Coupling Coefficient MCQ [Free PDF] – Objective Question Answer for Coupling Coefficient Quiz

Electrical MCQ / May 31, 2022

21. In the figure given below, a 220 V 50 Hz supplies a 3 − phase balanced source. The pressure Coil (PC. and Current Coil (CC. of a wattmeter are connected to the load as shown. The wattmeter reading is _________

In the figure given below, a 220 V 50 Hz supplies a 3-phase balanced source. The pressure Coil (PC. and Current Coil

A. Zero
B. 1600 W
C. 242 W
D. 400 W

Answer: C

Watt − meter reading = Current through CC × Voltage across PC × cos (phase angle).
IBR = ICC = {220∠120°/100° = 2.2∠120°

VYB  = VPC  = 220∠ − 120°

w = 2.2∠120° × 220∠ − 120° × cos 240° = – 242 W.

 

22. In the Owen’s bridge shown in below figure, Z1  = 200∠60°, Z2  = 400∠ − 90°, Z3  = 300∠0°, Z4  = 400∠30°. Then,

In the Owen’s bridge shown in below figure, Z1 = 200∠60°, Z2 = 400∠-90°, Z3 = 300∠0°, Z4 = 400∠30°. Then,

A. Bridge is balanced with given impedance values
B. Bridge can be balanced, if Z4  = 600∠60°
C. Bridge can be balanced, if Z3  = 400∠0°
D. Bridge cannot be balanced with the given configuration

Answer: D

For Bridge to be balanced, the product of impedances of the opposite arm should be equal in magnitude as well as phase angle.

Here Z3 Z2 ≠ Z1 Z4 for whatever chosen value. Therefore the Bridge cannot be balanced.

 

23. In Maxwell’s capacitance bridge for calculating unknown inductance, the various values at balance are, R1  = 300 Ω, R2  = 700 Ω, R3  = 1500 Ω, C4  = 0.8 μF. The values of R1, L1 and Q factor, if the frequency is 1100 Hz are ____________

A. 240 Ω, 0.12 H, 3.14
B. 140 Ω, 0.168 H, 8.29
C. 140 Ω, 0.12 H, 5.92
D. 240 Ω, 0.36 H, 8.29

Answer: B

From Maxwell’s capacitance, we have

R1 = R2 R3/R4 = 300 ×700/1500 = 140 Ω

L1  = R2 R3 C4

= 300 × 700 × 0.8 × 10 − 6  = 0.168 H
∴ Q = ωL1/R1

= 2 × π × 1100 × 0.168/140 = 8.29.

 

24. In the figure below, the values of the resistance R1 and inductance L1 of a coil are to be calculated after the bridge is balanced. The values are _________________

In the figure below, the values of the resistance R1 and inductance L1 of a coil are to be calculated after the bridge is balanced.

A. 375 Ω and 75 mH
B. 75 Ω and 150 mH
C. 37.5 Ω and 75 mH
D. 75 Ω and 75 mH

Answer: A

Applying the usual balance condition relation,

Z1 Z4  = Z2 Z3

We have, (R1 + jL1 ω) \(\frac{R_4/jωC_4}{R_4+1/jωC_4}\) = R2 R3

Or, R1 R4 + jL1 ωR4  = R2 R3 + j R2 R3 R4 C4 ω

∴ R1 = 2000 × 750/4000 = 375 Ω

∴ L1  = 2000 × 750 × 0.5 × 10 − 6  = 75 mH.

 

25. The four arms of an AC bridge network are as follows:

Arm AB: unknown impedance
Arm BC: standard capacitor C2 of 1000pf
Arm CD: a non-inductive resistance of R of 100 Ω in parallel to a capacitor of 0.01 μF
Arm DA: a non-inductive resistance of 1000 Ω

The supply frequency is 50 Hz and connected across terminals B and D. If the bridge is balanced with the above value, determine the value of unknown Impedance.

A. 10 kΩ
B. 100 kΩ
C. 250 kΩ
D. 20 kΩ

Answer: A

For the balance conditions,

Z1 Z3 = Z2 Z4

1000 × \(\frac{1}{jω × 1000 × 10^{ − 12}} = (R + jX) \frac{100}{1 + j100 × ω × 0.01 × 10^{ − 6}}\)

\(\frac{10^{12}}{jω} = (R + jX) \left(\frac{100}{1 + jω + 10^{ − 6}}\right)\)

\(\frac{ − j 10^{10}}{ω}\) – 104 = R + jX

Comparing the real part, we get,

R = 10 kΩ.

 

26. What is the equivalent inductance when inductors are connected in series?

A. Sum of all the individual inductances
B. Product of all the individual inductances
C. Sum of the reciprocal of all the individual inductances
D. Product of the reciprocal of all the individual inductances

Answer: A

When inductances are connected in series, the equivalent inductance is equal to the sum of all the individual inductance values.

 

27. When inductances are connected in series, the equivalent inductance is ____________ the largest individual inductance.

A. Greater than
B. Less than
C. Equal to
D. Not related to

Answer: A

When inductances are connected in series, the equivalent inductance is equal to the sum of all the individual inductance values. Hence the equivalent inductance is greater than the largest individual inductance.

 

28. Three inductors having inductance values 3H, 4H, and 5H are connected in series, and calculate the equivalent inductance.

A. 10H
B. 12H
C. 3H
D. 5H

Answer: B

When inductances are connected in series, the equivalent inductance is equal to the sum of all the individual inductance values.

Hence Leq = L1+L2+L3 = 12H.

 

29. Calculate the equivalent inductance between A and B.

. Calculate the equivalent inductance between A and B.

A. 30H
B. 54H
C. 44H
D. 60H

Answer: C

The 4 inductors are connected in series, hence their equivalent inductance is:

Leq = L1+L2+L3+L4 = 44H.

 

30. When inductors are connected in series, the voltage across each inductor is _________

A. Equal
B. Different
C. Zero
D. Infinity

Answer: B

In a series circuit, the current across all elements remains the same and the total voltage of the circuit is the sum of the voltages across all the elements. The voltage across each inductor in series is different.

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