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# Multiple choice question for engineering

## Set 1

1. Magnetic field lines seek the path of __________ resistance.
a) Maximum
b) Minimum
c) Infinite
d) Zero

Answer: b [Reason:] Magnetic field lines will always seek the path of least resistance. It does not seek the path of zero resistance because, in practical scenarios, zero resistance is not possible.

2. Magnetic field lines form _________ loops from pole to pole.
a) Open
b) Closed
c) Branched
d) Either closed or branched

Answer: b [Reason:] Magnetic field lines form closed loops from pole to pole. There is no discontinuity in the magnetic flux lines.

3. Do magnetic flux lines intersect?
a) Yes
b) No
c) Depends on the situation
d) Cannot be determined

Answer: b [Reason:] Magnetic field lines do not cross each other because if they cross it means the there are two different directions of magnetic field in that region and that is not possible.

4. Magnetic field lines ___________ at the south pole.
a) Emerge
b) Converge
c) Neither emerge nor converge
d) Either emerge or converge

Answer: b [Reason:] Magnetic field lines converge at the south pole. Field lines seem to converge at the south pole because they end at the south pole.

5. Magnetic field lines ___________ at the north pole.
a) Emerge
b) Converge
c) Neither emerge nor converge
d) Either emerge or converge

Answer: a [Reason:] Magnetic field lines emerge at the north pole. Field lines seem to emerge at the north pole because they originate at the north pole.

6. Field lines move from __________
a) North to south
b) South to north
c) West to east
d) East to west

Answer: a [Reason:] Magnetic field lines originate at the north pole and terminate at the south pole of the magnet.

7. Inside the magnet, field lines travel from?
a) North to south
b) South to north
c) West to east
d) East to west

Answer: b [Reason:] Magnetic field lines originate at the north pole and terminate at the south pole of the magnet but inside the magnet, they seem to move from south to north.

8. Can we see magnetic flux lines?
a) Yes
b) No
c) Depends on the strength of the field
d) Only when field strength is very large

Answer: b [Reason:] No, we cannot see magnetic flux lines as the “lines of magnetic flux” is purely an imaginary concept to understand the magnetic field clearly.

9. Lines of magnetic flux which are parallel and in the same direction __________ each other.
a) Attract
b) Repel
c) Intersect
d) Cancel

Answer: b [Reason:] Lines of magnetic flux which are parallel to each other and in the same direction repel each other because they tend to act as like poles and like poles repel each other.

10. More the number of magnetic flux lines, _______ is the force of the magnet.
a) Greater
b) Lesser
c) Either greater or lesser
d) Neither greater nor lesser

Answer: a [Reason:] More the number of magnetic flux lines, greater is the force of the magnet. This is because the magnetic flux lines denote the strength of the field of the magnet.

## Set 2

1. Which among the following expressions relate charge, voltage and capacitance of a capacitor?
a) Q=C/V
b) Q=V/C
c) Q=CV
d) C=Q2V

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

2. If a 2F capacitor has 1C charge, calculate the voltage across its terminals.
a) 0.5V
b) 2V
c) 1.5V
d) 1V

Answer: b [Reason:] Q is directly proportional to V. The constant of proportionality in this case is C, that is, the capacitance. Hence C/Q=V. V=2/1=1V.

3. What is the voltage across a capacitor at the time of switching, that is, when t=0?
a) Infinity
b) 0V
c) Cannot be determined
d) 1V

Answer: b [Reason:] At the time of switching, when t=0, the capacitor acts as a short circuit. The voltage across a short is always equal to zero hence the voltage across the capacitor is equal to zero.

4. What is the voltage across the capacitor if the switch is closed and steady state is reached? a) 8V
b) 0V
c) 10V
d) Infinity

Answer: c [Reason:] When steady state is reached, the capacitor acts as a short circuit and the 10V is connected in parallel to it. Hence Vc=10V.

