

## Set 1

1. Inverters converts

a) dc power to dc power

b) dc power to ac power

c) ac power to ac power

d) ac power to dc power

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2. Line-commutated inverters have

a) AC on the supply side and DC on the load side

b) AC on both supply and load side

c) DC on both supply and load side

d) DC on the supply side and AC on the load side

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3. In a VSI (Voltage source inverter)

a) the internal impedance of the DC source is negligible

b) the internal impedance of the DC source is very very high

c) the internal impedance of the AC source is negligible

d) the IGBTs are fired at 0 degrees.

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4. VSIs using GTOs are turned off by

a) load commutation

b) line commutation

c) applying a negative gate pulse

d) removing the base signal

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5. VSIs using IGBTs are turned off by

a) load commutation

b) line commutation

c) applying a negative gate pulse

d) removing the base signal

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6. __________ based inverters do not require self-commutation.

a) IGBT

b) GTO

c) PMOSFET

d) SCR

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7. Identify the circuit given below.

a) Half wave series inverter

b) Full wave series inverter

c) Half wave bridge inverter

d) Half wave parallel inverter

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8. Single phase half bridge inverters requires

a) two wire ac supply

b) two wire dc supply

c) three wire ac supply

d) three wire dc supply

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9. What is the voltage across the R load when only T1 is conducting?

a) Vs

b) Vs/2

c) 2Vs

d) zero

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10. In a single-phase half wave inverter ________ SCR(s) are/is gated at a time.

a) one

b) two

c) three

d) none of the mentioned

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## Set 2

1. What is the voltage across the R load when only T2 is conducting?

a) Vs

b) Vs/2

c) 2Vs

d) Zero

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2. The voltage in a single phase half wave inverter varies between

a) Vs and 0

b) Vs/2 and 0

c) Vs/2 and –Vs/2

d) Vs and –Vs

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3. Below given is a

a) SCR based inverter

b) MOSFET based inverter

c) IGBT based inverter

d) None of the mentioned

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4. The output of a single-phase half bridge inverter on R load is ideally

a) a sine wave

b) a square wave

c) a triangular wave

d) constant dc

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5. In the below given circuit, T1 is fired at 0,T and so on and T2 at T/2, 3T/2 etc. What is the frequency of the alternating voltage obtained?

a) 50 Hz

b) T Hz

c) 1/T Hz

d) T/2 Hz

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6. In the below circuit, if Vs/2 = 50 V. Find, the rms AC voltage that would be ideally obtained.

a) 50 V

b) 100 V

c) 0.707 x 50 V

d) 0.707 x 100 V

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7. Find the conduction time of the diodes if the SCRs are fired at 0 and T/2 respectively in a single phase half wave inverter with R load.

a) 0

b) T/2

c) 2/T

d) insufficient data

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8. The output current wave of a single-phase full bridge inverter on RL load is

a) a sine wave

b) a square wave

c) a triangular wave

d) constant dc

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9. Single-phase full bridge inverters requires

a) 4 SCRs and 2 diodes

b) 4 SCRs and 4 diodes

c) 2 SCRs and 4 diodes

d) 2 SCRs and 2 diodes

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10. Identify the circuit given below.

a) Full wave series inverter

b) Half wave series inverter

c) Full wave bridge inverter

d) Full wave parallel inverter

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## Set 3

1. The output voltage from a single phase full wave bridge inverter varies from

a) Vs to –Vs

b) Vs to zero

c) Vs/2 to zero

d) –Vs/2 to Vs/2

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2. In a single phase full wave bridge inverter, when the output is Vs or –Vs

a) one SCR and one diode are conducting

b) four SCRs are conducting

c) two SCRs are conducting

d) two diodes are conducting

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3. In the following circuit, the diodes D1 to D4 are used to

a) reduce the switching losses

b) send current back to the dc source when SCRs are off

c) send current back to the load when SCRs are off

d) send current back to the dc source when SCRs are conducting

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4. For a full wave bridge inverter, the output voltage (Vo)

a) Vo = Vs/2 for 0 < t < T/2

b) Vo = Vs for 0 < t <T/2

c) Vo = Vs for T/2< t < T

d) Vo = -Vs for T/2< t < 3T/2

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5. For a half wave bridge inverter, the output voltage

a) Vo = – Vs/2 for 0 < t < T/2

b) Vo = – Vs/2 for T/2< t<T

c) Vo = – Vs for 0 < t < T/2

d) Vo = Vs/2 for T/2< t < T

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6. The fundamental component of output voltage for a half wave bridge inverter is given by

a) (4Vs/π) sinωt

b) (2Vs/π) sinωt

c) (Vs/2π) sinωt

d) (Vs)

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7. The fundamental component of output voltage for a full wave bridge inverter is given by

a) (2Vs/π) sinωt

b) (4Vs/π) sinωt

c) (Vs/2π) sinωt

d) (Vs)

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8. A single phase half bridge inverter has a dc voltage source Vs/2 = 115 V. Find the rms value of the fundamental component of output voltage.

a) 510 V

b) 103.5 V

c) 120 V

d) 96 V

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9. A single phase half bridge inverter has load R = 2 Ω and a dc voltage source Vs/2 = 115 V. Find the rms value of the fundamental load current.

a) 10.25 A

b) 51.7 A

c) 86 A

d) 24.8 A

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10. A single phase half bridge inverter has load R = 2 Ω and a dc voltage source Vs/2 = 115 V. Find the power delivered to the load due to the fundamental component.

a) 536 kW

b) 53.61 kW

c) 5.361 kW

d) 536 W

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^{2}x R = 5361.5 Watts.

