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Multiple choice question for engineering

Set 1

1. Which of the following is not an expression power?
a) P=VI
b) P=I2R
c) P=V2/R
d) All of the mentioned

View Answer

Answer d [Reason:] Power is the product of voltage and current. Writing I in terms of V, we get P=V2/R and writing V in terms of I, we get P=I2r.

2. Which of the following statements are true?
a) Power is proportional to Voltage
b) Power is proportional to current
c) Neither of the statements are right
c) Both the statements are right

View Answer

Answer: d [Reason:] Power is proportional to both voltage and current. Hence both the options are right.

3. A 250V bulb passes a current of 0.3A. Calculate the power in the lamp.
a) 75W
b) 50W
c) 25W
d) 90W

View Answer

Answer: a [Reason:] Here, V = 250v and I = 0.3A. P=VI. Which implies that, P=250*0.3=75W.

4. Kilowatt-hour(kWh) is a unit of?
a) Current
b) Power
c) Energy
d) Resistance

View Answer

Answer: c [Reason:] Power is the energy per unit time. That is, P=E/t. If the unit of power is kW and the unit of time is hour, then the unit of energy=unit of power*unit of time=kWh.

5. Calculate the power in the 20 ohm resistance.
basic-electrical-engineering-questions-answers-power-q5
a) 2000kW
b) 2kW
c) 200kW
d) 2W

View Answer

Answer: b [Reason:] Here V = 200v and Resistance( R) = 20ohm. P=V2/R= 2002/20=2000W=2kW.

6. A current of 5A flows in a resistor of 2 ohm. Calculate the power in the resistor and the energy dissipated in 300 seconds.
a) 15kJ
b) 15000kJ
c)1500J
d) 15J

View Answer

Answer: a [Reason:] P=I2R =52*2=50W. E= Pt=50*300=15000J=15kJ.

7. Calculate the power across each 20 ohm resistance.
basic-electrical-engineering-questions-answers-power-q7
a) 1000W, 1000W
b) 500W, 500W
c) 1000kW, 1000kW
d) 500kW, 500kW

View Answer

Answer: b [Reason:] This is a series connected circuit hence the current across each resistance is the same. To find current: I=V/R=200/20=5A. To find power: P=I2R=52*20=500W. Since both the resistors have a resistance of 20 ohm, the power across both is the same.

8. Calculate the power across each 10 ohm resistance.
basic-electrical-engineering-questions-answers-power-q8
a) 1000kW, 1000kW
b) 1kW, 1kW
c) 100W, 100W
d) 100kW, 100kW

View Answer

Answer: b [Reason:] This parallel connected circuit, hence the voltage across each of the resistors are the same. P=V2/R= 1002/10=1000W=1kW. Since both the resistors receive the same amount of voltage, the Power in both are the same.

9. Calculate the work done in a resistor of 20 ohm carrying 5A of current in 3 hours.
a) 1.5J
b) 15J
c) 1.5kWh
d) 15kWh

View Answer

Answer: c [Reason:] To find power: P=I2R=52*20=500W=0.5kW. To find Work done: W=Pt=0.5*3=1.5kWh.

10. The SI unit of power is?
a) kW(kilo-watt)
b) J/s(joules per second)
c) Ws(watt-second)
d) J/h(joules per hour

View Answer

Answer: b [Reason:] Power = energy/time =J/s(joules per second). Hence the Si unit of Power is J/s.

Set 2

1. Quality factor is also known as _________
a) Voltage magnification
b) Current magnification
c) Resistance magnification
d) Impedance magnification

View Answer

Answer: a [Reason:] Quality factor is also known as voltage magnification because the voltage across the capacitor or inductor in resonance condition is equal to Q times the source voltage.

2. At resonance condition, voltage across the capacitor and inductor is _________ the source voltage.
a) Greater than
b) Less than
c) Equal to
d) Much less than

View Answer

Answer: a [Reason:] In resonance condition the voltage across the capacitor and inductor is greater than the source voltage because the voltage across the capacitor or inductor in resonance condition is equal to Q times the source voltage.

3. What is the voltage across the capacitor when the source voltage is 100V and the Q factor is 10.
a) 100V
b) 10V
c) 1000V
d) 0V

View Answer

Answer: c [Reason:] We know that voltage across the capacitor in resonance condition is equal to Q times the source voltage =10*100=1000V.