5. If one plate of a parallel plate capacitor is charged to positive charge the other plate is charged to?
a) Positive
b) Negative
c) Positive of negative
d) Not charged

Answer: b [Reason:] If one plate is charged to positive, the other plate is automatically charges to negative so that it can store electrical charge.

6. When voltage across a capacitor increases, what happens to the charge stored in it?
a) Increases
b) Decreases
c) Becomes zero
d) Cannot be determined

Answer: a [Reason:] When voltage across a capacitor increases, the charge stored in it also increases because charge is directly proportional to voltage, capacitance being the constant of proportionality.

7. When will capacitor fully charged?
a) When the voltage across its plates is half the voltage from ground to one of its plates
b) When current through the capacitor is a 1/root2 time its value
c) When the supply voltage is equal to the capacitor voltage
d) Never

Answer: c [Reason:] When the capacitor voltage is equal to the supply voltage the current stops flowing through the circuit and the charging phase is over.

8. What happens to the current flow in a fully charged capacitor?
a) Current flow stops
b) Current flow doubles
c) Current flow becomes half its original value
d) Current flow becomes one-fourth its original value

Answer: a [Reason:] When a capacitor is fully charged, it does not store any more charge. There is no change in charge with time. Current is the rate of change of charge, hence it becomes zero, or stops.

9. Calculate the capacitance of a capacitor that stores 40microC of charge and has a voltage of 2V.
a) 20F
b) 20microF
c) 10F
d) 10microF

Answer: b [Reason:] Q is directly proportional to V. The constant of proportionality in this case is C, that is, the capacitance. Hence C=Q/V. C=40microC/2V=20microF.

10. What happens to the capacitance when the voltage across the capacitor increases?
a) Decreases
b) Increases
c) Becomes 0
d) No affect

Answer: a [Reason:] The capacitance is inversely proportional to the voltage across its terminals(C=Q/V). Hence as voltage increases, capacitance decreases.

## Set 3

1. Which of the following charging and discharging of a capacitor?
a) Time constant
b) Current
c) Power
d) Voltage

Answer: a [Reason:] The time constant in a circuit consisting of a capacitor is the product of the resistance and the capacitance. Smaller the time constant, faster is the charging and discharging rate and vice versa.

2. What is the initial current while charging a capacitor?
a) High
b) Low
c) 0
d) Cannot be determined

Answer: a [Reason:] The initial current of a capacitor is very high because the voltage source will transport charges from one plate of the capacitor to the other plate.

3. What is the final current while charging a capacitor?
a) High
b) Zero
c) Infinity
d) Low

Answer: b [Reason:] The final current is almost equal to zero while charging a capacitor because the capacitor is charged up to the source voltage.

4. What happens to the current flow in a fully charged capacitor?
a) Current flow stops
b) Current flow doubles
c) Current flow becomes half its original value
d) Current flow becomes one-fourth its original value

Answer: a [Reason:] When a capacitor is fully charged, it does not store any more charge. There is no change in charge with time. Current is the rate of change of charge, hence it becomes zero, or stops.

5. A capacitor is charged to a voltage of 400V and has a resistance of 20ohm. Calculate the initial value of discharge current.
a) 10A
b) 0A
c) Infinity
d) 20A

Answer: d [Reason:] When the capacitor is discharging the value of initial current is a finite one. The finite initial current value is found using ohm’s law: I=V/R= 400/20= 20A.

6. A capacitor is charged to a voltage of 400V and has a resistance of 20ohm. Calculate the final value of discharge current.
a) 10A
b) 0A
c) Infinity
d) 20A

Answer: b [Reason:] In a discharging circuit, the final voltage is equal to zero as all the positive and negative charges have combined. Since the voltage is equal to zero, the current is also equal to zero as voltage is directly proportional to current by ohm’s law.

7. When will be capacitors fully charged?
a) When voltage is zero
b) When the supply voltage is equal to the capacitor voltage
c) When voltage is infinity
d) When capacitor voltage is equal to half the supply voltage

Answer: b [Reason:] When the capacitor voltage is equal to the source voltage, it means that all the charges have moved from one plate of the capacitor to the other.

