Quiz Electrical Engineering

Exam: GATE

Topic: Miscellaneous

Date: 04/06/2021

Each Question carries 2 Mark

Negative Marking: 1/3

Time: 20 Minutes

Q1. A 4 KVA, 400/200 V, single-phase transformer has resistance of 0.02 pu and reactance of 0.06 pu. What is the value of its resistance and reactance referred to HV side?

(a) 1 Ω and 3 Ω

(b) 0.08 Ω and 0.24 Ω

(c) 0.8 Ω and 2.4 Ω

(d) 0.2 Ω and 0.6 Ω

Q2. If the applied voltage of a certain transformer is increased by 50 % and the frequency is reduced to 50 % (assuming that the magnetic circuit remains unsaturated), the maximum core flux will

(a) Remains the same as original

(b) Change to three times the original value

(c) Change to 0.5 times the original value

(d) Change to 1.5 times the original value

Q3. What happened to the speed when the flux is reduced by 10 % in a 200 V DC shunt motor having an armature resistance of 0.2 Ω carrying a current of 50 A and running at 960 rpm prior to weakening of field. The total torque may be assumed constant & neglect losses….

(a) 1250 rpm

(b) 576 rpm

(c) 920 rpm

(d) 1066 rpm

Q4. An amplifier has a gain of 20 without feedback. If 10% of the output voltage is fed back by means of resistance negative feedback circuit, the overall gain would be

(a) 19.80

(b) 16.55

(c) 10.85

(d) 6.67

Q5. Phase reversed of 180⁰ as compared to input occurs in the output of

(a) CE amplifier

(b) CB amplifier

(c) CC amplifier

(d) All of the above

Q6. A single phase, half-wave, controlled rectifier has 400 sin〖(314 t)〗 as the input voltage and R as the load. For a firing angle of 60⁰ for the SCR, the average output voltage is

(a) 200/π

(b) 240/ π

(c) 300/ π

(d) 400/ π

Q7. A single-phase energy meter having meter constant of 200 rev/kWh is operating on 230V, 50 Hz supply with a load of 10 A, and at unity power factor for three hours continuously. The number of revolutions shown by the meter during this period is

(a) 1380

(b) 138

(c) 13800

(d) 13

Q8. The power dissipated in the controlled source of the network shown below is

(a) 0 W

(b) 36 W

(c) 14 W

(d) 15 W

Q9. The impulse response of a second order under-damped system starting from rest is given by:

C(t)=12.5 e^(-6t) sin8t;t≥0

What is the value of natural frequency and damping factor of the system, respectively?

(a) 10 units and 0.6

(b) 10 units and 0.8

(c) 8 units and 0.6

(d) 8 units and 0.8

Q10. The power input to a 3-phase induction motor is 50 KW. If the stator losses are 800 W, then copper losses of rotor phase for 0.5 % slip will be:

(a) 492 W

(b) 246 W

(c) 200 W

(d) 100 W

SOLUTIONS

S5. Ans.(a)

Sol. Phase reversed of 180⁰ as compared to input occurs in the output of CE amplifier.

S6. Ans.(c)

Sol. A single phase, half-wave, controlled rectifier, V_avg=V_m/2π(1+cos〖α)〗

∵V_avg=400/2π(1+cos〖60⁰)=(400×3)/(2π ×2)〗=300/π

S7. Ans.(a)

Sol. meter constant(K)=N/kwh=(number of revolution)/energy

∴no. of revolution(N)=K × Energy= (200) ×((230*10*1*3))/1000=1380

S8. Ans.(c)

Sol. let the current flowing through the circuit=I

∴V_A=7I

KVL in given circuit: 36-15I-2VA-VA=0

⇒36-15I-3×(7I)=0

∴I=1 A

⇒V_A=7I=7 V

∴power dissipated in the controlled source=2VA I=2×7×1=14 W

S10. Ans.(b)

Sol. Air gap power or rotor input power (Pg )=stator input power-stator loss

∴Pg=50000-800=49200 W

Rotor copper loss (Pcu )=sPg=0.005×49200=246 W