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MCQs on Electric Circuits

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01․ If 1 A current flows in a circuit, the number of electrons flowing through this circuit is
0.625 × 1019
1.6 × 1019
1.6 × 10 - 19
0.625 × 10 - 19

The charge of one electron is 1.6 × 10 - 19 coulomb. Again 1 A current means transferring of 1 coulomb charge per one second.
02․ The resistivity of the conductor depends on
area of the conductor.
length of the conductor.
type of material.
none of these.

The resistivity is a property of a material, defined as the resistance between two opposite faces of a cube of a material of unit volume. That is why resistivity is only the unique property of a material and it does not depend upon the dimension of any piece of material. The same can also be explained as Where, ρ is the resistivity; m and e is the mass and charge of an electron; T is the relaxation time. All these are properties of a material and independent of length and cross sectional area.
03․ The resistance of a conductor of diameter d and length l is R Ω. If the diameter of the conductor is halved and its length is doubled, the resistance will be
R Ω
2R Ω
4R Ω
8R Ω

As per law of resistance, the resistance of the conductor is inversely proportional to its cross-sectional area i.e. it is inversely proportional to the square of the diameter of cross-sectional area of the conductor. As per same law of resistance, the resistance of the conductor is directly proportional to the length of the conductor.
04․ How many coulombs of charge flow through a circuit carrying a current of 10 A in 1 minute?
10
60
600
1200

1 Ampere current means flowing of 1 Coulomb charge per second. That means 10 A current in 1 minute or 60 seconds implies 10 × 60 = 600 coulombs.
05․ A capacitor carries a charge of 0.1 C at 5 V. Its capacitance is
0.02 F
0.5 F
0.05 F
0.2 F

The capacitance of a capacitor is expressed by Q/V. Where Q is the charge of the capacitor and V is the voltage across the capacitor.
06․ To obtain a high value of capacitance, the permittivity of dielectric medium should be
low
zero
high
unity

The expression of capacitance is given as Where ε is the permittivity of the medium. Hence it is seen that the capacitance of a capacitor is directly proportional to the permittivity of the medium used as dielectric. Therefore to obtain a high value of capacitance, the permittivity of dielectric medium should be high.
07․ Four capacitors each of 40 µF are connected in parallel, the equivalent capacitance of the system will be
160 µF
10 µF
40 µF
5 µF

The impedance of a capacitor is inversely proportional to its capacitance value. Reciprocal of equivalent impedance of parallel connected circuit elements is sum of reciprocal of impedance of each of the elements.
08․ Five capacitors each of 5 µF are connected in series, the equivalent capacitance of the system will be
5 µF
25 µF
10 µF
1 µF

When numbers of circuit elements are connected in series, the impedance of equivalent combination is sum of impedance of all elements in series. Again, capacitance is inversely proportional to impedance. Hence, when capacitors are connected in series
09․ 1 F is theoretically equal to
1 ohm of resistance
ratio of 1 V to 1 C
ratio of 1 C to 1 V
none of these

1 Farad capacitance is defined as the capacity of dielectric medium to store 1 Coulomb charge when 1 Volt potential difference is applied across it. Thus, capacitance is expressed as the ratio of charge to voltage (Q = CV).
10․ The unit of resistivity is
Ω.
Ω - metre.
Ω / metre.
Ω / m².

11․ Instantaneous power in inductor is proportional to the
product of the instantaneous current and rate of change of current.
square of instantaneous current.
square of the rate of change of current.
temperature of the inductor.

The instantaneous voltage across the inductor is expressed as the product of inductance and rate of change of current through it. Power is expressed as the product of current and voltage. Hence instantaneous power in an inductor is proportional to the product of instantaneous current and rate of change of current through it.
12․ The voltage induced in an inductor is represented as,
product of its inductance and current through it.
ratio of its inductance to current through it.
ratio of current through it to its inductance.
product of its inductance and rate of change of current through it.

The instantaneous voltage across the inductor is expressed as the product of inductance and a rate of change of current through it as it doesn't allow any certain change of current through it. Voltage induced in an inductor is written as
13․ Absolute permittivity of dielectric medium is represented as
ε0
εr
εr0
εrε0

The relative permittivity (εr) of the medium is defined as the ratio of actual permittivity of the medium to the absolute permittivity of air or vacuum. Absolute permittivity of air or vacuum is expressed as ε0. Hence the absolute permittivity of dielectric medium is represented as the product of relative permittivity of the medium and absolute permittivity of air or vacuum.
14․ Magnetic flux has the unit of
Newton
Ampere turn
Weber
Tesla

The unit of magnetic flux is called Weber in honor of famous scientist Wilhelm Eduard Weber (1804 – 1891). Magnetic flux has also another unit named Maxwell. 1 Maxwell = 10-8 Weber.
15․ If all the elements in a particular network are linear, then the superposition theorem would hold, when the excitation is
DC only
AC only
Either AC or DC
An Impulse

Superposition theorem can be applied for both AC as well DC excitation to calculate the voltage or current calculations. It holds for both DC and AC excitation, if the circuit is linear. But superposition theorem is not applicable for power calculations.
16․ In balanced bridge, if the positions of detector and source are interchanged, the bridge will still remain balanced. This can be explained from which theoem
Reciprocity theorem
Thevinin's theorem
Norton's theorem
Compensation theorem

When response to excitation is constant even though we interchange the excitation and responses then the reciprocity theorem is verified for the given network.
17․ If P is the power of a star connected system then what will be power of an equivalent delta connected system?
P
3P
P/3
None of the above

The power in both of the connections is same either it is connected in Star or Delta.
18․ Which of the followings is/are active element?
Voltage source
Current source
Both
None of these.

Active elements are capable of delivering energy independently for long time or ideally infinite time. Both voltage and current source are active element and they can change energy level of a circuit.
19․ Which of the following are the passive elements?
Resistor
Bulb
Both
None of these.

When the element is not capable of delivering energy independently, are called as passive element. Both resistor and bulb are the passive elements and they can't increase the energy level of a circuit.
20․ Power dissipation in ideal inductor is
Maximum
Minimum
Zero
A finite value

Internal resistance of ideal inductor is zero. As there is no resistance, there should not be any dissipation of power. Pure inductor has no resistive component, so it active power dissipation is zero.
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