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Multiple choice question for engineering

Set 1

1. Find the average value of current when the current that are equidistant are 4A, 5A and 6A.
a) 5A
b) 6A
c) 15A
d) 10A

Answer: a [Reason:] The average value of current is the sum of all the currents divided by the number of currents. Therefore average current= (5+4+6)/3=5A.

2. What is the type of current obtained by finding the square of the currents and then finding their average and then fining the square root?
a) RMS current
b) Average current
c) Instantaneous current
d) Total current

Answer: a [Reason:] RMS stands for Root Mean Square. This value of current is obtained by squaring all the current values, finding the average and then finding the square root.

3. For a rectangular wave, average current is ______ rms current.
a) Greater than
b) Less than
c) Equal to
d) Not related

Answer: c [Reason:] The rms value is always greater than the average except for a rectangular wave, in which the heating effect remains constant so that the average and the rms values are the same.

4. __________ current is found by dividing the area enclosed by the half cycle by the length of the base of the half cycle.
a) RMS current
b) Average current
c) Instantaneous current
d) Total current

Answer: b [Reason:] The average value of current is the sum of all the currents divided by the number of currents. Hence it can also be found by dividing the area enclosed by the half cycle by the length of the base of the half cycle.

5. Average value of current over a half cycle is _________
a) 0.67Im
b) 0.33Im
c) 6.7Im
d) 3.3Im

Answer: a [Reason:] Integrating idθ in the interval from 0 to pi (since we are finding the average current over one half cycle) , we get i=0.61Im.

6. What is the correct expression for the rms value of current?
a) Irms=Im/2
b) Irms=Im/√2
c) Irms=Im/4
d) Irms=Im

Answer: b [Reason:] The correct expression for the rms value of current is Irms= Im/√2, where Im is the maximum or peak value of the current.

7. If Im is the maximum value of a sinusoidal voltage, what is the instantaneous value?
a) i=Im/2
b) i=Imsinθ
c) i=Imcosθ
d) i=Im

Answer: b [Reason:] The instantaneous value of a sinusoidal varying current is i=Imsinθ, where theta is the angle from instant of zero current.

8. What is the correct expression for form factor?
a) I*Iav
b) I/Iav
c) I+Iav
d) I-Iav

Answer: b [Reason:] The correct expression for form factor is ki=I/Iav, where I is the rms value of the current and Iav is the average current.

9. For a direct current, the rms current is ________ the mean current.
a) Greater than
b) Less than
c) Equal to
d) Not related to

Answer: c [Reason:] For a direct current, that is, a non-sinusoidal current, the mean current value is same as that of the rms current.

10. For a direct voltage, the rms voltage is ________ the mean voltage.
a) Greater than
b) Less than
c) Equal to
d) Not related to

Answer: c [Reason:] For a direct current, that is, a non-sinusoidal current, the mean voltage value is same as that of the rms voltage.

Set 2

1.The SI unit for bandwidth is?
a) Hz
b) Watt
c) kHz
d) kW

Answer: a [Reason:] The SI unit for bandwidth is Hz. Hertz is the SI unit because bandwidth is basically frequency and the unit for frequency is Hz.

2. At bandwidth frequency range, the value of the current I is?
a) I=Im/2
b) I=Im2
c) I=Im
d) I=Im/√2

Answer: d [Reason:] At the bandwidth frequency range, the value of the current is equal to the maximum value of current divided by √2.

3. At bandwidth frequency range, the value of the voltage V is?
a) V=Vm/2
b) V=Vm2
c) V=Vm
d) V=Vm/√2

Answer: d [Reason:] At the bandwidth frequency range, the value of the voltage is equal to the maximum value of voltage divided by √2.

4. At resonance, bandwidth includes the frequency range that allows _____ percent of the maximum current to flow.
a) 33.33
b) 66.67
c) 50
d) 70.7

Answer: d [Reason:] At resonance, bandwidth includes the frequency range that allows 70.2 percent of the maximum current to flow. This is because at the bandwidth frequency range, the value of the current is equal to the maximum value of current divided by √2.

5. At resonance, bandwidth includes the frequency range that allows _____ percent of the maximum voltage to flow.
a) 33.33
b) 66.67
c) 50
d) 70.7

Answer: d [Reason:] At resonance, bandwidth includes the frequency range that allows 70.2 percent of the maximum voltage to flow. This is because at the bandwidth frequency range, the value of the voltage is equal to the maximum value of voltage divided by √2.

6. Find the value of current when the maximum value of current is 50A in the bandwidth range.
a) 56.65A
b) 35.36A
c) 45.34A
d) 78.76A

Answer: b [Reason:] At the bandwidth frequency range, the value of the current is equal to the maximum value of current divided by √2. Hence I =50/√2= 35.36A.

7. Find the value of voltage when the maximum value of voltage is 100V.
a) 56.65A
b) 35.36A
c) 45.34A
d) 70.72A

Answer: b [Reason:] At the bandwidth frequency range, the value of the voltage is equal to the maximum value of voltage divided by √2. Hence V =100/√2= 70.72V.

8. If the resonant frequency in a series RLC circuit is 50kHz along with a bandwidth of 5kHz, find the quality factor.
a) 5
b) 50
c) 10
d) 500

Answer: c [Reason:] We know that Quality factor is equal to the resonant frequency divided by the bandwidth. Substituting the values from the given question, we get Q=10.

9. What happens to the bandwidth frequency range when the quality factor increases?
a) Increases
b) Decreases
c) Remains the same
d) Becomes zero

Answer: b [Reason:] The bandwidth frequency range decreases as the Q factor increases because the bandwidth is inversely proportional to the Q factor.

