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WorksheetsUnit 6.Final Test.Eng Abedalrahman Alsheyab
Total questions: 40
Worksheet time: 29mins
An alternating current completes 100 cycles in 0.1 s. Its frequency is:
20 Hz
100 Hz
0.002 Hz
1 kHz
For the diagram shown below, which one of the following statements is true?
V2 leads V1.
V1 leads V2.
V1 lags V2.
V1 in Phase with V2.
Which one of the following statements is true?
In a capacitor, current lags voltage by 90°
In a resistor, voltage lags current by 90°
In a capacitor, voltage lags current by 90°
In a resistor, current lags voltage by 90°
What is the angular frequency (ω) of a waveform whose frequency is 60 Hz?
377 rad/s
188 rad/s
9.55 rad/s
120 rad/s
What will be the value of a capacitor in farads when it has a capacitive reactance of 200Ω and is connected to a 50Hz supply?
15 μF
15.92 μF
62.8 KF
10 KF
What is the expression for impedance in a series circuit derived from the right angled triangle?
Z2 = R2 – X2
Z2 = R2 ÷ X2
Z2 = R2 × X2
Z2 = R2 + X2
How are three phase voltages generated in one alternator?
By using three stator coils separated by 120º.
By using three stator coils separated by 60º.
By using three magnetic fields separated by 120º.
By using three magnetic fields separated by 60º.
The line currents in a three phase four-wire system are IBr, IBl and IG. What expression gives the current IN in the neutral conductor?
IN = IBr – IG + IBl
IN = IBr + IG – IBl
IN = IBr – IG – IBl
IN = IBr + IG + IBl
What is the relationship between line current IL and phase current IP in a delta connected load in a three-phase system?
Iline=IPhase
Iline =√3*Iphase
IPhase=√3*Iline
Iline =√2*Iphase
The time required for the values to rise and fall through one complete cycle is called the ------------ of the waveform.
period
frequency
maximum value
wavelength
What is the instantaneous value of this waveform at 20 µs?
approximately 7 V
approximately 3.5 V
approximately 1.5 V
approximately 4 V
To convert in the other direction (from rms values to peak values), use these equations:
Vp ≈ 1.414 × Vrms; Ip ≈ 1.414 × Irms
Vp ≈ 0.707 × Vrms; Ip ≈ 0.707 × Irms
Vp ≈ 2.414 × Vrms; Ip ≈ 2.414 × Irms
Vp ≈ 3.414 × Vrms; Ip ≈ 3.414 × Irms
One complete cycle of a sine wave is generated when a generator's rotor rotates through an angle of ----------.
360°
330°
300°
270°
For the diagram shown below, which one of the following statements is true?
Current lags voltage by 900 in phase
Voltage leads current by 00 in phase
Current leads voltage by 00 in phase
Voltage lags current by 900 in phase
Inductive reactance results in a current that
Leads the voltage by 90°
Is in phase with the voltage
Leads the voltage by π rad
Lags the voltage by π/2 rad
What is the inductive reactance of a 6.8 mH inductor when the current through it has a frequency of 96.2 kHz?
1.31 kΩ
243 µΩ
654 Ω
4.11 kΩ
In RLC circuit, VL and VC are ---------- “out-of-phase” and in opposition to each other.
360o
180o
270o
90o
In RLC circuit, If R is the resistance, XL is the inductive reactance and XC is the capacitive reactance, the impedance Z of the circuit is:
What is power factor in a circuit where the phase angle between current and voltage is ɸ?
Sin ɸ
Cos ɸ
Tan ɸ
ArcCos ɸ
What is the relationship for power factor in a single phase circuit?
Pf = I / V
Pf = kW / kVA
Pf = V / I
Pf = kVA / kW
What is one condition for resonance in a parallel ac circuit containing resistance (R) inductance (L) and capacitance (C)?
IL = IC
IL = IR
IL = 0
IC = 0
In the series RLC circuit, the resonant frequency ( ƒr ) occurs when:
XL = XC
XL > XC
XL < XC
XL ≠ XC
In the series RLC circuit, the resonant frequency ƒr is given by the formula:
What does the term "lag" means when voltage V1 lags V2 by 90 degrees?
V2 reaches its maximum value a half cycle after V1
V1 reaches its maximum value a half cycle after V2
V2 reaches its maximum value one quarter after V1
V1 reaches its maximum value one quarter after V2
What is the correct phase sequence of a three phase generator when V1 reaches maximum voltage before V2 and after V3?
V3, V1, V2
V1, V3, V2
V2, V1, V3
V3, V2, V1
What is the RMS value of a sinusoidal alternating voltage with a peak value of 100 V?
63.7 V
70.7 V
141.4 V
157.2 V
The elementary 3-phase 2-pole synchronous generator has a stator equipped with --------- coils displaced -------- from each other.
1 coil, 90o
2 coils, 120o
3 coils, 120o
4 coils, 150o
What is the relationship between phase voltage (VP) and line voltage (VL) in a star connected three-phase alternator?
VL = √3*VP
Vp = Z*VL
VL = Z*VP
Vp = √3*VL
What is the relationship between phase current IP and line current IL in a balanced star-connected load in a three phase circuit?
IL = IP
IL = IP ÷ 1.73
IL = IP + 1.73
IL = IP – 1.73
In the figure below, the value of the current passing in the neutral conductor is given by the equation:
IN= IR+IY−IB
IN= IR−IY+IB
IN= IR−IY−IB
IN= IR+IY+IB
In case of delta connection,
Line current = Phase current and Line voltage = √ 3 × Phase voltage
Line current = Phase current and Line voltage = phase voltage
Line voltage = Phase voltage and Line current = √3 × Phase current
Line current = Phase current and phase voltage = √3 × line voltage
Phase voltages of a star connected alternator are VR = 240∠ 0° V, VY = 240∠ -120° V & VB = 240 ∠ + 120° V. What is the phase sequence of the system ?
RYB.
RBY.
YBR.
BYR
What component can be added to large inductive loads to improve the 'power factor'?
Inductors
Reactors
Resistors
Capacitors
The current-carrying conductor arrangement shown in the figure below is
Single-phase 3-wire phase angle 0°
Two-phase 3-wire phase angle 90°
Three-phase 3-wire star connected
Three-phase 3-wire Delta connected
A 30 ohm resistance and a coil with inductance of 40 ohms are connected in series to a 100V 50Hz supply, where the power factor is CosƟ=0.6. Calculate the 'True power' for the circuit.
200 W
120 W
333.33 W
70 W
An A.C. circuit with a peak value of 100V and frequency of 50 Hz. Which of the following statements is false?
The periodic time is 20 ms
The r.m.s. value of the voltage is 70.7 V.
The Peak-to-Peak voltage value is 200 V
The Average voltage is 50 V.
Power Factor (Cos θ) =_________?
P/S
R/Z
The Cosine of angle between Current and voltage
All the Answers are correct.
Calculate the true power, reactive power and apparent power for a resistive/reactive load?
P=0 W, Q=169.25 VAR, S=238.73 VA
P=119.36 W, Q=119.99 VAR, S=169.25 VA
P=119.36 W, Q=238.73 VAR, S=238.73 VA
P=119.36 W, Q=119.99 VAR, S=119.99 VA
In the RLC circuit, the impedance Z equal:
12 Ω
17.3 Ω
19.4 Ω
21.7Ω
What component can be added to large inductive loads to improve the 'power factor'?
Inductors
Reactors
Resistors
Capacitors
