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DFCCIL’21 EE: Daily Practices Quiz 20-Aug-2021

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               DFCCIL’21 EE: Daily Practices Quiz 20-Aug-2021

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

Q1. What is the relation between the thermal efficiency, electrical efficiency and overall efficiency for a steam power station?
(a) Overall efficiency = Thermal efficiency × electrical efficiency
(b) overall efficiency = (electrical efficiency)/(thermal efficiency)
(c) overall efficiency = (thermal efficiency)/(electrical efficiency)
(d) overal efficiency=(thermal efficiency+electrical efficiency)/2

Q2. What is emf induced in a1000 turn coil if 500 μWb of flux linking with it collapses in 1/10 second?
(a) 25 V
(b) 5 V
(c) 10 V
(d) 50 V

Q3. A circuit which does not contain any source of energy is a ____________ circuit.
(a) active
(b) bilateral
(c) unilateral
(d) passive

Q4. A cell of emf 2V supplies a current of 1.6 A when connected to a resistance of 1 Ω. What is the internal resistance of the cell?
(a) 1.25 Ω
(b) 0.25 Ω
(c) 1 Ω
(d) 0.4 Ω

Q5. The armature winding of an alternator is short pitched by 30 degrees. What is the coil span?
(a) 120 degrees
(b) 165 degrees
(c) 150 degrees
(d) 180 degrees

Q6. When a phase lag compensation is used in a system, then gain crossover frequency, bandwidth and natural frequency are respectively
(a) increased, increased, increased
(b) increased, increased, decreased
(c) increased, decreased, decreased
(d) decreased, decreased, decreased

SOLUTIONS
S1. Ans.(a)
Sol. Overall efficiency = Thermal efficiency × electrical efficiency

S2. Ans.(b)
Sol. e=N dϕ/dt=1000×((500×10^(-6))/(1/10))=5×10^6×10^(-6)=5 V

S3. Ans.(d)
Sol. Passive network does not contain any source of emf.

S4. Ans.(b)
Sol. 1+r=2/1.6 ; where r=internal resistance
∴r=1.25-1=0.25 Ω

S5. Ans.(c)
Sol. The armature winding of an alternator is short pitched by 30 degrees.
∴coil span=180⁰-30⁰=150⁰.
S6. Ans.(d)
Sol. Phase lag compensation decreases ω_gc, BW and ω_n

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