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Multiple choice question for engineering

Set 1

1. For high frequencies, capacitor acts as _______
a) Open circuit
b) Short circuit
c) Amplifier
d) Rectifier

View Answer

Answer: b [Reason:] Capacitive impedance is inversely proportional to frequency. Hence at very high frequencies, the impedance is almost equal to zero, hence it acts as a short circuit and there is no voltage across it.

2. For very low frequencies, capacitor acts as _______
a) Open circuit
b) Short circuit
c) Amplifier
d) Rectifier

View Answer

Answer: a [Reason:] Capacitive impedance is inversely proportional to frequency. Hence at very low frequencies the impedance is almost infinity and hence acts as an open circuit and no current flows through it.

3. A capacitor consists of___________
a) Two conductors
b) Two semiconductors
c) Two dielectrics
d) Two insulators

View Answer

Answer: a [Reason:] A capacitor consists of two conductors connected in parallel to each other so that it can store charge in between the plates.

4. Capacitor preferred when there is high frequency in the circuits is ______
a) Electrolyte capacitor
b) Mica capacitor
c) Air capacitor
d) Glass capacitor

View Answer

Answer: b [Reason:] Mica capacitors are preferred for high frequency circuits because they have low ohmic losses and less reactance.

5. Capacitance increases with ______
a) Increase in plate area
b) Decrease in plate area
c) Increase in distance between the plates
d) Increase in density of the material

View Answer

Answer: a [Reason:] Capacitance is directly proportional to plate area. Hence as plate area increases, the capacitance also increases.

6. Capacitance decreases with _________
a) Increase in distance between the plates
b) Decrease in plate area
c) Decrease in distance between the plates
d) Increase in density of the material

View Answer

Answer: c [Reason:] Capacitance is inversely proportional to the distance between the two parallel plates. Hence, as the distance between the plates decreases, the capacitance increases.

7. 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

View Answer

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.

8. What is the value of capacitance of a capacitor which has a voltage of 4V and ha 16C of charge.
a) 2F
b) 4F
c) 6F
d) 8F

View Answer

Answer: b [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= 16/4=4F.

9. Unit of capacitance is __________
a) Volts
b) Farad
c) Henry
d) Newton

View Answer

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

10. 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

View Answer

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

Set 2

1. Which is the correct expression for capacitance of a multi plate capacitor?
a) C=absolute permittivity*A/d
b) C=Actual permittivity*(n-1)*A/d
c) C=Actual permittivity*(n)*A/d
d) Actual permittivity*(n+1)*A/d

View Answer

Answer: b [Reason:] The correct expression is: C=Actual permittivity*(n-1)*A/d. Where, n=number of plates, A=area of cross section of the plates, d=distance of separation between the plates.

2. What happens to the capacitance of a multi plate capacitor when the area of cross section of the plate decreases?
a) Increases
b) Decreases
c) Remains constant
d) Becomes zero

View Answer

Answer: b [Reason:] When the area of cross section decreases, the capacitance also decreases since it is related by the formula C=Actual permittivity*(n-1)*A/d. Here, we can see that the capacitance is directly proportional to the area of cross section.

3. What happens to the capacitance of a multi plate capacitor when the distance of separation between the plate increases?
a) Increases
b) Decreases
c) Remains constant
d) Becomes zero

View Answer

Answer: b [Reason:] When the distance of separation between the plates decreases, the capacitance also decreases since it is related by the formula C=Actual permittivity*(n-1)*A/d. Here, we can see that the capacitance is inversely proportional to the distance of separation.

4. What happens to the capacitance of a multi plate capacitor when the number of plates increases?
a) Increases
b) Decreases
c) Remains constant
d) Becomes zero

View Answer

Answer: a [Reason:] When the number of capacitors increases, the capacitance also increases since it is related by the formula C=Actual permittivity*(n-1)*A/d. Here, we can see that the capacitance is directly proportional to the number of capacitors.

5. Find the capacitance of a multi plate capacitor whose actual permittivity= 5F/m, n=3, A=4m2and d=2m.
a) 10F
b) 20F
c) 30F
d) 40F

View Answer

Answer: b [Reason:] The formula for capacitance of a multi plate capacitor: C=Actual permittivity*(n-1)*A/d. Thus, C=5*(3-1)*4/2= 20F.

