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Multiple choice question for engineering

Set 1

1. The below given circuit can
tough-power-electronics-questions-answers-q1
a) operate in all the four quadrants
b) operate in only the first and second quadrant
c) operate in only the fourth and third quadrant
d) operate in only the first and fourth quadrant

View Answer

Answer: b [Reason:] For operation in the third and the fourth quadrant, the polarity of the load emf E should be reversed.

2. In the below shown chopper circuit, when CH3 is on
tough-power-electronics-questions-answers-q1
a) both load voltage and current are zero
b) both load voltage and current are positive
c) both load voltage and current are negative
d) none of the mentioned

View Answer

Answer: c [Reason:] When CH3 is switched on, IIIrd quadrant operation is obtained in which both load current and load voltage are negative. D2-CH3-Vs.

3. In the below given type E chopper circuit, when CH3 and CH2 are switched on and then CH3 is switched off after some time, then
tough-power-electronics-questions-answers-q1
a) load current falls to zero
b) negative current freewheels through CH2, D4
c) positive current freewheels through CH2, D4
d) none of the mentioned

View Answer

Answer: b [Reason:] When CH3 is first on then, load gets connected to Vs and charges the inductor L. When it CH3 switched off, current has to flows through through the same direction (negative) because of the L. Current starts to freewheel from CH2 and D4.

4. For the type E chopper to be operated in the fourth quadrant
a) only one switch is operated
b) two switches are operated
c) three switches are operated
d) all the switches are operated

View Answer

Answer: a [Reason:] For IVth quadrant, only CH4 is operated. The difference between “operated” and “on” should be noted. Operated means it can is literally operated i.e. it is switched on and off and on and off, whereas on means it is on continuously.

5. For the fourth quadrant operation, the current flows through
tough-power-electronics-questions-answers-q1
a) CH1, D2, L and D1
b) CH4, D3, L and D4
c) CH4, D2, L and E
d) CH1, D2, L and D3

View Answer

Answer: c [Reason:] With CH4 on in the fourth quadrant, positive current flows through CH4, D2, L and E.

6. When CH4 is turned on and then off
tough-power-electronics-questions-answers-q1
a) load current falls to zero
b) negative current freewheels through D2, D3
c) positive current freewheels through D2, D3
d) none of the mentioned

View Answer

Answer: c [Reason:] When CH4 is on, positive current flows through CH4, D2, L and E. When CH4 is opened, current is fed back to the source from D2, D3.

7. Find the expression for the ripple factor in terms of duty cycle α for a type A step down chopper
a) √(1-α/α)
b) α2/2
c) √α/2
d) √(1-α)

View Answer

Answer: a [Reason:] RF = Vr/Vo Vr = √α x Vs = √(αVs2 – α2Vs2) = Vs √(α- α2) RF = Vs.√(α- α2)/Vs.α = √(1-α/α).

8. The AC ripple voltage is given by
a) Vrms/Vo
b) Vrms2
c) √(Vrms2 – Vo2)
d) √(Vrms + Vo)

View Answer

Answer: c [Reason:] The term AC ripple voltage is used for knowing the harmonic content of a waveform, without calculating its harmonic components. It is the rms difference of ac and dc voltage.

9. The expression for the thyristor (chopper switch) current is given by
I = (α2.Vs – αE)/R
Find the value of firing angle α, for which the thyristor current is maximum.
a) 2Vs/π
b) 180°
c) E/2Vs
d) Vs/R

View Answer

Answer: c [Reason:] In the given expression, to find the maximum value of α dI/dα = 0 Therefore, dI/dα = (2αVs – E)/R = 0 α = E/2Vs.

10. In a type E chopper, if all the four chopper switches are closed simultaneously then
a) load is short circuited
b) supply is short circuited
c) both load and supply are shorted
d) none of the mentioned.

View Answer

Answer: b Expression: Before anything, the supply will be shorted by CH1 and CH2 first.

11. A type A step down chopper has Vs = 220 V and is connected to RLE load. With R = 1 Ω, E = 24 V and L large enough to maintain continuous conduction. Find the average value of load current for a duty cycle of 30 %.
a) 100 A
b) 22 A
c) 42 A
d) 16.5 A

View Answer

Answer: c [Reason:] I = (αVs – E)/R = 42 A.

