Quiz: Electrical Engineering

Exam: SSC JE

Topic: Miscellaneous

Each question carries 1 mark.

Negative marking: 1/4 mark

Time: 10 Minute

Q1. A moving-iron ammeter produces a full-scale torque of 240 µNm with a deflection of 120⁰ at a current of 10 A. The rate of change of self-inductance (µH/radian) of the instrument at full scale is

(a)2.0 µH/radian

(b)4.8 µH/radian

(c)12.0 µH/radian

(d)114.6 µH/radian

Q2. In wiring and winding an abbreviation for S.W.G is:

(a)Synthetic winding guard

(b)Simple winding gauge

(c)Standard wire gauge

(d)Single wire guard

Q3. Overlapping of conduction band and valence band occurs in

(a)Conductors only

(b)Semiconductors only

(c)Insulators only

(d)Conductors and semiconductors both

Q4. The pressure coil of an energy meter is…….

(a)Purely resistive

(b) Purely inductive

(c)Highly resistive

(d)Highly inductive

Q5. In DC compound Motor the shunt field and series field winding are made up of _________ & ____________ respectively

(a)High Resistance, Low Resistance

(b)Low Resistance, High Resistance

(c)Equal Resistance

(d)None of the above

Q6. The energy in joules stored in the magnetic field of 0.15 H inductance with a

180 mAcurrent will be

(a) 2.43 J

(b) 2.43×10^(-3) J

(c) 2.43×10^(-6) J

(d) 2.43×10^(-9) J

Q7. A 4-pole, 3-phase induction motor is running at 4% slip at full load. If the speed of the motor is 750 rpm, the supply frequency is

(a) 162/3 Hz

(b) 26 Hz

(c) 50 Hz

(d) 60 Hz

Q8. Two coils have inductances L1 = 1200 mH and L2 = 800 mH. They are connected in such a way that flux in the two coils aid each other and inductance is measured to be 2500 mH, then Mutual inductance between the coils is ___________ mH.

(a)500

(b)250

(c)225

(d)150

Q9. The magnetic field required to applied in opposite direction to reduce the residual magnetism to zero is called

(a)Hysteresis

(b)Retentivity

(c)Coercivity

(d)none of these

Q10. An alternating current varying sinusoidally has a peak value of 50 A and a frequency of 10 Hz. Mathematical expression for the current is:

(a) i=50*√2 sin(2*π*10)t

(b) i=50/√2 sin(2*π*10)t

(c) i=50*√2 sin(π*10)t

(d) i=50 sin(2*π*10)t

SOLUTIONS

S1. Ans.(b)

Sol. moving-iron ammeter full torque is given as: T_c=1/2 I^2 dL/dӨ

∴dL/dӨ=(2×240×10^(-6))/10^2 =4.8 µH/radian

S2. Ans.(c)

Sol. S.W. G= Standard wire gauge

S3. Ans.(a)

Sol. overlapping of conduction and valence band occurs in conductors only.

S4. Ans.(d)

Sol. The pressure coil of an energy meter is highly inductive while for wattmeter it is highly resistive.

S5. Ans.(a)

Sol. In DC compound Motor:

The shunt-winding is made up of wires of small cross-sections and has high resistance and the series winding will carry a large armature current and therefore it is made of wires of large cross-section and has a few turns only.

S6. Ans.(b)

Sol. Energy stored in magnetic field

=1/2 LI²

=1/2×0.15×(0.18)^2

=2.43×10^(-3) J

S7. Ans.(b)

Sol. S= 4% Nr =750 rpm

∴ Ns=Nr/((1-S))

=750/0.96

=781.25 rpm

But Ns = (120 f)/P

∴ (781.25×4)/120=f

⇒ f = 26 Hz

S8. Ans.(b)

Sol. Flux in two coils aid each other inductor of the combination

So, the mutual inductance is 250 mH.

S9. Ans.(c)

Sol. from the B-H curve, the value of magnetising field requires to reduce residual magnetism to zero is called coercivity of the material.

RETENTIVITY: The value of the intensity of magnetisation of a material when the magnetising field is reduced to zero is called retentivity.

S10. Ans.(d)

Sol. i=im sin(2πf)t