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DFCCIL’21 EE: Daily Practices Quiz 02-Sep-2021

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DFCCIL’21 EE: Daily Practices Quiz 02-Sep-2021

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

Q1. In the circuit shown, the current i is

(a) 2/5 A
(b) 4/5 A
(c) 6/5 A
(d) 7/5 A

Q2. In 220V, 50 Hz AC supply the rms value of AC voltage waveform is
(a) 220√2 V
(b) 220/√2 V
(c) 220 V
(d) None of these

Q3. Consider the following statements:
1. Resistor dissipates energy
2. Capacitor stores energy
3. Inductor dissipates energy
Which of the above is/are correct?
(a) 1, 2 and 3
(b) 1 and 3
(c) 3 alone
(d) 1 and 2

Q4. A 100mA meter has accuracy of +2%. Its accuracy while reading 50mA will be:
(a) +1%
(b) +2%
(c) +4%
(d) +20%

Q5. Which of the following statement is true?
(a) At higher voltage, cost of transmission is reduced
(b) At higher voltage, cost of transmission is increased
(c) Both a and b
(d) None of the above

Q6. In order to obtain higher efficiency for 3-phase induction motors, its slip should be:
(a) Low
(b) 1
(c) High
(d) Very high

SOLUTIONS
S1. Ans.(c)
Sol. By current division law, i=2×((2+1))/(2+(2+1) )=6/5 A.

S2. Ans.(c)
Sol. The voltage rating is the rms (root mean square) value of voltage.
Therefore, V_rms=220 V.

S3. Ans.(d)
Sol.
Resistance always dissipates power and does not store energy.
Capacitor stores energy in the form of electric field.
Inductor stores the energy in the form of magnetic field.

S4. Ans.(c)
Sol. Error = 100 mA ×(±2)/100= ±2mA
% Error = (±2mA)/50mA×100= ±4%.

S5. Ans.(a)
Sol. At higher voltage, volume of conductor is reduced. Area of conductor A ∝ 1/Vs² Where Vs = Supply voltage So that material requirement is reduced and hence cost of the material and transmission is reduced.

S6. Ans.(a)
Sol. for 3-phase induction motor, in order to obtain higher efficiency its slip should be low. i.e., rotor speed should be approx. equivalent to synchronous speed. (N≃N_S) .
Rotor efficiency =N_R/N_S or (1-S). So, if rotor speed is approx. equal to synchronous speed, then efficiency will be maximum. i.e., slip should be low.

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