BASIC ELECTRICAL PART-4

BASIC ELECTRICAL PART 4

176. Two coils have self-inductances of 10 H and 2 H, the mutual
inductance being
zero. If the two coils are connected in series, the total inductance will be
(a) 6 H
(b) 8 H
(c) 12 H
(d) 24 H
Ans: c
177. In case all the flux from the current in coil 1 links with coil 2, the coefficient
of coupling will be
(a) 2.0
(b) 1.0
(c) 0.5
(d) zero
Ans: b
178. A coil with negligible resistance has 50V across it with 10 mA. The
inductive
reactance is
(a) 50 ohms
(b) 500 ohms
(c) 1000 ohms
(d) 5000 ohms
Ans: d
179. A conductor 2 meters long moves at right angles to a magnetic field
of flux
density 1 tesla with a velocity of 12.5 m/s. The induced e.m.f. in the
conductor will
be
(a) 10 V
(6) 15 V
(c) 25V
(d) 50V
Ans: c
180. Lenz’s law is a consequence of the law of conservation of
(a) induced current
(b) charge
(c) energy
(d) induced e.m.f.
Ans: c
181. Two 300 uH coils in series without mutual coupling have a total
inductance of
(a) 300 uH
(b) 600 uH
(c) 150 uH
(d) 75 uH
Ans: b
182. Current changing from 8 A to 12 A in one second induced 20 volts in a coil.
The value of inductance is
(a) 5 mH
(b) 10 mH
(c) 5 H
(d) 10 H
Ans: c
183. Which circuit element(s) will oppose the change in circuit current ?
(a) Resistance only
(b) Inductance only
(c) Capacitance only
(d) Inductance and capacitance
Ans: b
184. A crack in the magnetic path of an inductor will result in
(a) unchanged inductance
(b) increased inductance
(c) zero inductance
(d) reduced inductance
Ans: d
185. A conductor carries 125 amperes of current under 60° to a magnetic field of 1.1
tesla. The force on the conductor will be nearly
(a) 50 N
(b) 120 N
(c) 240 N
(d) 480 N
Ans: b
186. Find the force acting on a conductor 3m long carrying a current of 50
amperes
at right angles to a magnetic field having a flux density of 0.67 tesla.
(a) 100 N
(b) 400 N
(c) 600 N
(d) 1000 N
Ans: a
187. The co-efficient of coupling between two air core coils depends on
(a) self-inductance of two coils only
(b) mutual inductance between two coils only
(c) mutual inductance and self inductance of two coils
(d) none of the above
Ans: c
188. An average voltage of 10 V is induced in a 250 turns solenoid as a
result of a
change in flux which occurs in 0.5 second. The total flux change is
(a) 20 Wb
(b) 2 Wb
(c) 0.2 Wb
(d) 0.02 Wb
Ans: d
189. A 500 turns solenoid develops an average induced voltage of 60 V.
Over what
time interval must a flux change of 0.06 Wb occur to produce such a
voltage ?
(a) 0.01 s
(b) 0.1 s
(c) 0.5 s
(d) 5 s
Ans: c
190. Which of the fpllowing inductor will have the least eddy current
losses ?
(a) Air core
(b) Laminated iron core
(c) Iron core
(d) Powdered iron core
Ans: a
191. A coil induces 350 mV when the current changes at the rate of 1 A/s.
The
value of inductance is
(a) 3500 mH
(b) 350 mH
(c) 250 mH
(d) 150 mH
Ans: b
192. A coil is wound on iron core which carries current I. The self-induced
voltage
in the coil is not affected by
(a) variation in coil current
(b) variation in voltage to the coil
(c) change of number of turns of coil
(d) the resistance of magnetic path
Ans: b
193. Nichrome wire is an alloy of
(a) lead and zinc
(b) chromium and vanadium
(c) nickel and chromium
(d) copper and silver
Ans: c
194. When a voltage of one volt is applied, a circuit allows one micro
ampere current to flow
through it. The conductance of the circuit is
(a) 1 n-mho
(b) 106 mho
(c) 1 milli-mho
(d) none of the above
Ans: a
195. Which of the following can have negative temperature coefficient ?
(a) Compounds of silver
(6) Liquid metals
(c) Metallic alloys
(d) Electrolytes
Ans: d
196. Conductance : mho ::
(a) resistance : ohm
(b) capacitance : henry
(c) inductance : farad
(d) lumen : steradian Ans: a
197. 1 angstrom is equal to
(a) 10-8 mm
(6) 10″6 cm
(c) 10″10 m
(d) 10~14 m
Ans: c
198. One newton meter is same as
(a) one watt (b) one joule
(c) five joules
(d) one joule second
Ans: b
199. A thermistor has
(a) positive temperature coefficient
(b) negative temperature coefficient
(c) zero temperature coefficient
(d) variable temperature coefficient
Ans: c
200. If/, R and t are the current, resistance and time respectively, then
according to Joule’s
law heat produced will be proportional to
(a) I2Rt
(b) I2Rf
(c) I2R2t
(d) I2R2t*

Ans: a