MCQs on Electric Circuits
01․ If 1 A current flows in a circuit, the number of electrons flowing through this circuit is
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
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
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?
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
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
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
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
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 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
11․ Instantaneous power in inductor is proportional to the
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,
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
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
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
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
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?
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?
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?
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
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.123>>>