6. Find the capacitance of a multi plate capacitor whose relative permittivity=5, n=3, A=4m2 and d=2m.
a) 1.77*10-10 F
b) 1.77*1010 F
c) 1.77*10-11 F
d) 1.77*1011 F

View Answer

Answer: a [Reason:] The formula for capacitance of a multi plate capacitor: C=Relative permittivity*absolute permittivity*(n-1)*A/d. C= 5*8.85*10-12*(3-1)*4/2=1.77*10-10.

7. Find the number of plates in the multi plate capacitor having C=20F absolute permittivity=5F/m, A=4m2 and d=2m.
a) 1
b) 2
c) 3
d) 4

View Answer

Answer: c [Reason:] The formula for capacitance of a multi plate capacitor: C=Actual permittivity*(n-1)*A/d. Substituting the given values in the equation, we get n=3.

8. Calculate the distance between the plates of the capacitor having C=20F, actual permittivity=F/m
n=3 and A=4m2.
a) 1m
b) 2m
c) 3m
d) 4m

View Answer

Answer: b [Reason:] The formula for capacitance of a multi plate capacitor: C=Actual permittivity*(n-1)*A/d. Substituting the given values in the equation, we get d=2m.

9. Calculate the area of cross section of the multi plate capacitor having C=20F, actual permittivity=F/m n=3 and d=2m.
a) 1m
b) 2m
c) 3m
d) 4m

View Answer

Answer: d [Reason:] The formula for capacitance of a multi plate capacitor: C=Actual permittivity*(n-1)*A/d. Substituting the given values in the equation, we get A=4m2.

10. Calculate the number of plates in the multi plate capacitor having C=1.77*10-10F relative permittivity=5, A=4m2 and d=2m.
a) 1m
b) 2m
c) 3m
d) 4m

View Answer

Answer: c [Reason:] The formula for capacitance of a multi plate capacitor: C=Relative permittivity*absolute permittivity*(n-1)*A/d. Substituting the given values in the equation, we get n=3.

Set 3

1. What is the relation between current and voltage in a capacitor?
a) I=1/C*integral(Vdt)
b) I=CdV/dt
c) I=1/CdV/dt
d) I=Ct

View Answer

Answer: b [Reason:] Current=rate of change of charge=> I=dQ/dt. Q=CV, hence I=CdQ/dt.

2. If 2V is supplied to a 3F capacitor, calculate the chance stored in the capacitor.
a) 1.5C
b) 6C
c) 2C
d) 3C

View Answer

Answer: b [Reason:] Q is directly proportional to V. The constant of proportionality in this case is C, that is, the capacitance. Hence Q=CV. Q=3*2=6C.

3. Calculate the current in the capacitor having 2V supply voltage and 3F capacitance in 2seconds.
a) 2A
b) 5A
c) 6A
d) 3A

View Answer

Answer: d [Reason:] Q is directly proportional to V. The constant of proportionality in this case is C, that is, the capacitance. Hence Q=CV. Q=3*2=6C. I=Q/t= 6/2=3A.

4. A 4microF capacitor is charged to 120V, the charge in the capacitor would be?
a) 480C
b) 480microC
c) 30C
d) 30microC

View Answer

Answer: b [Reason:] Q is directly proportional to V. The constant of proportionality in this case is C, that is, the capacitance. Hence Q=CV. Q=4*120=480microC.

5. For high frequencies, capacitor acts as _________
a) Open circuit
b) Short circuit
c) Amplifier
d) Rectifier

View Answer

Answer: b [Reason:] Capacitive impedance is inversely proportional to frequency. Hence at very high frequencies, the impedance is almost equal to zero, hence it acts as a short circuit and there is no voltage across it.

6. For very low frequencies, capacitor acts as ________
a) Open circuit
b) Short circuit
c) Amplifier
d) Rectifier

View Answer

Answer: a [Reason:] Capacitive impedance is inversely proportional to frequency. Hence at very low frequencies the impedance is almost infinity and hence acts as an open circuit and no current flows through it.

7. A capacitor consists of_________
a) Two conductors
b) Two semiconductors
c) Two dielectrics
d) Two insulators

View Answer

Answer: a [Reason:] A capacitor consists of two conductors connected in parallel to each other so that it can store charge in between the plates.

