ELECTRICAL MCQ

1. Two winding's of a transformer are designated as

(a) primary and secondary winding's

(b) primary and h.v. winding's

(c) secondary and 1 v winding's or primary and 1 v winding's

(d) h.v. and 1.v. winding's

2. Two transformers A and B,having identical ratings, are to be designed

with flux densities of 1.2 T and 1.4 T respectively. The weight of

transformer A per kVA would be

(a) less than that of tanformer B

(b) more than that of transformer B

(c) equal to that of transformer B

(d) may be less or moe than that of transformer B depending upon

other perameters

3. In power transformers, core is made up of

(a) cast iron             (b) silicon steel   

(c) ferrite                 (d)powdered alloy

4. Consider the following statements

(a) Air-core transformers are used in gate-triggering circuits of

thyristor's

(b) Cores made of soft-ferrite are used in pulse transformers

(c) Air-core transformers are used in radio devices

(d) Cors of powdered alloy are used in isolation tranformers

From above, the correct answer is

(a) 2, 3, 4                  (b) 2, 3

(c) 1, 3, 4                  (d) 2, 4

5. For a given cross-sectional area of transformer core, stepped cores

are used

(a) to reduce the core loss

(b) to provide more mechanical strength to the core

(c) to reduce the conductor material and therefore I2R loss

(d) to reduce the magnetizing current

6. In single-phase core-type transformers, LV and HV winding's are

arranged as under

(a) L.V. on one core-limb, H.V. on the other core-limb

(b) half H.V.near the core and half L.V. outside the H.V. on each

limb

(c) L.V. and H.V. winding sections are sandwiched

(d) half L.V. near the core and half H.V. outside the L.V. on each

limb

7. A 400/200 V, 50 Hz transformer operates at a flux density of 1.2 T

when energised from its H.V. side. For this transformer, linear dimensions of core are doubled while the umber of turns are halved on both its

H.V. and L.C. sides. If this transformer is now connected to 800 V, 50

Hz on its H.V. side, then its flux density would be

(a) 0.6 T                (b) 1.2 T

(c) 3.6 T                (d) 4.8 T

8. For core-type power transformers, both primary and secondary winding's

have circular coil sections, because this section

(a) is easier to wind

(b) requires minimum conductor material and, therefor , less I²R

loss

(c) has the strongest mechanical shape

(d) results in less core material and, therefor, less core loss

9. Transformer action requires a

(a) constant magnetic flux       (b) increasing magnetic flux

(c) alternating magnetic flux   (d) alternating electric flux

10. In a single- phase transformer, with subscripts 1 and 2 for primary and

secondary windings.

(a) E1N2 = E2N1 and I1N1 = I2N2 (b) E1N1 = E2N2 and I1N1 = I2N2

(c) E1N2 = E2N1 and I1N2 = I2N1 (d) E1N1 = E2N2 and I1N2 = I2N1

11. The flux involed in the emf equation of a transformer has

(a) rms value           (b) average value

(c) total value          (d) maximum value

12. For understanding the behavior of a transformer, the following laws

may be called for.

1. Lenz’s law              2. Newton’s second law

3. Faraday’s law of     4. Ohm’s law

electromagnetic induction

5. Fleming’s right hand rule 6. Right-hand grip rule

From these, the correct answer is

(a) 1, 3, 4                   (b) 2, 3, 4, 5 

(c) 1, 3, 4, 5, 6           (d) 1, 3, 4, 6

13. In an ideal trasformer, If K is some constant, then the supply voltage

V, in terms of its magnetizing current Im can be expressed as

(a) jKfIm                   (b)jK.f/Im 

(c) – jK.fIm               (d)-jK.f/Im

14. In an ideal transformer, the impedance can be transformed from one

side to the other

(a) in direct proportion to square of turns-ratio

(b) in direct proportion to turns- ratio

(c) in inverse proportion to square of turns-ratio

(d) in inverse proportion to turns-ratio

               

ANSWERS:

                       1 (d)  2(b)  3 (b)   4 (b)    5 (c)     6 (d)    7 (b)

                       8 (c)  9(c)   10 (a)  11 (d)  12 (d)  13 (a)  14 (a)