8. What happens to the capacitor when the capacitor voltage is equal to the source voltage?
a) The charging phase of the capacitor is over
b) The discharging phase of the capacitor is over
c) The capacitor is switched off
d) The capacitor is switched on

Answer: a [Reason:] When the capacitor voltage is equal to the source voltage, it means that all the charges have moved from one plate of the capacitor to the other. Hence the capacitor is charged and the charging phase is over.

9. A capacitor is charged to a voltage of 400V and has a resistance of 20ohm. Calculate the final value of charging current.
a) 10A
b) 0A
c) Infinity
d) 20A

Answer: d [Reason:] The final value of charging current in a capacitor is equal to the initial value of discharging current in it. Hence the final value of charging current is: Vc/R=20A.

10. A capacitor is charged to a voltage of 400V and has a resistance of 20ohm. Calculate the initial value of charging current.
a) 10A
b) 0A
c) Infinity
d) 20A

Answer: b [Reason:] Initially, there’s 0V voltage in a capacitor. As the capacitor charges, the voltage increases. Since voltage is proportional to current by ohm’s law, initial current is also equal to zero.

## Set 4

1. What is the equivalent inductance when inductors are connected in series?
a) Sum of all the individual inductances
b) Product of all the individual inductances
c) Sum of the reciprocal of all the individual inductances
d) Product of the reciprocal of all the individual inductances

Answer: a [Reason:] When inductances are connected in series, the equivalent inductance is equal to the sum of all the individual inductance values.

2. When inductances are connected in series, the equivalent inductance is ____________ the largest individual inductance.
a) Greater than
b) Less than
c) Equal to
d) Not related to

Answer: a [Reason:] When inductances are connected in series, the equivalent inductance is equal to the sum of all the individual inductance values. Hence the equivalent inductance is greater than the largest individual inductance.

3. Three inductors having inductance values 3H, 4H and 5H are connected in series, calculate the equivalent inductance.
a) 10H
b) 12H
c) 3H
d) 5H

Answer: b [Reason:] When inductances are connected in series, the equivalent inductance is equal to the sum of all the individual inductance values. Hence Leq= L1+L2+L3= 12H.

4. Calculate the equivalent inductance between A and B. a) 30H
b) 54H
c) 44H
d) 60H

Answer: c [Reason:] The 4 inductors are connected in series, hence their equivalent inductance is: Leq=L1+L2+L3+L4=44H.

5. When inductors are connected in series, the voltage across each inductor is _________
a) Equal
b) Different
c) Zero
d) Infinity

Answer: b [Reason:] In a series circuit, the current across all elements remain the same and the total voltage of the circuit is the sum of the voltages across all the elements.

6. If there are two bulbs connected in series and one blows out, what happens to the other bulb?
a) The other bulb continues to glow with the same brightness
b) The other bulb stops glowing
c) The other bulb glows with increased brightness
d) The other bulb also burns out

Answer: b [Reason:] Since the two bulbs are connected in series, if the first bulb burns out there is a break in the circuit and hence the second bulb does not glow.

7. Voltage across a series resistor circuit is proportional to?
a) The amount of time the circuit was on for
b) The value of the inductance itself
c) The value of the other inductances in the circuit
d) The power in the circuit

Answer: b [Reason:] V=IXL hence voltage is proportional to the value of the inductive impedance which is proportional to the inductance. Thus voltage is proportional to the inductance.

8. What is the voltage measured across a series short?
a) Infinite
b) Zero
c) The value of the source voltage
d) One

Answer: b [Reason:] A short is just a wire. The potential difference between two points of a wire is zero hence the voltage measured is equal to zero.