12. A step down chopper has Vs = 220 V and is connected to RLE load. With R = 1 Ω, E = 24 V and L = 5 mH. The chopping period is 2000 μs and the on-period is 600 μs. Find the value of minimum steady state output current.
a) 33 A
b) 42 A
c) 0 A
d) 51 A

View Answer

Answer: d [Reason:] I(min) = (Vs/R) x [ (1 – e-m)/(1 – e-n) ] – (E/R) m = Ton / (L/R) = R.Ton/L = 0.12 n = T/(L/R) = R.T/L T = 2000μs n = 0.4 I (min) = (220/1) x [ (1 – e-0.12)/(1 – e-0.4) ] – (24/1) = 51.46 A.

Set 2

1. In the figure shown below, the capacitor C is used to
tricky-power-electronics-questions-answers-q1-q2-q4
a) maintain the load voltage constant
b) protect the load
c) protect the chopper switch (SW)
d) maintain the load current constant

View Answer

Answer: a [Reason:] It is a step-up/step-down chopper, the C maintains the load voltage constant.

2. In the below shown step-up/step-down chopper circuit, when the switch (SW) is on
q4.png”>tricky-power-electronics-questions-answers-q1-q2-q4
a) current through inductor rises and the load voltage is zero
b) current through inductor rises and the load voltage is Vs
c) current through inductor decays and the load voltage is zero
d) current through inductor decays and the load voltage is Vs

View Answer

Answer: b [Reason:] During Ton, current flows from Vs-CH-L-Vs. Current through L rises from I1 to I2 and Vs appears across the inductor and load as they are in parallel. Voltage drop at the diode has to be considered as zero.

3. For a step-up/step-down chopper, if α (duty cycle) < 0.5 then
a) Vo = Vs
b) Vo < Vs
c) Vo > Vs
d) none of the mentioned

View Answer

Answer: b [Reason:] Vo = Vs (α/1-α) For duty cycle is less than 0.5, the circuit behaves like a step down chopper. Hence, Vo < Vs.

4. In the below shown step-up/step-down chopper circuit, when the chopper switch (SW) if first on and then off, then the current flows from path
q4.png”>tricky-power-electronics-questions-answers-q1-q2-q4
a) Vs-CH-L-Vs
b) L-Load-D-L
c) L-D-Load-L
d) no current flows

View Answer

Answer: b [Reason:] When the chopper switch is off, polarity of emf induced in the inductor L gets reversed biased. Emf induced in L forward biases the diode D and L starts to discharge from inductor-load-diode-inductor.

5. For a step-up/step-down chopper, if current increases from I1 to I2 linearly during Ton, then find the energy stored in the inductor during Ton
a) zero
b) Vs x (I1 + I2)
c) Vs x [ (I1 + I2)/2 ] x Ton
d) Vs x [ (I1 + I2)/2 ] x T

View Answer

Answer: c [Reason:] Iavg = [ (I1 + I2)/2 ] Energy stored = Win = Vs x [ (I1 + I2)/2 ] x Ton.

6. A step-down chopper is also called as a
a) first-quadrant chopper
b) second-quadrant chopper
c) third-quadrant chopper
d) fourth-quadrant chopper

View Answer

Answer: a [Reason:] It is called as a first quadrant chopper as the current always flows from source to load and the current and voltage both are always positive.

7. For the type-B chopper shown below
tricky-power-electronics-questions-answers-q7-q8-q9
a) during Ton, Vo = 0 and L stores energy
b) during Ton, Vo is not 0 and L stores energy
c) during Ton, Vo = 0 and L releases energy
d) during Ton, Vo is not 0 and L releases energy

View Answer

Answer: a [Reason:] During Ton, SW is on and vo = 0 as the switch S.C’s the load. E drives current through L and charges it.

8. For the type-B chopper shown below
tricky-power-electronics-questions-answers-q7-q8-q9
a) during Toff, Vo = (E + Ldi/dt) and D is conducting
b) during Toff, Vo = (E + Ldi/dt) and D is not-conducting
c) during Toff, Vo = 0
d) during Toff, Vo = Vs

View Answer

Answer: a [Reason:] When switch Is off, Vo = E + Ldi/dt exceeds source voltage Vs and D (diode) is forward biased and begins to conduct.

9. The below given chopper is that of a
tricky-power-electronics-questions-answers-q7-q8-q9
a) step-up chopper
b) step-down chopper
c) step-up/step-down chopper
d) depends on the duty cycle

View Answer

Answer: a [Reason:] The load voltage Vo = E + L(di/dt) is greater than Vs, hence it is a step-up chopper.

10. The type-C chopper or two quadrant type-A chopper has
a) type-A and type-B choppers in series
b) type-A and type-B choppers in parallel
c) two type-A choppers in series
d) two type-A choppers in parallel

View Answer

Answer: b [Reason:] The type-C chopper is a two quadrant chopper, it operates in the 1st and the 2nd quadrant. It has type-A and type-B choppers connected in parallel.

