This set of Basic Electrical Engineering Questions and Answers for Campus interviews focuses on “Addition and Subtraction of Sinusoidal Alternating Quantities”.

1. If two current phasors, having magnitude 5A and 10A intersect at an angle of 60 degrees, calculate the resultant current.

a) 5A

b) 10A

c) 25A

d) 20A

View Answer

Explanation: The resultant current can be found by using the parallelogram law of addition. Hence Iresultant= I1I2cos(theta), where theta is the angle between I1 and I2.

2. The instantaneous values of two alternating voltages are given as _________

v1=60sinθ and v2=40sin(θ − π/3). Find the instantaneous sum.

a) 87.2 sin(23.5°) V

b) 87.2 sin( 0.5°) V

c) 87.2 sin(-23.5°) V

d) 87.2 cos(23.5°) V

View Answer

Explanation: Horizontal component os v1= 60V

Vertical component of v1=0V

Horizontal component of v2=40cos60=20V

Vertical component of v2=-20sin60=-34.64V

Resultant horizontal component=80V

Resultant vertical component= -34.64V

Resultant v= 87.2V

tan(phi)=-34.64/80

phi= -23.5

Therefore sum= 87.2 sin( 23.5°) V.

3. The instantaneous values of two alternating voltages are given as:

v1=60sinθ and v2=40sin(θ − π/3). Find the instantaneous difference.

a) 53 sin(30.9°) V

b) 53 sin(40.9°) V

c) 53 cos(30.9°) V

d) 53 cos(40.9°) V

View Answer

Explanation: Horizontal component os v1= 60V

Vertical component of v1=0V

Horizontal component of v2=40cos60=20V

Vertical component of v2=-20sin60=-34.64V

Resultant horizontal component=40V

Resultant vertical component= 34.64V

Resultant v= 53

tan(phi)=34.64/40

phi= 40.9

Therefore sum= 53 sin (40.9°) V.

4. 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

View Answer

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.

5. 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

View Answer

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.

6. When one sine wave passes through the zero following the other, it is _________

a) Leading

b) Lagging

c) Neither leading nor lagging

d) Either leading or lagging

View Answer

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.

7. 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

View Answer

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.

8. For addition and subtraction of phasors, we use the _________ form.

a) Rectangular

b) Polar

c) Either rectangular or polar

d) Neither rectangular nor polar

View Answer

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.

9. For multiplication and division of phasors, we use ____________ form.

a) Rectangular

b) Polar

c) Either rectangular or polar

d) Neither rectangular nor polar

View Answer

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

10. The resultant of two alternating sinusoidal voltages or currents ca be found using ___________

a) Triangular law

b) Parallelogram law

c) Either triangular or parallelogram law

d) Neither triangular nor parallelogram law

View Answer

Explanation: The resultant current can be found by using the parallelogram law of addition. Where the magnitude is found by squaring the magnitudes, adding the squares and finding the square root of the sum and the theta is the angle between the two quantities.

**Sanfoundry Global Education & Learning Series – Basic Electrical Engineering.**

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