BASIC ELECTRICAL
MULTIPLE CHOICE QUESTIONS
Time: 40mins
Maximum marks :160
Each
correct answer carries 4 mark. Wrong answer has negative of 1 mark
1 The two windings of a transformer is
(A) conductively linked. (B) inductively linked.
(C) not linked
at all. (D) electrically linked.
2) The d.c. series motor
should always be started with load because
(A) at no load, it will rotate at dangerously high speed.
(B) it will fail to start.
(C) it will not develop high starting torque.
(D) all are
true.
3) The
frequency of the rotor current in a 3 phase 50 Hz, 4 pole induction motor at
full
load
speed is about
(A) 50 Hz. (B) 20 Hz.
(C) 2 Hz. (D)
Zero.
4) The
generation voltage is usually
(A) between 11 KV and 33 KV. (B) between 132 KV and 400 KV.
(C) between
400 KV and 700 KV. (D) None of the above.
5) In a d.c. series motor the electromagnetic
torque developed is proportional to
(A) Ia . (B) I_a^2
(C) 1/I_a (D) 1/I_a^2
6) A ceiling fan uses
a) dc series motor b) dc shunt motor
c) single phase induction motor d) synchronous motor
7) The drive motor used in a mixer-grinder is a
(A) dc motor. (B) induction motor.
(C) synchronous
motor. (D) universal motor
8) A 50
Hz, 3-phase induction motor has a full load speed of 1440 r.p.m. The number of
poles
of the motor are
(A) 4. (B) 6.
(C) 12. (D)
8.
9) A 4
pole lap wound dc shunt motor rotates at the speed of 1500 rpm, has a flux of
0.4
mWb and
the total number of conductors are 1000. What is the value of emf?
(A) 100 Volts. (B) 0.1 Volts.
(C) 1 Volts. (D) 10 Volts.
10) The
rotor frequency for a 3 phase 1000 RPM 6 pole induction motor with a slip of
0.04
is________Hz
(A) 8 (B) 4
(C) 6 (D) 2
11) A
commutator in a d.c. machine
(A) Reduces power loss in armature.
(B) Reduces power loss in field circuit.
(C) Converts the induced a.c armature voltage into direct voltage.
(D) Is not
necessary.
12) The
efficiency of a transformer is mainly dependent on
(A) core losses. (B) copper losses.
(C) stray
losses. (D) dielectric losses.
13) A
3-phase, 400 votts, 50 Hz, 100 KW, 4 pole squirrel cage induction motor with a
rated
slip of 2% will have a rotor speed of
(A) 1500 rpm (B) 1470 rpm
(C) 1530 rpm (D)
1570 rpm
14) Low
head plants generally use
(A) Pelton Turbines (B) Francis Turbine
(C) Pelton or
Francis Turbine (D) Kaplan Turbines
15) A
400kW, 3-phase, 440V, 50Hz induction motor has a speed of 950 r.p.m. on
fullload.
The
machine has 6 poles. The slip of the machine will be _______________.
(A) 0.06 (B) 0.10
(C) 0.04 (D)
0.05
16) The
armature of a dc machine is laminated to reduce:
(A) Eddy current loss (B) Hysteresis loss
(C) copper losses
(D) friction and windage losses
17) SI unit of electrical energy is
(A) Joule (B) kilowatt
(C) kilowatthour
(D) newton
18) Resistance is analogous to ____ of
magnetic circuit.
(A) Flux (B) reluctance
(C) permeance (D) conductance
19) A heater is rated 1000W, 230V. The value
230V represents
(A) rms value (B)
avg value
(C) dc value (D) peak
value
20) In an RLC series circuit, current is
maximum when the circuit is purely
(A) inductive (B)
capacitive
(C) resistive (D) resistive
and capacitive
21) Dc motor follows ____ principle
a) Cork screw rule b) Flemings left hand rule
c) Flemings right hand rule d) None
22) Control rod in nuclear reactor is made of
a) boron
b) cadmium c) graphite d) a or b
23) Demand
factor = ____
a)(Maximum
demand )/(Connected load) b) ( Connected load)/(Maximum demand)
c) (Average
load)/(Maximum demand) d) (Maximum demand)/(Average load)
24) Which of the statements are incorrect?
a) Circuit breakers are used to disconnect a circuit under load
b) Isolators are used to disconnect a circuit under no load
c) Circuit breakers are used to disconnect a circuit under no load
d) Instrument transformers are used for measurement and monitoring
purposes
25) Match the
items given in List – I and those in List – II . Select your answers using codes
given in the lists.
List – I (Material) List
– II (Temperature coefficient of resistance)
a) Aluminum P.
Negligibly small
b) Manganin Q.
Positive
c) Carbon R.
Negative
a) a→R,b→Q, c→P b) a→Q,b→P,c→R c) a→P,b→Q,c→R d) a→R;b→P;c→Q
26) In a
single phase transformer, core loss is 500W and copper loss is 600W. At maximum
efficiency what will be total loss?
a) 1200W b) 1100W
c) 1150W d) 1000W
27) In series
circuit, at resonance,
a) V=V_R b) X_L=X_C c) Z=R
d) all of these
28) Which
power station has higher initial cost?
a. Hydro
b. Gas c. Diesel d. Thermal
29) Time constant of inductive circuit
increases if
a) L increases, R decreases
b) L decreases, R decreases
c) L increases, R increases
d) L decreases, R increases
30) An emf of 16V is induced in a coil of
self inductance of 4H. Rate of change of current is ___ A/s.
a) 64 b)
32 c) 16 d) 4
ANSWERS
1) b
2) a
3) c
4) a
5) b
6) a
7) d
8) a
N= Ns
(1-S) = NS –NS x S
1440 = Ns (1-S)
Ns = 1440 / (1-S)
Ns = (120 f/ p) = 120 x 50/p = 6000 p
Ns will be closer to N i.e 1440
When P=2 ; Ns = 3000 rpm , not close to N
When P=4 ; Ns = 1500 rpm , it is closer to N
Therefore
P =4 for N=1440
9) d
Given N = 1500 rpm, F = 0.4 mWb, Z = 1000, P = 4,
& A= 4
Therefore,
Eb = NFPZ / 60 A
10) d
Given: N=1000 rpm ; P= 6; s= 0.04;
and f = NP/ 120
= 1000(6)/120
= 50 Hz
Rotor frequency fr=sf = 0.04(50)= 2.0 Hz
11) c
12) a
13) b
14) a
15) d
16) a
17) c
18) b
19) a
20) c
21) b
22) d
23) a
24) c
25) b
26) d
27) d
28) a
29) a
30) d
