Sunday, March 4, 2012

RRB Junior engineer(electrical) Model Questions

1. The frequency of DC current
(a) Equal to voltage magnitude
(b) 0
(c) Double of AC frequency
(d) 50 HZ
Ans : b
2. The current flowing in a purely inductive circuit of 30 mH on application of 230 V,
50 Hz single phase supply is 24.4 A. If the frequency of the applied voltage is
increased to 100 Hz the current flowing in the same circuit will be
(a) 24.4 A
(b) 48.8 A
(c) 12.2 A
(d) 6.1 A
Ans : c
3. Find the total resistance when two 3 Ohm resistances are connected in parallel.
(a) 1.11 ohms
(b) 1.5 ohms
(c) 0.707 ohms
(d) 1.23 ohms
Ans : b
4. Voltage drop in a resistance given by
(a) mmf/reluctance
(b) IR
(c) I/R
(d) VI
Ans : b
5. Off-line converter, SMPS has
a. AC input and dc output
b .DC input and dc output
c. AC input and ac output
d. None
Ans. a
6. Filter circuits are constructed by means of
a. Diode
b. Resistors
c. Transformers
d. Capacitor and inductors
Ans. d
7. Resistance of the diode is decreased when
a. Forward biased
b. Reverse biased
c. Both forward and reverse biased
d. Either a or b
Ans. a
8. In earlier time is used for voltage regulation.
a. Diode
b. Transistors
c. Vacuum tubes and glow bulbs
d. SMPS
Ans. c
9. is the equipment used during power failure.
a. Rectifier
b. Voltage regulators
c. UPS
d. SMPS
Ans. c
10. Peak factor of the sine wave is equal to
(a) 0.901
(b) 1.414
(c) 1.1
(d) 1.11
Ans :b
11. The amplitude of current of full wave rectified sinusoidal wave is 80 A, its average
value will be
(a) 25.44A
(b) 80A
(c) 40A
(d) 56.56A
Ans : a
12.Find the total current supplied to the lamp rated 100w .when supply voltage is 200 v.
(a) 1.75A
(b) 2A
(c) 0.5A
(d) 1A
(e) Ans : c
13. The power factor of a inductive circuit is
(a) Lagging
(b) Leading
(c) Zero lagging
(d) Unity
Ans : a
14. The power factor of a purely capacitive circuit is always
(a) Lagging
(b) Leading
(c) Unity
(d) Zero lagging
Ans : b
15. The overall circuit power factor of a RLC series circuit is found to be 0.898 lagging. The nature of the resultant circuit is
(a) Resistive
(b) Inductive
(c) Capacitive
(d) None of these
Ans : b
16. The maximum, rms and average value of a periodic current wave form is 100 A,
64.42A and 57.5A, respectively. The peak factor of this wave is
(a) 0.644
(b) 1.552
(c) 1.12
(d) None of these
Ans : b
17. In a parallel resistance circuit
(a) Power is same in all resistance
(b) Current is same in all resistance
(c) Voltage is same in all resistance
(d) Resistances are same
Ans : c
18. Find the total resistance when 2 Ohm and 4 Ohm resistances are in parallel.
(a) 1.33 Ohms
(b) 0.33 Ohms
(c) 2.33 Ohms
(d) 1 Ohm
Ans : a
19. Expression for mmf in terms of field strength is
(a) HI
(b) H/I
(c) HL
(d) H/L
Ans : c
20. is the property of magnetic which opposes the flow of flux through it.
(a) Resistance
(b) MMF
(c) Reluctance
(d) emf
Ans : c
21. is the property of electrical conductor which oppose the flow of current through it
(a) Reluctance
(b) emf
(c) mmf
(d) Resistance
Ans : d
22. Reluctance is expressed in
(a) Ampere Weber
(b) Ohm
(c) Ampere/Weber
(d) Volt/Ampere
Ans : c
23. Reciprocal of reluctance is termed as
(a) Conductance
(b) Permenance
(c) Permeability
(d) None of these
Ans : b
24. Ohm’s law for electric circuit will be
(a) emf= current/resistance
(b) emf= current X resistance
(c) emf= resistance/current
(d) emf= 1/( resistance X current)
Ans : b
25. Ohm’s law for magnetic circuit will be
(a) mmf= flux /resistance
(b) flux= mmf X resistance
(c) reluctance = mmf/ flux
(d) Resistance= mmf X flux
Ans : c

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