Quiz: Electrical Engineering 20 Aug 2020

Quiz: Electrical Engineering
Exam: RSMSSB-JEn
Topic: Miscellaneous

Each question carries 1 mark.
Negative marking: 1/3 mark
Time: 10 Minute

Q1. 8 pole, DC generator has a simplex wave-wound armature containing 32 coils of 6 turns each. Its flux per pole is 0.06 Wb. The machine is running at 250 rpm. The induced armature voltage is:
(a)96 V
(b)192 V
(c)384 V
(d)768 V

Q2. How many 200 W/220V incandescent lamps connected in series would consume the same total power as a single 100 W/220V incandescent lamp?
(a)1
(b)2
(c)3
(d)Not possible

Q3. The surge impedance of 400 km long over-head transmission line is 300 Ω. For a 200 km length of the same transmission line surge impedance will be
(a)75 Ω
(b)150 Ω
(c)300 Ω
(d)600 Ω

Q4. In a dynamometer type wattmeter, the pressure coil connected across the load terminal is
(a) Highly inductive
(b) Highly capacitive
(c) Highly resistive
(d) Non inductive

Q5. Due to the inductance in the pressure coil of dynamometer type wattmeter, the reading will be
(a) High for both leading and lagging power factors
(b) Low for both leading and lagging power factors
(c) High for lagging power factor and low for leading power factor
(d) Low for lagging power factor and high for leading power factor

Q6. One unit of electrical energy equals
(a)1 KWH
(b)1 WH
(c)10 WH
(d)100 WH

Q7. If the applied voltage of a DC motor is 230 V, then back emf, for maximum power developed is
(a)460 V
(b)230 V
(c)200 V
(d)115 V

Q8. A 50-volt AC is applied across an RC (series) network. The rms voltage across the resistance is 40 V, then the potential across the capacitance will be
(a) 40 V
(b) 10 V
(c) 20 V
(d) 30 V

Q9. Which of the following option is true for resonance condition in series RLC circuits?
(a) X_L=R
(b) X_L>X_C
(c) X_C=R
(d) X_L=X_C

Q10. The efficiency of two identical transformers under loading can be determined by………test.
(a)Open circuit
(b)Short circuit
(c)No load
(d)Back to back

SOLUTIONS

S1. Ans.(c)
Sol. Eg=zϕNP/60A
Where, A=number of parallel paths=2 (for wave winding)
And Z= 2×32×6=384
∴Eg=zϕNP/60A=(384×0.06×250×8)/(60×2)=384 V

S2. Ans.(b)
Sol. For 200 W/220V incandescent lamp, R=V^2/P=220^2/200=242 Ω
And for 100 W/220V incandescent lamp, R_t=V^2/P=220^2/100=484 Ω
According to question, for series connection: R_t=n×R
⇒484=n×242
∴n=2

S3. Ans.(c)
Sol. The surge impedance is independent of the length of the transmission line. Hence it will be same as before i.e. 300Ω.

S4. Ans.(c)
Sol. In a dynamometer type wattmeter, the pressure coil connected across the load terminal is highly Resistive.

S5. Ans.(c)
Sol. Because of the inductance, the current of the pressure coils lags behind the voltage. Thus, the power factor of the wattmeter becomes lagging, and the meter reads high reading and vice-versa.

S6. Ans.(a)
Sol. One unit of electrical energy equals 1KWH.

S7. Ans.(d)
Sol. For maximum power output, the back emf is equal to half of the applied voltage.
Hence, Eb = V/2 = 230/2 ⇒115 V. where V is the terminal voltage.

Q8. Ans.(d)
Sol.

(VS )^2=(VR )^2+(VC )^2
(50)^2+(40)^2+(VC )^2
⇒ VC = √(2500-1600)
= 30 V

Q9. Ans.(d)
Sol. In case of series Resonance, X_L = X_C and Total impedance (z) = √(R^2+(XL-XC )^2 )
= √((R)^2+(0)^2 )
⇒ ▭(Z=R )
and Power factor (cosϕ) = R/Z=R/R=1
So, in series Resonance,
Z = Z(min )=R
pf = unity,

S10. Ans.(d)
Sol. The efficiency of two identical transformers under loading can be determined by back to back test.

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