**Points :**single phase motors, multiple choice questions and answers, electrical objective type question answers, mcqs

The full-load efficiency of a shaded pole motor is about ……………

(i) 70 to 80%(ii) 60 to 70%(iii)**30 to 35%**(iv) 5 to 10%A vacuum cleaner employs motor.

(i) resistance split-phase(ii) capacitor-start(iii) shaded-pole motor(iv)**single-phase series motor**The direction of split-phase induction motor can be reversed by interchanging the connections of supply of ............

(i)**either main or starting winding**(ii) both main and starting winding(iii) rotor winding(iv) none of the aboveFor the same rating, the efficiency of a single-phase induction motor is .............. that of 3-phase induction motor.

(i)**less than**(ii) the same as(iii) more than(iv) none of the aboveMost of single-phase induction motors are …………. machines.

(i) 2-pole(ii) 6-pole(iii) 8-pole(iv)**4-pole**The main winding and starting winding of a single-phase induction motor are connected in ............ across the supply.

(i) series(ii)**parallel**(iii) series-parallel(iv) none of the aboveThe starting winding of a single-phase induction motor has ............... that of main winding.

(i) more poles than(ii) less poles than(iii)**same number of poles as**(iv) none of the aboveA 50 Hz, 4-pole single phase motor will have a synchronous speed of

(i)**1500 r.p.m**(ii) 750 r.p.m(iii) 1200 r.p.m(iv) none of the aboveA 1/3 H.P., 120V, 60 Hz capacitor-start motor has the following constants for the main and starting windings:

Main winding : Z_{m}= (4.5 + j 3.7) ohms

Starting winding : Z_{s}= (9.5 + j 3.5) ohms

The value of starting capacitance that will place the main and starting winding currents in quadrature at starting is(i) 212 µF(ii)**177 µF**(iii) 315 µF(iv) 424 µFThe direction of rotation of shaded-pole motor depends upon ..............

(i) supply frequency(ii) number of poles on the stator(iii)**which half of the pole is shaded**(iv) supply voltageIn a single-phase induction motor, speed-sensitive centrifugal switch is connected in …………. winding.

(i) parallel with main(ii) series with main(iii)**series with starting**(iv) parallel with startingA 4-pole, 50 Hz single-phase induction motor is running with a slip of 3.4%. The speed of the motor is

(i) 1279 r.p.m.(ii) 1120 r.p.m.(iii)**1449 r.p.m.**(iv) 1540 r.p.m.If I

_{m}and I_{s}are the currents in the main and starting windings respectively and α is the angle between I_{m}and I_{s}then motor torque T is given by ……………(i) T α I_{m}I_{s}cos α(ii)**T α I**_{m}I_{s}sin α(iii) T α I_{m}I_{s}(iv) none of the aboveWhich of the following single-phase motor is available with speed as low as one revolution per month?

(i)**shaded-pole**(ii) reluctance(iii) hysteresis(iv) universalThe purpose of starting winding in a single-phase induction motor is to ..............

(i) reduce losses(ii) limit temperature rise of the machine(iii)**produce rotating flux in conjunction with main winding**(iv) none of the aboveThe resistance split-phase induction motor has starting torque.

(i) high(ii)**moderate**(iii) very low(iv) none of the aboveThe resistance split-phase induction motors are the most popular single-phase motors because of …………..

(i)**their low cost**(ii) their high starting torque(iii) the long starting period(iv) none of the aboveIn a capacitor-start, capacitor-run motor, winding is cut out after starting.

(i) starting(ii) main(iii)**neither starting nor main**(iv) none of the aboveAt starting, the winding of a 220V, 50 Hz split-phase induction motor have the following values:

Main winding : R = 10 Ω ; X_{L}= 25 Ω

Starting winding : R = 25 Ω ; X_{L}= 15 Ω

What is the power factor of the motor?(i) 0.85 lag(ii)**0.64 lag**(iii) 0.52 lag(iv) 0.707 lagFor the same rating, the p.f. of a single-phase induction motor is ............... that of 3-phase induction motor.

(i) the same as(ii)**less than**(iii) more than(iv) none of the aboveA capacitor-start, capacitor-run motor has ...........

(i) low power factor(ii)**high power factor**(iii) low efficiency(iv) high starting torqueThe capacitor-start, capacitor-run induction motor acts as a true 2-phase motor at …………

(i) starting(ii) no load(iii) all loads(iv)**full-load**The capacitor-start, capacitor-run motor is used in those applications where

(i) high starting torque is required(ii)**silence is important**(iii) noisy operation is not important(iv) none of the aboveThe capacitor-start, capacitor-run motor has ………..

