# Multiple choice question for engineering

## Set 1

1. For the below given circuit,

a) T2 and T3 are gated together

b) T1 and T4 are gated together

c) T1 and T3 are gated together

d) T1 and T2 are gated together

### View Answer

2. With respect to the below given circuit, from ωt = 0 to α, ____ thyristor(s) block the forward voltage

a) T1 and T2

b) T2

c) T3 and T4

d) T4

### View Answer

3. With respect to the below given circuit, from ωt = 0 to α,

a) voltage across all the thyristors is zero

b) negative voltage appears across T1 and T2

c) load voltage is Vm/2

d) voltage across T3 and T4 is zero

### View Answer

4. For the below given circuit, when the devices T1 and T2 are conducting from ωt = α till they are naturally commutated at π voltage across the other two pair of devices is

a) zero

b) positive (forward voltage)

c) negative (reverse voltage)

d) none of the mentioned

### View Answer

5. A single-phase full converter B-2 type connection has a RLE type of motor load connected. The minimum requirement to turn-on the device is

a) α > 30°

b) Vm sinα > E

c) Vm sinα < E

d) α < 30°

### View Answer

6. For the below shown circuit with continuous load current.

Each thyristor pair conducts for

a) π radians

b) 2π radians

c) < π radians

d) > π radians

### View Answer

7. For the below given circuit

a) all the devices are gated together

b) T3 and T4 are gated together

c) T3 and T1 are gated together

d) T3 and T2 are gated together

### View Answer

8. For the below shown circuit has dis-continuous load current waveform.

Each thyristor pair conducts for

a) π radians

b) 2π radians

c) < π radians

d) > π radians

### View Answer

9. A single-phase full converter with B-2 type of connection has a continuous load current waveform. The thyristor pairs T3, T4 is triggered at ωt =

a) 0

b) α

c) π+α

d) π-α

### View Answer

10. The PIV for each diode in a single-phase, full converter with B-2 type of controlled rectifier is

Consider supply voltage as Vs = Vm sinωt.

a) 2Vm

b) Vm

c) Vm/2

d) Vm/√2

### View Answer

## Set 2

1. A single-phase half-wave rectifier with a FD is supplied by Vs = 240 V, 50 Hz, AC source with a load R = 10 Ω, L = 0.8 mH. The firing angle is so adjusted such that the output voltage obtained is 100 V. Find the firing angle.

a) 62°

b) 102°

c) 31°

d) 47°

### View Answer

2. For the below shown circuit, a motor load (RLE) is connected to the SCR through supply Vs. The minimum value of the firing angle to turn on the SCR would be

a) Sin^{-1}(E/Vm)

b) Sin^{-1}(Vm/E)

c) Cos^{-1}(E/Vm)

d) Cos^{-1}(E/Vm)

### View Answer

^{-1}(E/Vm).

3. Choose the correct statement with respect to the below given circuit.

a) The load current can never be zero

b) The source current can never be zero

c) The load voltage can never be zero

d) All the given statements are false

### View Answer

4. By using a freewheeling diode (FD) in a rectifier with RL load, the power consumed by the load

a) increases

b) decreases

c) is not affected

d) decreases to zero

### View Answer

5. A 230 V, 50 Hz, one-pulse SCR controlled converter has extinction angle β = 210°. Find the circuit turn-off time

a) 10 m-sec

b) 0

c) 8.3 m-sec

d) 5.4 m-sec

### View Answer

6. A 230V, 50Hz, single-pulse SCR is feeding a RL load with α = 40° and β = 210°. Find the value of average output voltage

a) 54 V

b) 106 V

c) 84 V

d) 32 V

### View Answer

7. A single-pulse transformer with secondary voltage of 230 V, 50 Hz, delivers power to bulb of R = 10 Ω through a half-wave controlled rectifier circuit. For α = 60°, find the average current in the bulb

a) 2.5 A

b) 7.7 A

c) 9.6 A

d) 3 A

### View Answer

8. A single-pulse transformer with secondary voltage of 230 V, 50 Hz, delivers power to bulb of R = 10 Ω through a half-wave controlled rectifier circuit. For α = 60° and output AC power of 2127 Watts, find the rectification efficiency

a) 98.6 %

b) 42 %

c) 28 %

d) 19 %

### View Answer

^{2}xR = 602.8 W Rectification efficiency = Pdc/Pac = 28.32 %.

9. Find the PIV of the SCR

a) Vs

b) 2Vs

c) √2Vs

d) Vs/2

### View Answer

10. An SCR rectifier circuit is designed such that the average output voltage is 77.64 V & RMS value of output voltage is 145.873 V. Find the voltage ripple factor.

a) 1.879

b) 0.532

c) 1.590

d) 0.629

### View Answer

^{2}-1) = 1.5908.

## Set 3

1. For the following RC triggering circuit with R load and a firing angle of α, the voltage across the R load is zero for

a) ωt = 0 to α and ωt = π to 2π+α

b) ωt = 0 to α

c) ωt = π to 2π+α

d) ωt = α to 2π

### View Answer

2. For the following circuit, the SCR (thy2) is

a) forced commutated at ωt = π

b) forced commutated at ωt = 2π

c) naturally commutated at ωt = π

d) naturally commutated at ωt = 2π

### View Answer

3. For the following RC triggering circuit with R load and a firing angle of α, the voltage across the SCR (thy2) will be zero for

