AC circuits MCQ Question and Answer | ITI ELECTRICIAN

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ITI ELECTRICIAN | AC circuits MCQ

1.

What is the unit of susceptance?

1. Mho
2. Ohm
3. Henry
4. Farad

2.

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

1. 48 Ω
2. 42.5 Ω
3. 38.4 Ω
4. 26.6 Ω

3.

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

1. Increasing the inductance value
2. Reducing the capacitance value
3. Increasing the capacitance value
4. Increasing the value of resistance

4.

What is the formula to find 3 phase Reactive power (PR) if the line voltage is VL and line current is IL?

1. Pr = VL IL
2. Pr = 3 VL IL Cos θ
3. Pr = VL IL Sin θ
4. Pr = VL IL Cos θ

5.

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

1. Due to fluctuation of voltage
2. True power due to resistive load
3. Reactive power due to more inductive load
4. Reactive power due to more capacitive load

6.

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

1. No current will flow
2. The algebraic sum of current in 3 phases
3. The algebraic sum of current in 2 phases only
4. Lesser than the lowest current in any one of the phases

7.

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

1. 15.2 KVA
2. 11.5 KVA
3. 9.2 KVA
4. 5.3 KVA

8.

What will be the readings of two watt meters (W1& W2) in 3 phase power measurement, if the power factor is zero?

1. W1 & W2 both are positive reading
2. W1 is Positive and W2 is negative reading
3. W1 is equal to W2 but with opposite signs
4. Zero W1 is Positive reading, and W2 is negative reading

9.

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

1. 240V
2. 415V
3. 339.5V
4. 376.8V

10.

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

1. Pr = VI
2. Pr = √2 VI
3. Pr = VI cos θ
4. Pr = VI sin θ

11.

Calculate the impedance of the circuit R = 5Ω, XL= 36Ω and XC = 24 Ω.

1. 69 Ω
2. 65 Ω
3. 13 Ω
4. 12 Ω

12.

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

1. 90°
2. 120°
3. 180°
4. 270°

13.

What is the relation between the line voltage (VL) and phase voltage (Vp) in star connected system?

1. A 𝑉𝐿 = √3𝑉𝑃
2. B 𝑉𝐿 = 3𝑉𝑃
3. C 𝑉𝐿 = VP /√3
4. D 𝑉𝐿 = 𝑉𝑃/3

14.

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.

1. 8.5 A
2. 5.2 A
3. 4.5 A
4. 3.4 A

15.

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

1. 0
2. 1
3. 0.5
4. 0.8

16.

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

1. 0.8
2. 0.6
3. 0.5
4. 0.3

17.

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

1. #VALUE!
2. #VALUE!
3. #VALUE!
4. #VALUE!

18.

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

1. 0.5
2. 0.6
3. 0.7
4. 0.8

19.

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

1. 3.33 Mho
2. 0.33 Mho
3. 0.033 Mho
4. 0.003 Mho

20.

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

1. IL = IR - IC
2. IL = IR + IC
3. IL = IR2- IC2
4. IL = √(IR2- IC2)

21.

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

1. By connecting resistors in series
2. By connecting capacitors in series
3. By connecting inductors in series
4. By connecting capacitors in parallel

22.

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

1. IL = IP
2. IL = 3 IP
3. IL = √3 IP
4. IL = IP / √3

23.

What is the purpose of phase sequence meter?

1. To control the speed of 3 phase motor
2. To protect motor against short circuit fault
3. To indicate the incorrect phase sequence of 3 phase
4. To ensure the correct phase sequence of 3 phase system

24.

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.

1. 12.45 KVA
2. 57.50 KVA
3. 3.320 KVA
4. 7.188 KVA

25.

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?

1. 0.5
2. Zero
3. Unity
4. Below 0.5

26.

What is the formula for form factor(Kf)?