(i)**no centrifugal switch**(ii) low power factor(iii) noisy operation(iv) low efficiencyCapacitor motors .............. resistance split-phase induction motors.

(i)**are costlier than**(ii) are less costly than(iii) cost about the same as(iv) poor starting torque thanMost of the troubles of single phase induction motors are traceable to the............,....

(i) rotor bars(ii) main winding(iii) shaft bearings(iv)**starting switch**The single phase shaded pole motor has …………….

(i)**squirrel cage rotor**(ii) wound rotor(iii) high power factor(iv) high starting torqueThe resistance split-phase induction motor is used in those applications where …………

(i) starting is frequent(ii) starting period is long(iii)**starting is infrequent**(iv) none of the aboveA 4-pole, 50 Hz single-phase induction motor has a slip of 5 %. The speed of the motor will be ……………….

(i) 1500 r.p.m(ii)**1425 r.p.m**(iii) 1200 r.p.m(iv) none of the aboveAt starting, the line current of a capacitor-start induction motor is ............... the normal full-load current.

(i) 8 to 10 times(ii)**4 to 5 times**(iii) equal to(iv) 7 to 8 timesThe single phase series motor can operate on …………….

(i) a.c. only(ii) d.c. only(iii)**both a.c. and d.c**(iv) none of the aboveFor the same rating, a d.c. series motor costs single phase series motor.

(i) about the same as(ii) more than(iii)**less than**(iv) none of the aboveA 2 H.P. d.c. series motor will weigh 2 H.P. single phase series motor.

(i) about the same as(ii)**less than**(iii) more than(iv) none of the aboveThe best suited motor to drive 1/4 H.P. fan in a hospital ward would be ................ motor.

(i) shaded-pole(ii) single-phase series motor(iii)**capacitor-run motor**(iv) hysteresis motorThe washing machine generally employs ………. motor.

(i) single-phase series motor(ii)**resistance split-phase**(iii) shaded-pole(iv) hysteresisThe best suited motor to drive 3/4 H.P. air compressor would be ............... motor.

(i) capacitor-start(ii)**single-phase series**(iii) shaded-pole(iv) resistance split-phaseA single-phase induction motor employs rotor.

(i)**squirrel cage**(ii) wound(iii) either squirrel cage or wound(iv) none of the aboveThe least expensive fractional horse power motor is ............. motor.

(i)**shaded-pole**(ii) capacitor-start(iii) split-phase(iv) a.c. seriesA 4-pole, 250 W, 115 V, 60 Hz capacitor start induction motor takes a full-load line current of 5.3A while running at 1760 r.p.m. The full-load efficiency of the motor is 64%.

The slip is(i) 4.3%(ii) 1.8%(iii) 8.3 %(iv)**2.2 %**A 4-pole, 250 W, 115 V, 60 Hz capacitor start induction motor takes a full-load line current of 5.3A while running at 1760 r.p.m. The full-load efficiency of the motor is 64%.

The motor power factor is(i)**0.64 lag**(ii) 0.32 lag(iii) 0.707 lag(iv) 0.85 lagA 4-pole, 250 W, 115 V, 60 Hz capacitor start induction motor takes a full-load line current of 5.3A while running at 1760 r.p.m. The full-load efficiency of the motor is 64%.

The full-load torque is(i) 2.6 N-m(ii)**1.35 N-m**(iii) 4.5 N-m(iv) 7.8 N-mA 200 W, 230 V, 50 Hz capacitor-start motor has the following winding parameters:

Main winding : R = 4.5 Ω ; X_{L}= 3.7 Ω

Starting winding : R = 9.5 Ω ; X_{L}= 3.5 Ω

What should be the angle between input voltage and starting winding current to give maximum starting torque?(i) 38.2ᵒ(ii) 24.6ᵒ(iii)**50.4ᵒ**(iv) 32.7ᵒA 200 W, 230 V, 50 Hz capacitor-start motor has the following winding parameters:

Main winding : R = 4.5 Ω ; X_{L}= 3.7 Ω

Starting winding : R = 9.5 Ω ; X_{L}= 3.5 Ω

What should be the capacitance of the starting capacitor that will result n the maximum starting torque?(i) 104 µF(ii) 189 µF(iii) 304 µF(iv)**212 µF**The nameplate of a 1-phase, 4-pole induction motor gives the following data:

Output 373W ; 230V, Frequency 50 Hz ; Input current 2.9A Power factor 0.71 ; speed 1410 r.p.m. The full-load slip of the motor is(i)**6%**(ii) 2%(iii) 4 %(iv) 3 %For the same rating, the size of a single-phase induction motor is about .............. that of the corresponding 3-phase induction motor.

