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# DFCCIL’21 EE: Daily Practices Quiz 10-Aug-2021

Each question carries 1 mark.
Negative marking: 1/4 mark
Total Questions: 06
Time: 08 min.

Q1. The starting torque of a wound rotor induction motor can be increased by adding:
(a) external capacitance to the rotor circuit
(b) external inductance to the rotor circuit
(c) a combination of inductance and capacitance to the rotor circuit
(d) external resistance to the rotor circuit

Q2. If three amplifiers having the same bandwidth are cascaded, the bandwidth of the resulting amplifier will be
(a) Better than that of each stage
(b) Worse than that of each stage
(c) Same as that of each stage
(d) None of the above

Q3. Two lamps 100 W and 40 W are connected in series across 230 V. Which of the following statement is correct?
(a) 40 W lamp will glow brighter
(b) 100 W lamp will glow brighter
(c) 40 W lamp will fuse
(d) Both lamps will glow equally bright

Q4. A GTO can be turned on by applying
(a) Positive gate signal
(b) Positive drain signal
(c) Positive source signal
(d) None of the above

Q5. The no load speed of DC series motor is
(a) very small
(b) medium
(c) very high
(d) small

Q6. A 8-pole lap-wound generator has 400 conductors; the e.m.f. induced per conductor being 5 V. The generated voltage of the generator is ………
(a) 60 V
(b) 1500 V
(c) 360 V
(d) 250 V

SOLUTIONS
S1. Ans.(d)
Sol. In an induction motor:
Generally, the initiation of these motors occurs when it draws full line voltage which is 6 to 7 times higher than the full load current. This high current can be controlled by external resistance connected in series with the rotor circuit.
the external resistance reduces high resistance as soon as the motor obtains normal speed and increases the starting torque of a motor. The tweaking of external resistance also aids in decreasing of rotor and stator current but improves the power factor of a motor.

S2. Ans.(b)
Sol. If N amplifiers having the same bandwidth(B) are cascaded, the bandwidth of the resulting amplifier will be: BW=B×√(2^(1/N)-1 )
So, the bandwidth of the resulting amplifier will decrease as the number of identical amplifier stages increases.

S3. Ans.(a)
Sol. Since both bulbs are rated at the same voltage, we can say that resistance of each bulb is inversely proportional to its rated power. Therefore, resistance of 40 W bulb (R40) is greater than the resistance of 100 W (R60) bulb.
Since lamps connected in series, the current flows through both the bulb are same.
Hence, for 40 W lamp due to higher resistance, heat dissipation will be more and will glow brighter.
NOTE:
For series connection lower power rating lamp will glow brighter.
For parallel connection, higher power rating lamp will glow brighter.

S4. Ans.(a)
Sol. Gate turn off (GTO), like an SCR is a device four-layer, three junction semiconductor devices with three external terminals (anode, cathode and gate). GTO can be turned on and off by positive pulse and negative pulse respectively to the gate terminal.

S5. Ans.(c)
Sol. The load-speed curve of DC series motor is shown below.

It is clear that the speed of the DC series motor at no load is very high. So, it is never stared at no load.

S6. Ans.(d)
Sol. For LAP connection; A=P=8
No of conductors per parallel path
=400/8=50
∴ E_g=50×5=250 V

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