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DFCCIL’21 EE: Daily Practices Quiz 26-Aug-2021

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               DFCCIL’21 EE: Daily Practices Quiz 26-Aug-2021

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

Time : 8 min

Q1. An ideal current source has zero
(a) Internal conductance
(b) Internal resistance
(c) Voltage on no-load
(d) Ripple

Q2. Consider the non-inverting amplifier circuit of figure given below. The closed loop voltage gain is

DFCCIL 2021, dfccil electrical executive,_30.1
(a) 14
(b) -14
(c) 15
(d) 16

Q3. Which of the following instrument is free from hysteresis and eddy current loss?
(a) Moving iron instruments
(b) Electrostatic instruments
(c) PMMC instruments
(d) Dynamometer type instruments

Q4. Feedback control system is basically
(a) Band pass filter
(b) High pass filter
(c) Low pass filter
(d) Band stop filter

Q5. Slip of a 3-phase induction motor may be expressed as
(a) Rotor power input/rotor copper loss
(b) Rotor copper input/rotor core loss
(c) Rotor copper loss/rotor power input
(d) Rotor copper loss/ input power

Q6. A 40 KVA transformer has a core loss of 400 W and full-load copper loss of 800 W. The fraction of rated load at maximum efficiency is
(a) 50 %
(b) 62.3 %
(c) 100 %
(d) 70.7 %


S1. Ans.(a)
Sol. An ideal current source has infinite internal resistance, so zero internal conductance.

S2. Ans.(d)
Sol. A_V=V_0/V_i =(1+R_f/R_i )=(1+30/2)=16.

S3. Ans.(b)
Sol. Electrostatic instruments.

S4. Ans.(c)
Sol. Low pass filter is mainly as integral controller & it is used as the controller in the system so as to increase the accuracy by reducing or proper eliminating the steady state error of the control system.

S5. Ans.(c)
Sol. rotor power input= air gap power=(3I^2 R_2)/s
Rotor copper loss=3I^2 R_2
∴SLIP(s)=(3I^2 R_2)/((3I^2 R_2)/s)=(Rotor copper loss)/(rotor power input)

S6. Ans.(d)
Sol. η_max=√(P_i/P_cufl )=√(400/800) ×100=70.7 %

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