(i) 3 times(ii) the same as(iii)**1.5 times**(iv) 0.33 timesThe nameplate of a 1-phase, 4-pole induction motor gives the following data:

Output 373W ; 230V, Frequency 50 Hz ; Input current 2.9A Power factor 0.71 ; speed 1410 r.p.m. what is the efficiency of the motor?(i) 65.3%(ii)**78.7%**(iii) 89.2%(iv) 70.6%At starting, the winding of a 220V, 50 Hz split-phase induction motor have the following values:

Main winding : R = 10 Ω ; X_{L}= 25 Ω

Starting winding : R = 25 Ω ; X_{L}= 15 Ω

What is the phase angle between I_{m}and I_{s}?(i) 21.2ᵒ(ii) 49.4ᵒ(iii)**37.7ᵒ**(iv) 32.6ᵒAt starting, the winding of a 220V, 50 Hz split-phase induction motor have the following values:

Main winding : R = 10 Ω ; X_{L}= 25 Ω

Starting winding : R = 25 Ω ; X_{L}= 15 Ω

What is the starting torque if k = 0.53?(i) 15 N-m(ii) 31 N-m(iii)**20 N-m**(iv) 48 N-mAt starting, the winding of a 220V, 50 Hz split-phase induction motor have the following values:

Main winding : R = 10 Ω ; X_{L}= 25 Ω

Starting winding : R = 25 Ω ; X_{L}= 15 Ω

What is the line current?(i)**14.9 A**(ii) 8.7 A(iii) 21.2A(iv) 13.7 AAt starting, the winding of a 220V, 50 Hz split-phase induction motor have the following values:

Main winding : R = 10 Ω ; X_{L}= 25 Ω

Starting winding : R = 25 Ω ; X_{L}= 15 Ω

A 160 µF capacitor is connected in series with the starting winding of the motor. The phase displacement between I_{m }, and I_{s}is?(i) 41.5ᵒ(ii)**83.7ᵒ**(iii) 79.2ᵒ(iv) 64.5ᵒAt starting, the winding of a 220V, 50 Hz split-phase induction motor have the following values:

Main winding : R = 10 Ω ; X_{L}= 25 Ω

Starting winding : R = 25 Ω ; X_{L}= 15 Ω

A 160 µF capacitor is connected in series with the starting winding of the motor.

What will be the value of starting torque?(i)**36.7 N-m**(ii) 19.8 N-m(iii) 24.5 N-m(iv) 41.2 N-mA single-phase induction motor runs normally at 1125 r.p.m. on 60 Hz power supply. How many poles must it have?

(i) 8(ii)**6**(iii) 4(iv) 2A single phase motor runs normally at 183 rad/sec on 60 Hz power supply. How many poles must it have?

(i) 10(ii) 8(iii) 12(iv)**4**A 250 W resistance split-phase induction motor has the following currents in the various windings at the moment of starting:

Main winding current, I_{m}= 9 A at ф_{m}= 40.5ᵒ lag

Starting winding current, I_{s}, = 6A at ф_{s}= 15.5ᵒ lag

What is the component of the 4 in phase with the line voltage?(i)**6.844 A**(ii) 3.862 A(iii) 8.626 A(iv) none of the aboveA 250 W resistance split-phase induction motor has the following currents in the various windings at the moment of starting:

Main winding current, I_{m}= 9 A at ф_{m}= 40.5ᵒ lag

Starting winding current, I_{s}, = 6A at ф_{s}= 15.5ᵒ lag

What is the quadrature component of starting winding current?(i) −2.51A(ii)**−1.603A**(iii) −3.525A(iv) none of the aboveIn a split-phase inductor motor, the two stator windings

(i) have equal R/X_{L}ratio(ii)**are mutually displaced by 90ᵒ electrical**(iii) draw only the in-phase currents(iv) draw equal currentsAs compared to capacitor-start induction motors or split-phase motors, a permanent-split capacitor motor has lower

(i) efficiency(ii) cost(iii)**noise**(iv) power-factorA resistance split-phase induction motor is used for

(i)**low inertia loads**(ii) high inertia loads(iii) very high inertia loads(iv) none of the above

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