# Basic Electrical Engineering Questions and Answers – Representation of an Alternating Quantity by a Phasor

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This set of Basic Electrical Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Representation of an Alternating Quantity by a Phasor”.

1. For addition and subtraction of phasors, we use the _________ form.
a) Rectangular
b) Polar
c) Either rectangular or polar
d) Neither rectangular nor polar

Explanation: For addition and subtraction of phasors, we use the rectangular form because in the rectangular form we can only add the real part and the complex part separately to get the total value.

2. For multiplication and division of phasors, we use ____________ form.
a) Rectangular
b) Polar
c) Either rectangular or polar
d) Neither rectangular nor polar

Explanation: For multiplication and division of phasors, we use the polar form because in the polar form we just multiply or divide the values and add or subtract the angles.

3. If a voltage of 2+5j and another voltage of 3+ 6j flows through two different resistors, connected in series, in a circuit, find the total voltage in the circuit.
a) 2+5j V
b) 3+6j V
c) 5+11j V
d) 5+10j V

Explanation: The total voltage in the circuit is the sum of the two voltages where we add the real parts and imaginary parts separately.
Therefore, Vtotal= 5+11j V.
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4. Find the total current in the circuit if two currents of 4+5j flow in the circuit.
a) 4+5j A
b) 4A
c) 5A
d) 8+10j A

Explanation: The total current in the circuit is the sum of the two currents where we add the real parts and imaginary parts separately.
Therefore, Itotal= 8+10j A.

5. What is the correct expression of ω?
a) ω=2π
b) ω=2πf
c) ω=πf
d) ω=2f2

Explanation: The correct expression for ω is ω=2πf where f is the frequency of the alternating voltage or current.

6. Find the value of ω if the frequency is 5Hz?

Explanation: The expression for ω is ω=2*π*f.
Substituting the value of f from the question, we get ω=31.4 rad/s.

7. When one sine wave passes through the zero following the other, it is _________
b) Lagging

Explanation: The sine wave is said to lag because it passes though zero following the other, hence it crosses zero after the first wave, therefore it is said to lag.

8. A phasor has frozen at 30 degrees, find the value of the phase angle.
a) 30 degrees
b) 60 degrees
c) 120 degrees
d) 180 degrees

Explanation: The value of the phase angle is the value at which the phasor stops or freezes. Here, it freezes at 30 degree, hence the phase angle is 30 degrees.

9. The time axis of an AC phasor represents?
a) Time
b) Phase angle
c) Voltage
d) Current

Explanation: The time axis while measuring an AC sinusoidal voltage or current represents the phase angle when converting it to a phasor.

10. The length of the phasor represents?
a) Magnitude of the quantity
b) Direction of the quantity
c) Neither magnitude nor direction
d) Either magnitude or direction

Explanation: The length of the phasor arrow represents the magnitude of the quantity, whereas the angle between the phasor and the reference represents the phase angle.

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