Set 3

1. In which year was the first automobile built?
a) 1759
b) 1769
c) 1785
d) 1790

View Answer

Answer: b [Reason:] French engineer Nicholas Cugnot built the first road vehicle propelled by its own power.

2. Onesiphare Pacqueur invented which one of these?
a) Gear box
b) Steering wheel
c) Differential
d) IC Engine

View Answer

Answer: c [Reason:] Onesiphare Pacqueur of France invented the first differential.

3. Trucks and Buses use which type of fuel?
a) Petrol
b) LPG
c) CNG
d) Diesel

View Answer

Answer: d [Reason:] Diesel fuel is used in heavy vehicles like trucks and buses.

4. A 4*2 drive vehicle implies that
a) It has 4*2=8 wheels
b) It has 2 auxiliary wheels and 4 drive wheels
c) It has 4 wheels out of which 2 are drive wheels
d) None of the mentioned

View Answer

Answer: c [Reason:] If mentioned as a*b drive, ‘a’ represents number of wheels and ‘b’ represents number of drive wheels.

5. A conventional suspension system uses which of these
a) Leaf Springs
b) Coil Springs
c) Torsion bars
d) None of the mentioned

View Answer

Answer: a [Reason:] Leaf Spring is used in conventional suspension systems.

6. Sir Rudolf Diesel invented diesel engine in which year?
a) 1905
b) 1916
c) 1920
d) 1913

View Answer

Answer: d [Reason:] Diesel engine was invented by Rudolf Diesel in 1913.

7. Hindustan Motors Limited, Calcutta was setup in which year
a) 1950
b) 1945
c) 1943
d) 1942

View Answer

Answer: c [Reason:] In 1943 and 1944 two automobile companies namely, Hindustan Motors Limited, Calcutta and Premier Automobiles Limited, Bombay were setup in india.

8. Ford started production of his model ‘T’ car with an initial run of how many vehicles
a) 15000
b) 6000
c) 2000
d) 20000

View Answer

Answer: d [Reason:] Model’T’ cars were the first assembly line produced cars and started with an initial run of 20000 units.

9. In 1832 who patented first 3-speed Transmission
a) W.H.James
b) Rudolf Diesel
c) Richard Trevithick
d) William Ford

View Answer

Answer: a [Reason:] W.H.James patented the first 3-speed Transmission in England.

10. First car arrived in India in which year
a) 1890
b) 1893
c) 1897
d) 1901

View Answer

Answer: c [Reason:] In 1897 first car arrived in india.

Set 4

1. A 150 c.c. two-stroke petrol engine running at 5000 rpm can develop a maximum brake power of
a) 15 kW
b) 10 kW
c) 5 kW
d) 1 kW

View Answer

Answer: c [Reason:] These type of engines can develop a maximum brake power of 5 kW.

2. In Wankel engines, how many power strokes occur per rotor revolution
a) 1
b) 2
c) 3
d) 4

View Answer

Answer: c [Reason:] For one rotor revolution there are three power strokes in a Wankel engine.

3. Diesel engine is not employed in which of the following
a) Pumping sets
b) Air compressors
c) Tractors
d) Motorcycles

View Answer

Answer: d [Reason:] Diesel engines are not used in motorcycles.

4. Which of the following is not an arrangement of ic engine cylinders
a) Radial
b) Circular
c) V type engine
d) Opposed cylinder engine

View Answer

Answer: b [Reason:] Circular arrangement is not used for ic engine cylinders.

5. Which of these is a cylinder head type of an ic engine
a) X head
b) U head
c) F head
d) C head

View Answer

Answer: c [Reason:] Cylinders with F type head are very common.

6. Which of these is not a cylinder head type of an ic engine
a) L head
b) I head
c) T head
d) X head

View Answer

Answer: d [Reason:] X head type engines are not in use.

7. What is the disadvantage of using diesel engine in comparison to petrol engine
a) Higher weight-to-power ratio
b) Higher maintenance cost
c) Greater starting difficulties
d) All of the mentioned

View Answer

Answer: d [Reason:] All the given are the disadvantages of using a diesel engine over petrol engine.

8. Engines used in tractors are
a) Single cylinder engines
b) Two cylinder engines
c) Four cylinder engines
d) Six cylinder engines

View Answer

Answer: b [Reason:] Two cylinder engine is used in tractors.

9. Engines used in Ashok Leyland Comet trucks are
a) Single cylinder engines
b) Two cylinder engines
c) Four cylinder engines
d) Six cylinder engines

View Answer

Answer: d [Reason:] Ashok Leyland Comet trucks use six cylinder engines.