4. Find the Q factor when the voltage across the capacitor is 1000V and the source voltage is 100V.
a) 10
b) 20
c) 30
d) 40

View Answer

Answer: a [Reason:] We know that voltage across the capacitor in resonance condition is equal to Q times the source voltage. Vc=QV. Substituting the values from the given question, we get Q=10.

5. Find the source voltage when the voltage across the capacitor is 1000V and the Q factor is 10.
a) 10V
b) 200V
c) 100V
d) 90V

View Answer

Answer: c [Reason:] We know that voltage across the capacitor in resonance condition is equal to Q times the source voltage. Vc=QV. Substituting the values from the given question, we get V=100V.

6. What is the voltage across the inductor when the source voltage is 200V and the Q factor is 10.
a) 100V
b) 20V
c) 2000V
d) 0V

View Answer

Answer: c [Reason:] We know that voltage across the inductor in resonance condition is equal to Q times the source voltage =10*200=2000V.

7. Find the Q factor when the voltage across the indictor is 2000V and the source voltage is 100V.
a) 10
b) 20
c) 30
d) 40

View Answer

Answer: b [Reason:] We know that voltage across the inductor in resonance condition is equal to Q times the source voltage. VL=QV. Substituting the values from the given question, we get Q=20.

8. Find the source voltage when the voltage across the inductor is 2000V and the Q factor is 20.
a) 10V
b) 200V
c) 100V
d) 90V

View Answer

Answer: c [Reason:] We know that voltage across the inductor in resonance condition is equal to Q times the source voltage. VL=QV. Substituting the values from the given question, we get V=100V.

9. What happens to the voltage across the capacitor when the Q factor increases?
a) Increases
b) Decreases
c) Remains the same
d) Becomes zero

View Answer

Answer: a [Reason:] We know that voltage across the capacitor in resonance condition is equal to Q times the source voltage. Hence as the Q factor increases, the voltage across the capacitor also increases.

10. What happens to the voltage across the inductor when the Q factor decreases?
a) Increases
b) Decreases
c) Remains the same
d) Becomes zero

View Answer

Answer: b [Reason:] We know that voltage across the inductor in resonance condition is equal to Q times the source voltage. Hence as the Q factor decreases, the voltage across the inductor also decreases.

Set 3

1. Permeability of free space is also known as _________
a) Magnetic constant
b) Electric constant
c) Electrostatic constant
d) Magnetostatic constant

View Answer

Answer: a [Reason:] The permeability of free space is also known as magnetic constant. The permittivity of free space is the electrostatic constant.

2. A substance whose permeability is less than the permeability of free space is?
a) Diamagnetic
b) Paramagnetic
c) Ferromagnetic
d) Not a magnetic substance

View Answer

Answer: a [Reason:] A diamagnetic material creates a magnetic field opposing that of the external magnetic field and it repels the external magnetic field. Hence its permeability is less than that of free space.

3. Which, among the following, have negative susceptibility?
a) Diamagnetic
b) Paramagnetic
c) Ferromagnetic
d) Not a magnetic substance

View Answer

Answer: a [Reason:] Magnetic susceptibility is the degree of magnetisation of a material in response to the external magnetic field. Diamagnetic substances repel the magnetic field and hence have negative susceptibility.

4. Which, among the following, have positive susceptibility?
a) Diamagnetic
b) Paramagnetic
c) Ferromagnetic
d) Not a magnetic substance

View Answer

Answer: b [Reason:] Magnetic susceptibility is the degree of magnetisation of a material in response to the external magnetic field. Paramagnetic substances weakly attract to the magnetic field and hence have positive susceptibility.

5. A substance whose permeability is more than the permeability of free space is?
a) Diamagnetic
b) Paramagnetic
c) Ferromagnetic
d) Not a magnetic substance

View Answer

Answer: b [Reason:] A paramagnetic material creates a magnetic field which is weakly attracted to that of the external magnetic field. Hence its permeability is more than that of free space.

6. The unit for permeability of free space is?
a) Henry
b) Henry-m
c) Henry/m
d) Henry/m2

View Answer

Answer: c [Reason:] Magnetic permeability is the constant of proportionality between the magnetic flux density and magnetic field strength of a given medium. Hence it has units henry/m.