8. Capacitor preferred when there is high frequency in the circuits is __________
a) Electrolyte capacitor
b) Mica capacitor
c) Air capacitor
d) Glass capacitor

View Answer

Answer: b [Reason:] Mica capacitors are preferred for high frequency circuits because they have low ohmic losses and less reactance.

9. Capacitance increases with ________
a) Increase in plate area
b) Decrease in plate area
c) Increase in distance between the plates
d) Increase in density of the material

View Answer

Answer: a [Reason:] Capacitance is directly proportional to plate area. Hence as plate area increases, the capacitance also increases.

10. Capacitance decreases with __________
a) Increase in distance between the plates
b) Decrease in plate area
c) Decrease in distance between the plates
d) Increase in density of the material

View Answer

Answer: c [Reason:] Capacitance is inversely proportional to the distance between the two parallel plates. Hence, as the distance between the plate decreases, the capacitance increases.

Set 4

1. What is the total capacitance when three capacitors, C1, C2 and C3 are connected in parallel?
a) C1/(C2+C3)
b) C1+C2+C3
c) C2/(C1+C3)
d) 1/C1+1/C2+1/C3

View Answer

Answer: b [Reason:] When capacitors are connected in parallel, the total capacitance is equal to the sum of the capacitance of each of the capacitors. Hence Ctotal=C1+C2+C3.

2. Calculate the total capacitance.
basic-electrical-engineering-questions-answers-capacitors-parallel-q2
a) 10F
b) 15F
c) 13F
d) 20F

View Answer

Answer: c [Reason:] The equivalent capacitance when capacitors are connected in parallel is the sum of all the capacitors= 1+2+10= 13F.

3. Calculate the voltage across AB if the total change stored in the combination is 13C.
basic-electrical-engineering-questions-answers-capacitors-parallel-q2
a) 1V
b) 2V
c) 3V
d) 4V

View Answer

Answer: a [Reason:] The equivalent capacitance when capacitors are connected in parallel is the sum of all the capacitors= 1+2+10= 13F. V=Q/C= 13/13=1V.

4. Calculate the charge in the 2F capacitor.
basic-electrical-engineering-questions-answers-capacitors-parallel-q4
a) 200C
b) 100C
c) 300C
d) 400C

View Answer

Answer: a [Reason:] Since the capacitors are connected in parallel, the voltage across each is the same, it does not get divided. Q=CV= 2*100=200C.

5. Calculate the charge in the 1F capacitor.
basic-electrical-engineering-questions-answers-capacitors-parallel-q4
a) 200C
b) 100C
c) 300C
d) 400C

View Answer

Answer: b [Reason:] Since the capacitors are connected in parallel, the voltage across each is the same, it does not get divided. Q=CV= 1*100=100C.

6. Calculate the total charge of the system.
basic-electrical-engineering-questions-answers-capacitors-parallel-q4
a) 200C
b) 100C
c) 300C
d) 400C

View Answer

Answer: c [Reason:] The equivalent capacitance when capacitors are connected in parallel is the sum of all the capacitors=1+2=3F. Q=CV= 3*100= 300V.

7. When capacitors are connected in parallel, the total capacitance is always __________ the individual capacitance values.
a) Greater than
b) Less than
c) Equal to
d) Cannot be determined

View Answer

Answer: a [Reason:] When capacitors are connected in parallel, the total capacitance is equal to the sum of the capacitance of each of the capacitors. Hence Ctotal=C1+C2+C3. Since it is the sum of all the capacitance values, total capacitance is greater the the individual capacitance values.

8. When capacitors are connected in parallel, what happens to the effective plate area?
a) Increases
b) Decreases
c) Remains the same
d) Becomes zero

View Answer

Answer: a [Reason:] When capacitors are connected in parallel, the top plates of each of the capacitors are connected together while the bottom plates are connected to each other. This effectively increases the top plate area and the bottom plate area.

9. Three capacitors having capacitance equal to 2F, 4F and 6F are connected in parallel. Calculate the effective parallel.
a) 10F
b) 11F
c) 12F
d) 13F

View Answer

Answer: c [Reason:] When capacitors are connected in parallel, the total capacitance is equal to the sum of the capacitance of each of the capacitors. Hence Ctotal=C1+C2+C3= 2+4+6=12F.