10. W-type arrangement in twelve and sixteen cylinder engines has
a) One row of cylinders
b) Two rows of cylinders
c) Three rows of cylinders
d) Four rows of cylinders

View Answer

Answer: c [Reason:] W type arrangement has three rows of cylinders.

11. The angle between two cylinders in a two cylinder V-type engine is usually
a) 15 degrees
b) 45 degrees
c) 60 degrees
d) 90 degrees

View Answer

Answer: c [Reason:] The angle between the cylinders is usually 60 degrees.

Set 5

1. What is actual power delivered by the engine known as?
a) Shaft power
b) Horse power
c) Brake power
d) None of the mentioned

View Answer

Answer: c [Reason:] The power delivered by the engine is called brake power.

2. If ‘T’ is torque(in Nm) and ‘N’ is speed(in rpm) then the required expression for Brake power ‘B.P’ in kWs is
a) 2πNT/6000
b) 2πNT/60000
c) πNT/6000
d) πNT/60000

View Answer

Answer: b [Reason:] The required expression is B.P = 2πNT/60000.

3. The torque available at the contact between road and driving wheel is called
a) Brake power
b) Friction power
c) Tractive effort
d) Engine torque

View Answer

Answer: c [Reason:] The torque between road and wheel is called tractive effort.

4. If ‘V’ is vehicle speed(in metres/min) and ‘R’ is radius of driving wheel(in metres) then the rpm of the driving wheel is given by
a) rpm = V/2πR
b) rpm = 2πV/R
c) rpm = πR/V
d) rpm = πV/R

View Answer

Answer: a [Reason:] The rpm of the driving wheel can be expressed as rpm = V/2πR.

5. Which of these is not a power loss which takes place between engine and driving wheel
a) Power loss due to friction of piston bearings and gears
b) Power loss from clutch to drive wheel due to friction of various parts
c) Transmission line loss
d) None of the mentioned

View Answer

Answer: d [Reason:] All the above mentioned losses are encountered while transmission of power.

6. The force that opposes the motion of a vehicle is
a) Rolling resistance
b) Gradient resistance
c) Wind or air resistance
d) All of the mentioned

View Answer

Answer: d [Reason:] Rolling resistance, gradient resistance and air resistance all oppose the motion of a vehicle.

7. Rolling resistance doesnot depend on which of the following factors
a) Load on each road wheel
b) Radius of driving wheel
c) Wheel inflation pressure
d) Nature of road surface

View Answer

Answer: b [Reason:] Rolling resistance does not depend on radius of driving wheel.

8. For an average type of road surface what percentage of vehicle’s weight constitutes rolling resistance
a) 5 to 10%
b) 1 to 2%
c) 2 to 5%
d) 0 to 3%

View Answer

Answer: b [Reason:] On an average road surface rolling resistance is 1 to 2% of vehicle’s weight.

9. Wind or air resistance depends on which of the following factors
a) Shape and size of vehicle body
b) Air velocity
c) Speed of vehicle
d) All of the mentioned

View Answer

Answer: d [Reason:] Air resistance on a vehicle depends on all the above mentioned factors.

10. If ‘k’ is coefficient of air resistance, ‘A’ is frontal area projected by the vehicle in square metres and ‘V’ is vehicle speed(in km/h) then the expession for air resistance ‘A.R’ on the vehicle is
a) A.R = k*A*V^2
b) A.R = k*A*V^3
c) A.R = 2k*A*V
d) A.R = k*A*V

View Answer

Answer: a [Reason:] The correct expression for air resistance is A.R = k*A*V2.

11. The value of coefficient of air resistance for average cars is approximately equal to
a) 0.32
b) 0.032
c) 0.0032
d) 1.32

View Answer

Answer: c [Reason:] For average cars, value of coefficient of air resistance is approx 0.0032.

12. One Horse Power(H.P) is approximately equal to _____ Watts.
a) 810
b) 545
c) 634
d) 746

View Answer

Answer: d [Reason:] 1 H.P = 746 Watts.

13. Gradient resistance for a vehicle depends on which of the following factors
a) Weight of the vehicle
b) Size of the vehicle
c) Width of tyres
d) Speed of the vehicle

View Answer

Answer: a [Reason:] Gradient resistance depends on weight of the vehicle.

14. Power to weight ratio for high performance cars can range upto
a) 150
b) 190
c) 230
d) 280

View Answer

Answer: c [Reason:] The ratio of power to weight of high performance cars can range as high as 230.

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