7. Which, among the following, is a correct expression for ∫0.
a) ∫0=BH
b) ∫0=B/H
c) ∫0=H/B
d) ∫0=BH2

View Answer

Answer: b [Reason:] Magnetic permeability is the constant of proportionality between the magnetic flux density and magnetic field strength of a given medium. Hence ∫0=B/H.

8. Calculate the magnetic flux density if the magnetic field strength is 2A/m.
a) 4*pi/10-7T
b) 8*pi/10-7T
c) 10*pi/10-7T
d) 12*pi/10-7T

View Answer

Answer: b [Reason:] We know that: ∫0=B/H Substituting the value of H from the question, we get B= 8*pi/10-7T.

9. Calculate the magnetic field strength if the magnetic flux density is 4*piT.
a) 10-7/16*pi2A/m
b) 10-7A/m
c) 107A/m
d) 10-7A

View Answer

Answer: c [Reason:] We know that: ∫0=B/H Substituting the value of B from the question, we get H = 107A/m.

10. Calculate the magnetic flux density if the magnetic field strength is 3A/m.
a) 4*pi/10-7T
b) 8*pi/10-7T
c) 10*pi/10-7T
d) 12*pi/10-7T

View Answer

Answer: d [Reason:] We know that: ∫0=B/H Substituting the value of H from the question, we get B= 12*pi/10-7T.

Set 4

1. What is the unit for relative permeability?
a) H-m
b) H/m
c) H2/m
d) No unit

View Answer

Answer: d [Reason:] Relative permeability is the ratio of permeability of the material to the permeability of free space. Since it is a ratio, it does not have any units.

2. Which of the following expressions is correct with respect to relative permeability?
a) B=∫r∫0/H
b) B=∫r∫0H
c) B=∫r/∫0H
d) B=∫r∫0/H2

View Answer

Answer: b [Reason:] For a non magnetic material: B=∫0H. Hence for a material having relative permeability ∫r, B=∫r∫0H.

3. A substance whose relative permeability is less than the permeability of free space is?
a) Diamagnetic
b) Paramagnetic
c) Ferromagnetic
d) Not a magnetic substance

View Answer

Answer: a [Reason:] A diamagnetic material creates a magnetic field opposing that of the external magnetic field and it repels the external magnetic field. Hence its relative permeability is less than that of the free space.

4. A substance whose relative permeability is more than the permeability of free space is?
a) Diamagnetic
b) Paramagnetic
c) Ferromagnetic
d) Not a magnetic substance

View Answer

Answer: b [Reason:] A paramagnetic material creates a magnetic field which is weakly attracted to that of the external magnetic field. Hence its permeability is more than that of free space.

5. Diamagnetic substances have relative permeability_____________
a) Greater than 1
b) Less than 1
c) Equal to 1
d) Zero

View Answer

Answer: b [Reason:] A diamagnetic material creates a magnetic field opposing that of the external magnetic field and it repels the external magnetic field. Hence it has relative permeability less than 1.

6. Paramagnetic substances have relative permeability_____________
a) Greater than 1
b) Less than 1
c) Equal to 1
d) Zero

View Answer

Answer: a [Reason:] A paramagnetic material creates a magnetic field which is weakly attracted to that of the external magnetic field. Hence it has relative permeability greater than 1.

7. As the temperature increases up to the Curie temperature, the relative susceptibility of ferromagnetic materials?
a) Increases
b) Decreases
c) Remains constant
d) Becomes zero

View Answer

Answer: a [Reason:] The susceptibility of ferromagnetic materials increases with the increase in temperature and then it decreases when the temperature goes beyond the Curie temperature.

8. As the temperature increases beyond the Curie temperature, the relative susceptibility of ferromagnetic materials?
a) Increases
b) Decreases
c) Remains constant
d) Becomes zero

View Answer

Answer: b [Reason:] The susceptibility of ferromagnetic materials increases with the increase in temperature and then it decreases when the temperature goes beyond the curie temperature.

9. Which, among the following, have positive susceptibility?
a) Diamagnetic
b) Paramagnetic
c) Ferromagnetic
d) Not a magnetic substance

View Answer

Answer: b [Reason:] Magnetic susceptibility is the degree of magnetisation of a material in response to the external magnetic field. Paramagnetic substances weakly attract to the magnetic field and hence have positive susceptibility.