10. Two capacitors having capacitance value 4F, three capacitors having capacitance value 2F and 5 capacitors having capacitance value 1F are connected in parallel, calculate the equivalent capacitance.
a) 20F
b) 19F
c) 18F
d) 17F

View Answer

Answer: b [Reason:] When capacitors are connected in parallel, the total capacitance is equal to the sum of the capacitance of each of the capacitors. Hence Ctotal=4+4+2+2+2+1+1+1+1+1=19F.

Set 5

1. What is the total capacitance when two capacitors C1 and C2 are connected in series?
a) (C1+C2)/C1C2
b) 1/C1+1/C2
c) C1C2/(C1+C2)
d) C1+C2

View Answer

Answer: c [Reason:] When capacitors are connected in series, the equivalent capacitance is: 1/Ctotal=1/C1+1/C2, therefore Ctotal= C1C2/(C1+C2).

2. N capacitors having capacitance C are connected in series, calculate the equivalent capacitance.
a) C/N
b) C
c) CN
d) N/C

View Answer

Answer: d [Reason:] When capacitors are connected in series, the equivalent capacitance is: 1/Ctotal= 1/C+1/C+1/C+……..N times. 1/Ctotal=N/C. Ctotal=C/N.

3. When capacitors are connected in series, the equivalent capacitance is ___________ each individual capacitance.
a) Greater than
b) Less then
c) Equal to
d) Insufficient data provided

View Answer

Answer: b [Reason:] When capacitors are connected in series, the equivalent capacitance is: 1/Ctotal=1/C1+1/C2. Since we find the reciprocals of the sum of the reciprocals, the equivalent capacitance is less than the individual capacitance values.

4. What is the equivalent capacitance?
basic-electrical-engineering-questions-answers-capacitors-series-q4
a) 1.5F
b) 0.667F
c) 2.45F
d) 2.75F

View Answer

Answer: b [Reason:] When capacitors are connected in series, the equivalent capacitance is: 1/Ctotal=1/C1+1/C2= 1/2+1= 0.667F.

5. When capacitors are connected in series ___________ remains the same.
a) Voltage across each capacitor
b) Charge
c) Capacitance
d) Resistance

View Answer

Answer: b [Reason:] When capacitors are connected in series, the charge remains the same because the same amount of current flow exists in each capacitor.

6. When capacitors are connected in series _______________ Varies
a) Voltage across each capacitor
b) Charge
c) Capacitance
d) Resistance

View Answer

Answer: a [Reason:] When capacitors are connected in series, the voltage varies because the voltage drop across each capacitor is different.

7. Four 10F capacitors are connected in series, calculate the equivalent capacitance.
a) 0.2F
b) 0.4F
c) 0.5F
d) 0.6F

View Answer

Answer: b [Reason:] When capacitors are connected in series, the equivalent capacitance is: 1/Ctotal=1/C1+1/C2+1/C3+1/C4=1/10+1/10+1/10+1/10=0.4F.

8. Calculate the charge in the circuit.
basic-electrical-engineering-questions-answers-capacitors-series-q8
a) 66.67C
b) 20.34C
c) 25.45C
d) 30/45C

View Answer

Answer: a [Reason:] When capacitors are connected in series, the equivalent capacitance is: 1/Ctotal=1/C1+1/C2= 1/2+1=0.667F. Q=CV= 1.5*100= 66.67C.

9. Calculate the voltage across the 1F capacitor.
basic-electrical-engineering-questions-answers-capacitors-series-q8
a) 33.33V
b) 66.67V
c) 56.56V
d) 23.43V

View Answer

Answer: b [Reason:] When capacitors are connected in series, the equivalent capacitance is: 1/Ctotal=1/C1+1/C2= 1/2+1=0.667F. Q=CV= 1.5*100= 66.67C. V across the 1F capacitor= 66.67/1= 66.67V.

10. Calculate the voltage across the 2F capacitor.
basic-electrical-engineering-questions-answers-capacitors-series-q8
a) 33.33V
b) 66.67V
c) 56.56V
d) 23.43V

View Answer

Answer: a [Reason:] When capacitors are connected in series, the equivalent capacitance is: 1/Ctotal=1/C1+1/C2= 1/2+1=0.667F. Q=CV= 1.5*100= 66.67C. V across the 1F capacitor= 66.67/2= 33.33V.