Test: Current & Voltage in an Inductive Circuit, Capacitive Circuit


20 Questions MCQ Test Basic Electrical Technology | Test: Current & Voltage in an Inductive Circuit, Capacitive Circuit


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QUESTION: 1

Inductor does not allow sudden changes in?

Solution:

The inductor does not allow sudden changes in current because if current changes in the inductor occur in zero time, the voltage becomes zero which is not possible.

QUESTION: 2

 In case of Inductive circuit, Frequency is ______________ to the current.

Solution:

Inductance is inversely proportional to current since, as the inductance increases, current decreases.

QUESTION: 3

 If the resistance in a circuit is 2 ohm and the inductive resistance is 20 ohm, calculate the power factor.

Solution:

We know that:
cos(phi)=R/XL
From the given question, we find that the power factor is 10.

QUESTION: 4

 If the power factor is 10 and the resistance is 2 ohm, calculate the inductive reactance.

Solution:

 We know that:
cos(phi)=R/XL
From the given question, we find that the inductive reactance is 20 ohm.

QUESTION: 5

An induced emf is said to be ___________

Solution:

Any circuit in which a change of current is accompanied by a change of flux, and therefore by an induced emf, is said to be inductive.

QUESTION: 6

In a pure inductive circuit, the power factor is?

Solution:

In a pure inductive circuit, current is lagging by 90 degrees from the voltage. The power factor is the cosine of the angle in between the voltage and the current. If the angle between the voltage and current is 90, then cos90=0. Hence, the power factor is zero.

QUESTION: 7

Among the following, which is the right formula for inductance?

Solution:

The average emf induced is proportional to the current per unit time, the constant of proportionality being L. Hence emf=LI/t. Making L the subject of the formula, we get: L=emf*t/I.

QUESTION: 8

Among the following, which is the right formula for inductance?

Solution:

The average emf induced in a coil is L=NΦ/t.

QUESTION: 9

If the current in a coil having a constant inductance of L henrys grows at a uniform rate, what is the value of the average current?

Solution:

The average current is the average of the current which flows in the inductor. Hence it is I/2.

QUESTION: 10

Find the average current in an inductor if the total current in the inductor is 30A.

Solution:

Average current= I/2.
Substituting the value of I from the equation, average current= 13A.

QUESTION: 11

What happens to the voltage in a capacitive circuit when the frequency increases?

Solution:

The capacitive reactance decreases as the frequency increases since they are in-versely proportional. The voltage is directly proportional to the capacitive reactance, hence it de-creases.

QUESTION: 12

When voltage across a capacitor increases, what happens to the charge stored in it?

Solution:

When voltage across a capacitor increases, the charge stored in it also increases be-cause charge is directly proportional to voltage, capacitance being the constant of proportionality.

QUESTION: 13

What happens to the current flow in a fully charged capacitor?

Solution:

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.

QUESTION: 14

What is the correct formula for capacitive reactance?

Solution:

The capacitive reactance Xc is the reciprocal of the product of the angular velocity and the capacitance. The angular velocity=2*pi*f, therefore Xc=1/(2*f*pi*C).

QUESTION: 15

Calculate the capacitance of a capacitor that stores 80microC of charge and has a voltage of 4V.

Solution:

Q is directly proportional to V. The constant of proportionality in this case is C, that is, the capacitance. Hence C=Q/V.
C=80microC/4V=20microF.

QUESTION: 16

What happens to the current in a capacitive circuit when the frequency increases?

Solution:

 The capacitive reactance decreases as the frequency increases since they are in-versely proportional. The current is inversely proportional to the capacitive reactance, hence it in-creases.

QUESTION: 17

Calculate the current in the capacitor having 2V supply voltage and 3F capacitance in 2seconds.

Solution:

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.

QUESTION: 18

 If 2V is supplied to a 3F capacitor, calculate the charge stored in the capacitor.

Solution:

 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.

QUESTION: 19

A 30 microF capacitor is connected across a 400V, 50Hz supply. Calculate the capacitive reac-tance.

Solution:

We know that: Xc=1/(2*f*pi*C).
Substituting the values from the given question, we get Xc= 106.2 ohm.

QUESTION: 20

 A 30 microF capacitor is connected across a 400V, 50Hz supply. Calculate the current.

Solution:

We know that: Xc=1/(2*f*pi*C).
Substituting the values from the given question, we get Xc= 106.2 ohm.
I=V/Xc, hence I= 3.77A.