Objective Type Questions for SSC JE Electrical

21. Which of the following motors can work satisfactory on both AC and DC?

(a) Synchronous motor
(b) Series motor
(c) Shunt motor
(d) Induction motor

22. Two alternators rated 40 MVA and 60 MVA respectively are working in parallel and supplying a total load of 80 MW. Speed regulation of both the alternators is 5%. Load participation between them would be

(a) 30 MW, 50 MW
(b) 32 MW, 48 MW
(c) 36 MW, 44 MW
(d) 40 MW each

Answer: (b) 32 MW, 48 MW

23. Slip of a 3-phase induction motor may be expressed as

(a) rotor power input/rotor copper loss
(b) rotor copper loss/rotor core loss
(c) rotor copper loss/rotor power input
(d) rotor copper loss/total input power

24. The emf induced per phase in a three phase star connected synchronous generator having the following data

Distribution factor = 0.955 | Coil-span factor = 0.966 | Frequency = 50 Hz | Flux per pole = 25 mwb | Turns per phase = 240
emf per phase is
(a) 1737.80 V
(b) 2128.36 V
(c) 1228.81 V
(d) 869.46 V

25. In a 1-phase transformer, the copper loss at full load is 600 W. At half of the full load the copper loss will be

(a) 300 W
(b) 150 W
(c) 75 W
(d) 600 W

26. An auto-transformer used with a sodium vapour lamp should have high

(a) transformation ratio
(b) winding resistance
(c) leakage reactance of windings
(d) VA rating

27. In an auto-transformer, the number of turns in primary winding is 210 and in secondary winding is 140. If the input current is 60 A, the currents in output and in common winding are respectively

(a) 90 A, 150 A
(b) 40 A, 20 A
(c) 40 A, 100 A
(d) 90 A, 30 A

Answer: (d) 90 A, 30 A

28. A 3-phase transformer has its primary connected in delta and secondary in star. Secondary to primary turns ratio per phase is 6. For a primary voltage of 200 V, the secondary voltage would be

(a) 58 V
(b) 2078 V
(c) 693 V
(d) 1200 V

Answer: (b) 2078 V

29. A resistance and another circuit element are connected in series across a DC voltage V. The voltage across the second element is V initially and zero after time. The other element is pure

(a) inductance
(b) capacitance
(c) both (b) and (d)
(d) resistance

30. For RLC AC series circuit at resonance the current is

(a) maximum at leading p.f
(b) minimum at leading p.f
(c) minimum at lagging p.f
(d) maximum at unity p.f

31. A series R-L-C circuit resonates at 1 MHz. At frequency 1.1 MHz the circuit impedance will be

(a) inductive
(b) resistive
(c) will depend on the relative amplitude of R, L and C
(d) capacitive

32. The equivalent resistance between terminals X and Y of the network shown is

(a) 20/9
(b) 8
(c) 100/3
(d) 40/3

33. Application of Thevenin’s Theorem in a circuit results in

(a) a voltage source and an impedance in series
(b) An ideal voltage soruce
(c) An ideal current source
(d) a current source and an impedance in parallel

34. A current of i = 6 +10sin(100pt) + 20sin(200pt) is flowing through a series combination of a PMMC and moving iron instrument. Ratio of the two currents as registered by the M.I. and PMMC meter is

(a) 2.63
(b) 1.81
(c) 3.11
(d) 2.82

Answer: (d) 2.82

35. Three resistances 5 ohms each are connected in star. Values of equivalent delta resistances are?

(a) 15 ohms each
(b) 1.5 ohms each
(c) 2.5 ohms each
(d) 5/3 ohms each

36. A 120 V, 60 W incandescent lamp has to be operated from 220 V, 50 c/s, 1-phase AC supply. In order to do this, a circuit element has to be connected in series with the lamp. Which one of the following series element is preferable ?

(a) Pure inductance
(b) Pure capacitance
(c) Pure inductance or capacitance
(d) Resistance

37. The bandwidth of an ac series circuit consisting of R, L and C is

(a) RC/L
(b) L/R
(c) R/L
(d) L/RC

38. For balanced 3-phase supply system, the phasor sum of the line currents is NOT zero if the load is

(a) Unbalanced star connected
(b) Balanced delta connected
(c) Unbalanced delta connected
(d) Balanced star connected

39. At series resonance of an ac R-L-C circuit the impressed voltage is

(a) equal to the inductive drop
(b) equal to the resistive drop
(c) equal to the capacitive drop
(d) greater than the resistive drop

40. In a series RLC circuit R = 20Ω, X_L = 30 Ω  and  X_L = 30 Ω  . If the supply voltage across the combination is v =100sin(100pt + 30^o) volts , the instantaneous current and the power factor of the circuit are respectively

(a) i = 5sin(100pt + 30^o)Amps , p.f . = 0.866
(b) i = 3.536sin(100pt + 30^o )Amps , p.f . = 0.866
(c) i = 5sin(100pt + 30^o)Amps , p.f . = unity
(d) i = 3.536sin(100pt + 30^o)Amps , p.f . = unity

Answer: (c)