9. In a series circuit, which of the parameters remain constant across all circuit elements such as resistor, capacitor, inductor etcetera?
a) Voltage
b) Current
c) Both voltage and current
d) Neither voltage nor current

Answer: b [Reason:] In a series circuit, the current across all elements remain the same and the total voltage of the circuit is the sum of the voltages across all the elements.

10. Batteries are generally connected in?
a) Series
b) Parallel
c) Either series or parallel
d) Neither series nor parallel

Answer: a [Reason:] Batteries are generally connected in series so that we can obtain the desired voltage since voltages add up once they are connected in series.

## Set 5

1. Potential drop in a dielectric is equal to _______
a) Electric field strength*thickness
b) Electric field strength*area of cross section
c) Electric field strength
d) Zero

Answer: a [Reason:] When a dielectric is introduced between the two plates of a parallel plate capacitor, the potential difference decreases by the value of the product of electric field strength*thickness which is the potential difference of the dielectric.

2. The electric field strength is 10N/C and the thickness of the dielectric is 3m. Calculate the potential drop in the dielectric.
a) 10V
b) 20V
c) 30V
d) 40V

Answer: c [Reason:] The potential drop in a dielectric= electric field strength*area of cross section= 10*3= 30V.

3. The electric fields of dielectrics having the same cross sectional area in series is related to their relative permittivities in which way?
a) Directly proportional
b) Inversely proportional
c) Equal
d) Not related

Answer: b [Reason:] Let us consider two plates having fields E1 and E2 and relative permittivities e1 and e2. Then, E1=Q/(e0*e1*A) and E2=Q/(e0*e2*A), where e0=absolute permittivity and A=area of cross section. From the given expression, we see that E1/E2=e2/e1, hence the electric field is inversely proportional to the relative permittivities.

4. What happens to the capacitance when a dielectric is introduced between its plates?
a) Increases
b) Decreases
c) Remains the same
d) Becomes zero

Answer: a [Reason:] The capacitance of a capacitance increases when a dielectric is introduced between its plates because the capacitance is related to the dielectric constant k by the equation: C=ke0A/d.

5. Calculate the relative permittivity of the second dielectric if the relative permittivity of the first is 4. The electric field strength of the first dielectric is 8V/m and that of the second is 2V/m.
a) 32
b) 4
c) 16
d) 8

Answer: c [Reason:] The relation between the two electric fields and the relative permittivities is: E1/E1=e2/e1. Substituting the given values, we get e2=16.

6. What happens to the potential drop between the two plates of a capacitor when a dielectric is introduced between the plates?
a) Increases
b) Decreases
c) Remains the same
d) Becomes zero

Answer: b [Reason:] When a dielectric is introduced between the two plates of a parallel plate capacitor, the potential difference decreases because the potential difference of the dielectric is subtracted from it.

7. If the potential difference across the plates of a capacitor is 10V and a dielectric having thickness 2m is introduced between the plates, calculate the potential difference after introducing the dielectric. The electric field strength is 2V/m.
a) 4V
b) 6V
c) 8V
d) 10V

Answer: b [Reason:] When a dielectric is introduced between the plates of a capacitor, its potential difference decreases. New potential difference= potential difference without dielectric-potential difference of dielectric= 10-2*2= 6V.

8. Calculate the capacitance if the dielectric constant=4, area of cross section= 10m2 and the distance of separation between the plates is 5m.
a) 7.08*10-11F
b) 7.08*1011F
c) 7.08*10-12F
d) 7.08*10-10F

Answer: a [Reason:] The expression to find capacitance when a dielectric is introduced between the plates is: C=ke0A/d. Substituting the given values in the equation, we get C= 7.08*10-11F.

9. A dielectric is basically a ________
a) Capacitor
b) Conductor
c) Insulator
d) Semiconductor

Answer: c [Reason:] A dielectric is basically an insulator because it has all the properties of an insulator.

10. What happens to the potential difference between the plates of a capacitor as the thickness of the dielectric slab increases?
a) Increases
b) Decreases
c) Remains the same
d) Becomes zero