a) ωt = 0 to α & ωt = π to 2π+α

b) ωt = 0 to π

c) ωt = α to 2π

d) ωt = α to π

### View Answer

4. In case of an RC full wave firing circuit with R load, the voltage across the load is zero for____________

a) ωt = 0 to α and ωt = π to 2π+α

b) ωt = 0 to α

c) ωt = π to 2π+α

d) ωt = α to 2π

### View Answer

5. For an RC full wave firing circuit the empirical formula for calculating the value of RC is

a) RC = 157/ω

b) RC = 157 x ω

c) RC = ω/157

d) RC = 157 x ω^{2}

### View Answer

6. Pulse triggering can be only used by the _____________ type of triggering circuit

a) R

b) RC

c) UJT

d) RLC

### View Answer

7. The UJT terminals are

a) E, B1 and B2

b) E1, E2 and B

c) E, G and C

d) G, S and D

### View Answer

8. In case of the UJT firing circuit, when the UJT turns on

a) the capacitor starts to charge

b) the capacitor starts to discharge

c) the capacitor remains unaffected

d) there is no capacitor in a UJT firing circuit

### View Answer

9. In the UJT firing circuit, the pulses are generated while the

a) capacitor charges

b) capacitor discharges

c) capacitor voltage is zero

d) there is no capacitor in a UJT firing circuit

### View Answer

10. Find the value of the charging resistor in case of a UJT firing circuit with firing frequency of 2 kHz, C = 0.04 μF, η = 0.72

a) 5.62 kΩ

b) 37 kΩ

c) 4.23 kΩ

d) 9.82 kΩ

### View Answer

## Set 4

1. The below shown single phase controlled rectifier configuration is a

a) two pulse M-2 Connection

b) two pulse B-2 Connection

c) single pulse M-2 Connection

d) single pulse B-2 Connection

### View Answer

2. In the below shown circuit, considering the load to be purely R load, the thyristor T2 would conduct from ωt =

a) 0 to π

b) α to π

c) π+α to 2π

d) π to 2π+α

### View Answer

3. For a single pulse M-2 rectifier with RL load and firing angle α >0°, the value of the inductance L is such that the load current is continuous.

Choose the correct statement.

a) The load current can never be positive

b) The load current can never be negative

c) The load current can never be zero

d) The load current is a constant DC

### View Answer

4. For the circuit below, the transformer ratio is 1:1 and Vs = Vm sinωt. When T1 is forward biased and is triggered at α than T2 is

a) subjected to a forward voltage of Vm sinα

b) subjected to a forward voltage of 2Vm sinα

c) subjected to a reverse voltage of Vm sinα

d) subjected to a reverse voltage of 2Vm sinα

### View Answer

5. The circuit turn-off time of M-2 type connection is

a) π/ω

b) α/ω

c) π-α/ω

d) π+α/ω

### View Answer

6. Find the expression for the average value of the output voltage for the below given circuit. Consider the load current to be continuous, firing angle = α, transformer ration 1:1 and Vs = Vm sinωt.

a) (Vm/π)cosα

b) (Vm/π)(1+cosα)

c) (2Vm/π)cosα

d) (2Vm/π)(1+cosα)

### View Answer

7. A fully controlled converter uses

a) diodes only

b) thyristors only

c) both diodes and thyristors

d) none of the mentioned

### View Answer

8. A single phase full-converter using R load is a _________ quadrant converter and that using an RL load without FD is a __________ quadrant converter

a) one, one

b) two, one

c) one, two

d) two, two

### View Answer

9. A single phase full controlled bridge converter (B-2) uses

a) 4 SCRs and 2 diodes

b) 4 SCRs

c) 6 SCRs

d) 4 SCRs and 2 diodes

### View Answer

10. In a B-2 type full controlled bridge converter

a) one SCR conducts at a time

b) two SCRs conduct at a time

c) three SCRs conduct at a time

d) four SCRs conduct at a time

### View Answer

## Set 5

1. A voltage source Vs = Vm sinωt is connected in series with a resistance R and an SCR. At some firing angle delay of α a positive gate pulse is applied to the SCR which turns on the SCR. Considering ideal conditions, at the instant α the voltage at the resistor terminals Vo

a) falls to zero

b) falls to –Vm sin α

c) rises to Vm sin α

d) rises to Vm sin ωt

### View Answer

2. The average output voltage is maximum when SCR is triggered at ωt =

a) π

b) 0

c) π/2

d) π/4

### View Answer

3. In the below given circuit, the SCR is triggered at a certain firing angle α.

The load current falls to zero at ωt =

a) α

b) α/2

c) π

d) π/2

### View Answer

4. In the method of phase control, the phase relationship between ___ & ___ is controlled by varying the firing angle

a) supply current, supply voltage

b) end of the load current, end of the load voltage

c) start of the load current, start of the load voltage

d) load current, load voltage

### View Answer

5. In a single phase half-wave thyristor circuit with R load & Vs=Vm sinωt, the maximum value of the load current can be given by

a) 2Vm/R

b) Vs/R

c) Vm/2

d) Vs/2

### View Answer

6. Below shown ideal circuit is triggered at a firing angle of α. The voltage across the SCR is zero from ωt =

a) 0 to α

b) 0 to π

c) α to 2π

d) α to π

### View Answer

7. Below shown ideal circuit is triggered at a firing angle of α. From ωt = π to 2π+α

a) SCR voltage is zero

b) Load voltage is maximum

c) SCR voltage is –Vmsinα

d) SCR acts like a short circuit

### View Answer

8. For a single phase thyristor circuit with R load & firing angle α, the conduction angle can be given by

a) π+α

b) 2π+α

c) π-α

d) α

### View Answer

9. For the below given circuit with firing angle α & angular frequency of ω, the circuit turn-off time in secs can be given by

a) α/π

b) π/α

c) ω/π

d) π/ω

### View Answer

_{off}= π/ω.

10. A single-phase half-wave thyristor circuit with R load is triggered at an angle of α = 0°. As such, the maximum value of the average output voltage would be given by

Consider Vs = Vm sinωt.

a) Vm

b) 2Vm/π

c) Vm/π

d) Vm/α