## Set 4

1. A single phase full bridge inverter has a dc voltage source Vs = 230 V. Find the rms value of the fundamental component of output voltage.

a) 90 V

b) 207 V

c) 350 V

d) 196 V

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2. A single phase full bridge inverter has load R = 2 Ω, and dc voltage source Vs = 230 V. Find the rms value of the fundamental load current.

a) 96 A

b) 0 A

c) 103 A

d) none of the mentioned

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3. A certain full bridge type inverter circuit has its rms value of fundamental load current component given by W. The fundamental frequency component of the load current would be given by

a) W sin ωt

b) (W/√2) sin ωt

c) √2 W sin ωt

d) sin ωt

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4. In a half wave bridge inverter circuit, the power delivered to the load by each source is given by

a) Vs x Is

b) (Vs x Is)/2

c) 2(Vs x Is)

d) None of the mentioned

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5. In a half wave circuit, forced commutation is essential when the

a) load is inductive

b) load is resistive

c) source voltage is below 150 V

d) none of the mentioned

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6. A single phase full bridge inverter circuit, has load R = 2 Ω and dc source Vs = 230 V. Find the value of power delivered to the load in watts only due to the fundamental component of the load current.

a) 5361.5 W

b) 2142.5 W

c) 21424.5 W

d) 214.2 W

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^{2}x R = 21424.5 W.

7. A single phase full bridge inverter is fed from a dc source such that the fundamental component of output voltage = 230 V. Find the rms value of SCR and diode current respectively, for a R load of 2 Ω.

a) 115 A, 80 A

b) 81.33 A, 36.2 A

c) 36.2 A, 0 A

d) 81.33 A, 0 A

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8. For a full bridge inverter with the following load: R = 2 Ω, X_{L} = 8 Ω and X_{C} = 6 Ω.

a) The output voltage lags the current by 45°

b) The output current lags the voltage by 45°

c) The output current lags the voltage by 90°

d) The output current lags the voltage by more than 90°

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^{-1}(X

_{L}– X

_{C})/R = tan

^{-1}(1) = 45°.

9. A single phase full bridge inverter has RLC load. The dc input voltage is 230 V and the output frequency is 50 Hz. Find the expression for the load voltage up to the fifth harmonic.

a) 292 sin 314t + 97.62 sin 314t + 58.57 sin 318t + 28.31 sin 318t + 3.686 sin 318t

b) 292 sin 314t + 97.62 sin (3 x 314t) + 58.57 sin (5 x 318t)

c) 292 sin 314t + 97.62 sin (2 x 314t) + 58.57 sin (3 x 318t) + 28.31 sin (4 x 318t) + 3.686 sin (5 x 318t)

d) 292 sin 512t + 25.62 sin 249t + 6.74 sin 508t

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10. A single phase full bridge inverter has RLC load with R = 4 Ω, L = 35 mH and C = 155 μF. The dc input voltage is 230 V and the output frequency is 50 Hz. Find the rms value of the fundamental load current.

a) 28.31 A

b) 20.02 A

c) 16.69 A

d) 26.90 A

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_{L}= 2 x 3.14 x 50 x 0.035 = 10.99 Ω X

_{C}= 1/(2 x 3.14 x 50 x 155 x 10

^{-6}) = 20.54 Ω Z = 10.345 Ω I = V/Z = 28.31 I(rms) = V/Z√2 = (292.85)/(1.414 x 10.345) = 20.02 A.

## Set 5

1. If a step up chopper’s switch is always kept off then (ideally)

a) Vo = 0

b) Vo = ∞

c) Vo = Vs

d) Vo > Vs

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2. If a step up chopper’s switch is always kept open then (ideally)

a) Vo = 0

b) Vo = ∞

c) Vo = Vs

d) Vo > Vs

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3. Find the average value of output voltage of a basic step-down chopper, with duty cycle = α and load = R Ω.

a) I = Vs x α

b) I = (Vs x α)/R

c) I = 0

d) I = Vs/R

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4. For the below given circuit, find the output current at the instant of commutation.

a) Vo/R

b) Vs/R

c) 0

d) α/2

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_{on}. Therefore, output current at the instant of commutation is Vs/R.

5. For a step-down chopper, find the rms value of output voltage. Let α be the duty cycle and Vs be the input voltage.

a) α x Vs

b) Vs/α

c) √α x Vs

d) Vs/2

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^{on}/T).Vs

^{2}]

^{1/2}= √α x Vs.

6. A step down chopper is operated at 240V at duty cycle of 75%. Find the value of RMS switch (IGBT/MOSFET) current. Take R = 10 Ω.

a) 2.07 A

b) 200 mA

c) 1.58 A

d) 2.4 A

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7. Find the expression for effective input resistance of a step down chopper. With R load and duty cycle = α.

a) R x α

b) R/2

c) 0

d) R/α

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8. A step-up chopper has input voltage of 220 V and output voltage of 660 V. If the conducting time of the IGBT based chopper is 100 μs, compute Toff width of the output voltage pulse.

a) 100 μs

b) 150 μs

c) 50 μs

d) Insufficient data

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9. For a step-up chopper, when the duty cycle is increased the average value of the output voltage

a) increases

b) decreases

c) remains the same

d) none of the mentioned

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10. For a step-down chopper, when the duty cycle is increased the average value of the output voltage

a) increases

b) decreases

c) remains the same

d) none of the mentioned