Electrician 1st sem – NSQF – Module 6 – AC circuits mock Test

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Question 1 of 44

What is the main cause for below 0.5 lagging power factor in 3 phase system?

Reactive power due to more inductive load

Reactive power due to more capacitive load

True power due to resistive load

Due to fluctuation of voltage

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Question 1 of 44

Question 2 of 44

What is the formula to calculate the line current (I_L) of this single phase R - C parallel circuit?

I_L= I_R² + I_C²

I_L= I_R + I_C

I_L= √I_R² + I_C²

IL = IR - IC

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Question 2 of 44

Question 3 of 44

What is the resistance of the inductive coil takes 5A current across 240V, 50Hz supply at 0.8 power factor?

48 Ω

42.5Ω

38.4Ω

26.6Ω

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Question 3 of 44

Question 4 of 44

What is the maximum value of voltage for 240 volt RMS?

376.8V

415V

240V

339.5V

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Question 4 of 44

Question 5 of 44

In a 3 phase system, if the active power is 4 kw and the apparent power is 5 KVA, calculate the reactive power?

2 KVAR

1 KVAR

4 KVAR

3 KVAR

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Question 5 of 44

Question 6 of 44

What is the reciprocal of inductance in AC parallel circuit?

Reactance

Susceptance

Admittance

Conductance

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Question 6 of 44

Question 7 of 44

Which formula is used to calculate Form factor (K_f)?

K_f = Average value/Effective value

K_f= Maximum value/Effective value

K_f= Effective value/Average value

K_f = Maximum value/Average value

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Question 7 of 44

Question 8 of 44

What is the unit of susceptance?

Farad

Mho

Ohm

Henry

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Question 8 of 44

Question 9 of 44

Calculate the power factor of R.L.C circuit having resistance (R) = 15Ω, resultant reactance (X) = 20Ω connected across 240V /50Hz AC supply?

0.8

0.7

0.6

0.5

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Question 9 of 44

Question 10 of 44

10.

What is the formula to find 3 phase Reactive power (P_R) if the line voltage is 'V_L' and line current is 'I_L'?

P_r = 3V_L I_LCosθ

P_r = √3V_L I_LSinθ

P_r = V_L I_L

P_r = √3V_L I_LCosθ

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Question 10 of 44

Question 11 of 44

11.

What will be the readings of two watt meters (W_{1 &} W₂) in 3 phase power measurement, if the power factor is zero?

W_{1 &} W₂ both are positive reading

W₁ is equal to W₂ but with opposite signs

W_{1 &} is Positive and W ₂ is negative reading

Zero W₁is Positive reading, and W₂ is negative reading

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Question 11 of 44

Question 12 of 44

12.

Calculate the line current of the 3 phase 415V 50 HZ supply for the balanced load of 3000 watt at 0.8 power factor is connected in star.

3.4 A

4.5 A

8.5 A

5.2 A

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Question 12 of 44

Question 13 of 44

13.

How will you obtain positive reading in the wattmeter reads negative reading during 3-phase two wattmeter method?

By reversing the connection of pressure coil in meter

By reversing the pressure coil and current coil connection in meter

By disconnecting the connection of current coil in meter

By interchanging the connections of input terminals

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Question 13 of 44

Question 14 of 44

14.

Calculate the impedance of the circuit R = 5Ω, X_L = 36Ω and X_C = 24 Ω.

65 Ω

13 Ω

69 Ω

12 Ω

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Question 14 of 44

Question 15 of 44

15.

Calculate the apparent power in KVA of 3 phase 415V, 50 Hz, star system, if the line current (I _L ) is 16A at 0.8 power factor.

11.5 KVA

15.2 KVA

9.2 KVA

5.3 KVA

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Question 15 of 44

Question 16 of 44

16.

How the low power factor (P.F) can be improved in AC circuits?

By connecting capacitors in parallel

By connecting inductors in series

By connecting capacitors in series

By connecting resistors in series

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Question 16 of 44

Question 17 of 44

17.

What is the phase displacement between phases in a 3 phase circuit?

120°

90°

360°

180°

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Question 17 of 44

Question 18 of 44

18.

What relationship is illustrated in between the current and voltage?

Current and voltage are in out of phase

Current leads ahead of the voltage

Current lags behind the voltage

Current and voltage are "in phase"

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Question 18 of 44

Question 19 of 44

19.

What is the P.F if one of the wattmeters reading is zero and the other reads total power in 2 wattmeter method of 3 phase power measurement?

Unity

0.5

Zero

Below 0.5

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Question 19 of 44

Question 20 of 44

20.

What is the current in neutral conductor in 3 phase unbalanced load in star connected system?

Lesser than the lowest current in any one of the phases

The algebraic sum of current in 2 phases only

No current will flow

The algebraic sum of current in 3 phases

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Question 20 of 44

Question 21 of 44

21.

In which condition resonance will occur in R-L-C series circuit?

Inductive reactance (X_L) is zero

Inductive reactance (X_L) is less than capacitive reactance (X_C)

Inductive reactance (X_L) is equal to capacitive reactance (X_C)

Inductive reactance (X_L) is greater than capacitive reactance (X_C)

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Question 21 of 44

Question 22 of 44

22.

