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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
(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 %
SOLUTIONS
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 %