1. A Kf = 𝐸𝑓𝑓𝑒𝑐𝑡𝑖𝑣𝑒 𝑣𝑎𝑙𝑢𝑒 / 𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝑣𝑎𝑙𝑢𝑒
2. B Kf = 𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝑣𝑎𝑙𝑢𝑒 / 𝐸𝑓𝑓𝑒𝑐𝑡𝑖𝑣𝑒 𝑣𝑎𝑙𝑢𝑒
3. C Kf =𝐸𝑓𝑓𝑒𝑐𝑡𝑖𝑣𝑒 𝑣𝑎𝑙𝑢𝑒 / 𝑀𝑎𝑥𝑖𝑚𝑢𝑚 𝑣𝑎𝑙𝑢𝑒
4. D Kf = 𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝑣𝑎𝑙𝑢𝑒 / 𝑀𝑎𝑥𝑖𝑚𝑢𝑚 𝑣𝑎𝑙𝑢𝑒

27.

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

1. Resistance
2. Impedance
3. Admittance
4. Susceptance

28.

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

1. Pure resistive circuit
2. Resistance and inductance circuit
3. Resistance and capacitance circuit
4. Resistance, inductance and capacitance circuit

29.

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

1. 1 KVAR
2. 2 KVAR
3. 3 KVAR
4. 4 KVAR

30.

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

1. Inductive reactance (XL) is zero
2. Inductive reactance (XL) is equal to capacitive reactance (XC)
3. Inductive reactance (XL) is greater than capacitive reactance (XC)
4. Inductive reactance (XL) is less than capacitive reactance (XC)

31.

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

1. By interchanging the connections of input terminals
2. By disconnecting the connection of current coil in meter
3. By reversing the connection of pressure coil in meter
4. By reversing the pressure coil and current coil connection in meter

32.

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

1. 1
2. 1.11
3. 2.22
4. 4.44

33.

What is the reciprocal of inductance in AC parallel circuit?

1. Reactance
2. Admittance
3. Conductance
4. Susceptance

34.

What relationship is illustrated in between the current and voltage?

1. Current and voltage are “in phase”
2. Current and voltage are in out of phase
3. Current lags behind the voltage
4. Current leads ahead of the voltage

35.

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

1. W1 x 2
2. W1 only W1
3. W1 - W2
4. W1 + W2

36.

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

1. 3 wire star connected system
2. 4 wire star connected system
3. 3 wire delta connected system
4. 4 wire delta connected system

37.

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

1. 380 Volt
2. 400 Volt
3. 415 Volt
4. 440 Volt

38.

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

1. A Kf = 𝐸𝑓𝑓𝑒𝑐𝑡𝑖𝑣𝑒 𝑣𝑎𝑙𝑢𝑒 / 𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝑣𝑎𝑙𝑢𝑒
2. B Kf = 𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝑣𝑎𝑙𝑢𝑒 / 𝐸𝑓𝑓𝑒𝑐𝑡𝑖𝑣𝑒 𝑣𝑎𝑙𝑢𝑒
3. C Kf =𝐸𝑓𝑓𝑒𝑐𝑡𝑖𝑣𝑒 𝑣𝑎𝑙𝑢𝑒 / 𝑀𝑎𝑥𝑖𝑚𝑢𝑚 𝑣𝑎𝑙𝑢𝑒
4. D Kf = 𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝑣𝑎𝑙𝑢𝑒 / 𝑀𝑎𝑥𝑖𝑚𝑢𝑚 𝑣𝑎𝑙𝑢𝑒

39.

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

4. #VALUE!

40.

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

1. 0
2. 0.5
3. Unity
4. Less than 0.5 0.5

41.

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

1. 90°
2. 120°
3. 180°
4. 360°

42.

Which condition is called as resonance RLC circuit?

1. XL > XC
2. XC > XL
3. XL = XC
4. R < XL

43.

Which quantity is rotating at a constant angular velocity?

1. Scalar quantity
2. Vector quantity
3. Phasor quantity
4. Algebraic quantity