10. Find the bandwidth when the resonant frequency is 50kHz and the Q factor is 10.
a) 5kHz
b) 50kHz
c) 10kHz
d) 500kHz

Answer: a [Reason:] We know that Quality factor is equal to the resonant frequency divided by the bandwidth. Substituting the values from the given question, we get BW= 5kHz.

Set 3

1. In a parallel circuit, we consider _____________ instead of impedance.
a) Resistance
b) Capacitance
c) Inductance

2. In a parallel circuit, we consider instead of __________
a) Resistance
b) Capacitance
c) Inductance
d) Impedance

3. Which, among the following is the correct expression for impedance?
a) Z=Y
b) Z=1/Y
c) Z=Y2
d) Z=1/Y2

Answer: b [Reason:] We know that impedance is the reciprocal of admittance, hence the correct expression for impedance is: Z=1/Y.

4. Which, among the following is the correct expression for admittance?
a) Y=Z
b) Y=1/Z
c) Y=Z2
d) Y=1/Z2

Answer: b [Reason:] We know that admittance is the reciprocal of impedance, hence the correct expression for admittance is: Y=1/Z.

5. What is the unit of admittance?
a) ohm
b) henry
d) ohm-1

Answer: d [Reason:] The unit for admittance is ohm-1 because the unit of impedance is ohm and admittance is the reciprocal of impedance.

6. As the impedance increases, the admittance ____________
a) Increases
b) Decreases
c) Remains the same
d) Becomes zero

7. if the impedance of a system is 4 ohm, calculate its admittance.
a) 0.25 ohm-1
b) 4 ohm-1
c) 25 ohm-1
d) 0.4 ohm-1

Answer: a [Reason:] We know that: Y=1/Z. Substituting the value of Z from the question, we get Y= 0.25 ohm-1.

8. The admittance of a system is 10 ohm^-1, calculate its impedance.
a) 10 ohm
b) 0.1 ohm
c) 1 ohm
d) 1.1 ohm

Answer: b [Reason:] We know that: Z=1/Y. Substituting the value of Y from the question, we get Z= 0.1 ohm.

9. If two bulbs are connected in parallel and one bulb blows out, what happens to the other bulb?
a) The other bulb blows out as well
b) The other bulb continues to glow with the same brightness
c) The other bulb glows with increased brightness
d) The other bulb stops glowing

Answer: b [Reason:] In a parallel circuit, if one bulb blows out, it acts as an open circuit. Current does not flow in that branch but it continues to flow in the other branch hence the bulb continues to glow.

10. In A parallel circuit, with any number of impedances, The voltage across each impedance is?
a) The same for all impedances
b) Is divided equally among all impedances
c) Is divided proportionally across all impedances
d) Is zero for all impedances

Answer: a [Reason:] In parallel circuits, the current across the circuits vary whereas the voltage remains the same.

Set 4

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

Answer: c [Reason:] 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

Answer: a [Reason:] 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

Answer: b [Reason:] 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

Answer: c [Reason:] 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

Answer: d [Reason:] 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 _________
b) Lagging

Answer: b [Reason:] 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

Answer: a [Reason:] 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

Answer: a [Reason:] 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

Answer: a [Reason:] 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

Answer: b [Reason:] 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.

Set 5

1. Power factor of a circuit can be improved by placing which, among the following, in a circuit?
a) Inductor
b) Capacitor
c) Resistor
d) Switch

Answer: b [Reason:] Raising the power factor on a kW load decreases its kVA. Hence, by adding a capacitor in a circuit, an additional kW load can can be added to the system without altering the kVA. Hence, the power factor is improved.

2. When the supply frequency increases, what happens to the capacitive reactance in the circuit?
a) Increases
b) Decreases
c) Remains the same
d) Becomes zero

Answer: b [Reason:] The expression for capacitive reactance is: Xc=1/(2*pi*f*C). This relation shows that frequency is inversely related to capacitive reactance. Hence, as supply frequency increases, the capacitive reactance increases.

3. Calculate the time constant of a series RC circuit consisting of a 100microF capacitor in series with a 100ohm resistor.
a) 0.1 sec
b) 0.1 msec
c) 0.01 sec
d) 0.01 msec

Answer: c [Reason:] The time constant of a RC circuit= R*C= 100*10-6*100=0.01 sec.

4. Capacitors charge and discharge in __________ manner.
a) Linear
b) Constant
c) Square
d) Exponential

Answer: d [Reason:] Capacitors charge and discharge in an exponential manner because of the relation: C=1/(2*pi*f*Xc).

5. Air has a dielectric constant of ___________
a) Unity
b) Zero
c) Infinity

Answer: a [Reason:] Dielectris constant of air is the same as that of vacuum which is equal to unity. Dielctric constant of air is taken as the reference to measure the dielectric constant of all other materials.

6. What is the value of capacitance of a capacitor which has a voltage of 4V and ha 8C of charge.
a) 2F
b) 4F
c) 6F
d) 8F

Answer: a [Reason:] Q is directly proportional to V. The constant of proportionality in this case is C, that is, the capacitance. Hence Q=CV. From the relation, C=Q/V= 8/4=2F.

7. Unit of capacitance is___________
a) Volts
c) Henry
d) Newton

Answer: b [Reason:] Volts is the unit of voltage, Henry for inductance and Newton for force. Hence the unit for capacitance is Farad.

8. What will happen to the capacitor when the source is removed?
a) It will not remain in its charged state
b) It will remain in its charged state
c) It will start discharging
d) It will become zero

Answer: b [Reason:] As soon as the source is removed, the capacitor does not start discharging it remains in the same charged state.

9. Which among the following equations is incorrect?
a) Q=CV
b) Q=C/V
c) V=Q/C
d) C=Q/V