What is the condition for resonance in RLC series circuit? (Inductive reactance = 'X_L', Capacitive reactance = 'X_C')

X_L < X_C

X_L >√2 X_C

X_L = X_C

X_L > X_C

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Question 22 of 44

Question 23 of 44

23.

What is the power factor in a 3 phase power measurement of two wattmeters showing equal readings?

0.8

0.5

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Question 23 of 44

Question 24 of 44

24.

Which AC circuit contains the phase relation between voltage (V) and current (I)?

Resistance and inductance circuit

Pure resistive circuit

Resistance and capacitance circuit

Resistance, inductance and capacitance circuit

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Question 24 of 44

Question 25 of 44

25.

Which electrical term is defined as the total opposition to current in AC parallel circuit?

Impedance

Admittance

Resistance

Susceptance

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Question 25 of 44

Question 26 of 44

26.

What is the formula for Reactive Power (P_r ) in an AC circuit?

(P_r )= VI sin θ

(P_r )= VI

(P_r ) = VI cos θ

(P_r ) = √2 VI

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Question 26 of 44

Question 27 of 44

27.

Which condition is called as resonance RLC circuit?

R < X_L

X_L> X_C

X_C> X_L

X_L= X_C

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Question 27 of 44

Question 28 of 44

28.

How the resonance frequency (f_r) can be increased in A.C series circuit?

Increasing the value of resistance

Increasing the capacitance value

Increasing the inductance value

Reducing the capacitance value

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Question 28 of 44

Question 29 of 44

29.

What is the purpose of phase sequence meter?

To control the speed of 3 phase motor

To indicate the incorrect phase sequence of 3 phase

To ensure the correct phase sequence of 3 phase system

To protect motor against short circuit fault

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Question 29 of 44

Question 30 of 44

30.

What is the phase displacement in a single phase AC circuit?

180°

90°

270°

120°

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Question 30 of 44

Question 31 of 44

31.

What is the formula to calculate the three phase active power (P) if the line voltage (V_L) and line current is I_L and phase angle is 'θ'?

P = √ 3 V_L I_LSinθ

P = 3 V_L I_L Cosθ

P = 3 V_L I_L Sinθ

P = √ 3 V_L I_LCosθ

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Question 31 of 44

Question 32 of 44

32.

What is the power factor if one of the wattmeter gives negative reading in two wattmeter method of 3 phase power measurement?

Unity

Less than 0.5

0.5

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Question 32 of 44

Question 33 of 44

33.

What is the relation between the line current (I_L ) and phase current (I_P ) in delta connected system?

I_L = 3 I_P

I_L = I_P /√3

I_L = I_P

I_L = √3 I_P

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Question 33 of 44

Question 34 of 44

34.

Calculate the total power by two wattmeter (W₁ & W₂) method, if one of the wattmeter (W₂) reading is taken after reversing.

W₁x 2

W₁ only

W₁ - W₂

W₁ + W₂

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Question 34 of 44

Question 35 of 44

35.

Which formula is used to calculate the impedance (z) of a RLC series circuit?

Z = √R + (X_L ∼ X_C)

Z = √R² + (X_L ∼ X_C)²

Z = R + (XC - XL)

Z = R² + (X_L ∼ X_C)²

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Question 35 of 44

Question 36 of 44

36.

Calculate the apparent power of a star connected 3 phase load, if it is connected across 3 phase 415volt/50Hz supply at 0.8 p.f and the phase current is 10 Amps.

7.188 KVA

12.45 KVA

3.320 KVA

57.50 KVA

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Question 36 of 44

Question 37 of 44

37.

In which 3 phase system, the artificial neutral is required to measure the phase voltage?

3 wire star connected system

4 wire star connected system

3 wire delta connected system

4 wire delta connected system

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Question 37 of 44

Question 38 of 44

38.

What is the relation between the line voltage (V _L ) and phase voltage (V_p) in star connected system?

V_L = V_{p /}√3

V_L = √3V_p

V_L = 3V_p

V_L =V _p /3

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Question 38 of 44

Question 39 of 44

39.

Calculate the value admittance (Y) of the RLC parallel circuit connected across 240volts/50Hz AC supply and 8 Amp. Current is passed through it?

0.003 Mho

0.33 Mho

3.33 Mho

0.033 Mho

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Question 39 of 44

Question 40 of 44

40.

Calculate the power factor of coil having resistance of 24Ω, draws the current of 5A, at 240V/ 50Hz AC supply.

0.8

0.3

0.6

0.5

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Question 40 of 44

Question 41 of 44

41.

What is the line voltage in 3 phase system if the phase voltage is 240V?

440 Volt

415 Volt

400 Volt

380 Volt

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Question 41 of 44

Question 42 of 44

42.

What is the form factor (Kf) for sinusoidal AC?

1.00

1.11

4.44

2.22

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Question 42 of 44

Question 43 of 44

43.

What is the formula to calculate the impedance (Z) of the R.L.C series circuit, if the inductive reactance (X_L ) is less than capacitive rectance (X_C)?

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Question 43 of 44

Question 44 of 44

44.

Which quantity is rotating at a constant angular velocity?

Scalar quantity

Phasor quantity

Algebraic quantity

Vector quantity

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Question 44 of 44

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