10. Which, among the following, have negative susceptibility?
a) Diamagnetic
b) Paramagnetic
c) Ferromagnetic
d) Not a magnetic substance

View Answer

Answer: a [Reason:] Magnetic susceptibility is the degree of magnetisation of a material in response to the external magnetic field. Diamagnetic substances repel the magnetic field and hence have negative susceptibility.

Set 5

1. In order to obtain a high value for capacitance the permittivity of the dielectric medium should be?
a) Low
b) High
c) Zero
d) Unity

View Answer

Answer: b [Reason:] Form the expression: C=epsilon*A/d. From this expression, it is seen that capacitance is directly proportional to the permittivity, hence for capacitance value to be high, permittivity value should be high.

2. Find the capacitance of a capacitor whose area of cross section of the plates is 4m2 and distance of separation between the plates is 2m. The capacitor is placed in vacuum.
a) 1.77*10-11F
b) 1.34*10-11F
c) 2.33*10-11F
d) 5.65*10-11F

View Answer

Answer: a [Reason:] The expression for finding the value of capacitance is: C=epsilon*A/d. The medium is free space hence, epsilon= 8.85*10-12. Therefore, C=8.85*10-12*4/2= 1.77*10-12F.

3. What is relative permittivity?
a) Equal to absolute permittivity
b) Ratio of actual permittivity to absolute permittivity
c) Ratio of absolute permittivity to actual permittivity
d) Equal to actual permittivity

View Answer

Answer: b [Reason:] Relative permittivity is the ratio of actual permittivity to the relative permittivity of the medium. As the actual permittivity increases the relative permittivity also increases.

4. What happens to relative permittivity when actual permittivity decreases?
a) Increases
b) Decreases
c) Remains the same
d) Becomes zero

View Answer

Answer: b [Reason:] Relative permittivity is the ratio of actual permittivity to the relative permittivity of the medium. Relative permittivity is directly proportional to actual permittivity. Hence, as actual permittivity increases, relative permittivity also increases.

5. What is the relative permittivity when the actual permittivity is 4F/m?
a) 4.57*10-11
b) 4.57*1012
c) 4.57*1011
d) 4.57*10-12

View Answer

Answer: c [Reason:] Relative permittivity= Actual permittivity/ Absolute permittivity. Relative permittivity= 4/(8.85*10-12)= 4.57*1011.

6. What happens to absolute permittivity when relative permittivity increases?
a) Increases
b) Decreases
c) Remains the same
d) Becomes zero

View Answer

Answer: c [Reason:] Absolute permittivity does not depend on the value of relative permittivity. Absolute permittivity is the permittivity of free space and it is a constant value= 8.85*10-12F/m.

7. Calculate the actual permittivity of a medium whose relative permittivity is 5.
a) 4.43*10-11F/m
b) 4.43*10-12F/m
c) 4.43*1011F/m
d) 4.43*1012F/m

View Answer

Answer: a [Reason:] Actual permittivity= Relative permittivity*absolute permittivity. Actual permittivity= 5*8.85*10-12= 4.43*10-11F/m.

8. What is the unit for relative permittivity?
a) F/m
b) Fm
c) F/m2
d) No unit

View Answer

Answer: d [Reason:] Relative permittivity is the ratio of actual permittivity to the relative permittivity of the medium. Since it is a ratio, and we know that a ratio does not have any unit, relative permittivity does not have any unit.

9. Which, among the following, will be unity in free space?
a) Absolute permittivity
b) Relative permittivity
c) Actual permittivity
d) Both absolute and relative permittivity

View Answer

Answer: b [Reason:] Relative permittivity is constant for a particular medium. For air or free space ,it is unity. Absolute permittivity does not depend on the medium, its value is always constant=8.85*10-12F/m. Actual permittivity is the product of relative permittivity and absolute permittivity.

10. Which, among the following, do not have any unit?
a) Absolute permittivity
b) Relative permittivity
c) Actual permittivity
d) Both absolute and relative permittivity

View Answer

Answer: b [Reason:] Relative permittivity is the ratio of actual permittivity to the relative permittivity of the medium. Since it is a ratio, and we know that a ratio does not have any unit, relative permittivity does not have any unit.