# Measurement of RLC Using Bridge Circuits MCQ || Measurement of RLC Questions and Answers

1. For measurement of mutual inductance, we can use

1. Anderson bridge
2. Maxwell’s bridge
3. Heaviside bridge
4. None of these

Explanation:

Heaviside Bridge measures mutual inductance in terms of a known self-inductance. The same bridge, slightly modified, was used by Campbell to measure a self-inductance in terms of a known mutual inductance.

 Type of Bridge Name of Bridge Used to measure Important DC Bridges Wheatstone bridge Medium resistance Corey foster’s bridge Medium resistance Kelvin double bridge Very low resistance Loss of charge method High resistance Megger High insulation resistance Resistance of cables AC Bridges Maxwell’s inductance bridge Inductance Not suitable to measure Q Maxwell’s inductance capacitance bridge Inductance Suitable for medium Q coil (1 < Q < 10) Hay’s bridge Inductance Suitable for high Q coil (Q > 10), slowest bridge Anderson’s bridge Inductance 5-point bridge, accurate and fastest bridge (Q < 1) Owen’s bridge Inductance Used for measuring low Q coils Heaviside mutual inductance bridge Mutual inductance Campbell’s modification of Heaviside bridge Mutual inductance De-Sauty’s bridge Capacitance Suitable for perfect capacitor Schering bridge Capacitance Used to measure relative permittivity, dielectric loss Wein’s bridge Capacitance and frequency Harmonic distortion analyzer, used as a notch filter, used in audio and high-frequency applications

2. The test used to locate high resistance faults in low resistance conductor circuit is:

1. Hopkinson’s test
2. Murray loop test
3. Star/delta loop test
4. Open circuit test

Explanation:

Murray loop test is the most common and accurate method for locating earth faults and short-circuit faults.

Murray loop test is the most common method for locating high resistance faults in low resistance conductor circuits. It employs the principle of the Wheatstone bridge to determine the fault location.

3. Insulation resistance of a cable can be measured by

1. Megger
2. Galvanometer Method
3. Both 1 and 2
4. Murray method

Explanation:

In Galvanometer Method the high resistance under measurement is determined by the deflection of the galvanometer, hence the method called Direct Deflection Method. This method is similar to the principle of the ammeter-voltmeter method used for measuring low and medium resistance.

Many sensitive types of galvanometers can detect currents from 0.1 – 1 nA. Therefore, with an applied voltage of 1 kV, resistances are as high as 1012 to 10 × 1012 can be measured.

In the Loss of charge method, the insulation resistance R to be measured is connected in parallel with a capacitor C and an electrostatic voltmeter.

The capacitor is charged to some suitable voltage, by means of a battery having voltage V and is then allowed to discharge through the resistance. The terminal voltage is observed over a considerable period of time during discharge.

• Megger is a measuring instrument used for the measurement of the insulation resistance of an electrical system
• An electrical system degrades its quality of insulation resistance with time and various environmental conditions including temperature, moisture, dust particles & humidity
• Even mechanical and electrical stress affects the insulation resistance which adds to the necessity of checking insulation resistance at regular intervals so as to avoid fatal errors or electrical shocks
• Megger is used for measuring the electrical leakage in wires, electrical insulation levels in generators, motors, etc

4. A megger is a device used for measuring:

1. Extremely high resistances
2. Extremely high voltages
3. Extremely high currents
4. All of the above

Explanation:

The Megger insulation tester is a small, portable instrument that gives you a direct reading of insulation resistance in ohms or megohms. For good insulation, the resistance usually reads in the megohm range.

The Megger method is used for the measurement of the high value of resistance. And this is best suitable for the measurement of insulation resistance of cables.

5. The electrical power to a megger is provided by

1. Battery
2. Permanent magnet D.C. generator
3. AC generator
4. Either AC or DC generator

Explanation:

• Megger is a portable instrument to measure high insulation resistances
• It basically works on the principle of electromagnetic induction
• The electrical power to a megger is provided by a permanent magnet D.C. generator
• The test voltages are usually of order 500, 1000, or 2500 V are generated by a hand-driven generator (permanent magnet D.C. generator)

6. A megger is an instrument that gives the reading in:

1. volt
2. ohm
3. henry
4. ampere

Explanation:

The Megger insulation tester is a small, portable instrument that gives you a direct reading of insulation resistance in ohms or megohms. For good insulation, the resistance usually reads in the megohm range.

7. In case of the Wheatstone bridge shown in the below circuit diagram P = 3 kΩ and Q = 5 kΩ. The null value for the galvanometer is obtained when S = 6 kΩ. Find the value of R and the resistance measurement range of the bridge if ‘S’ value varies from 1 kΩ to 8 kΩ 1. R = 2.6 kΩ , S = 500 Ω to 3.8 kΩ
2. R = 5.6 kΩ, S = 400 Ω to 5.8 kΩ
3. R = 3.6 kΩ, S = 500 Ω to 5.8 kΩ
4. R = 3.6 kΩ, S = 600 Ω to 4.8 kΩ

Answer:4. R = 3.6 kΩ, S = 600 Ω to 4.8 kΩ

Explanation:

We know that the balanced condition of a bridge

P × S = R × Q

R = (P × S)/Q

= (3 × 6)/5 = 3.6 kΩ

Now take minimum value of S = 1 kΩ

R = (P × S)/Q

= (3 × 1)/5 = 600 Ω

Now take the maximum value of S = 8 kΩ

R = (P × S)/Q

= (3 × 8)/5 = 4.8 Ω

∴ Range of bridge = 600 Ω to 4.8 kΩ

8. Ballistic galvanometer with high oscillation period and high critical resistance would be best suited for measurement of _____.

1. Capacitance
2. Inductance
3. Current
4. Voltage

Explanation:

The principle behind the ballistic galvanometer working is that it measures the amount of charge that flows across the magnetic coil where which initiates the coil to move.

The following are the methods used for determining the constant of the ballistic galvanometer.

Using a Capacitor: The charging and discharging of the capacitor gives the values of the ballistic galvanometer constant. The circuit arrangement for the calibration of a ballistic galvanometer using the capacitor is shown in the figure below. If we charge up a capacitor (C) to a known potential V and then discharge it through a ballistic galvanometer the charge passed through the galvanometer is proportional to the first deflection of the instrument (θ1). and so if the value of one of the capacitors is known the capacitance of the other may be found.

9. Direct Deflection method is also called as ______

1. Capacitance Method
2. Galvanometer Method
3. Resistance Method
4. Murray method

Explanation:

Direct Deflection method is also called as Galvanometer Method.

In Galvanometer Method the high resistance under measurement is determined by the deflection of the galvanometer, hence the method called Direct Deflection Method. This method is similar to the principle of the ammeter-voltmeter method used for measuring low and medium resistance.

10. Which bridge is used to determine frequency?

1. Anderson bridge
2. Desauty bridge
3. Wien bridge
4. Campbell bridge

Explanation:

The Wien’s bridge is an AC electrical circuit widely used for measuring frequency and can also be used for the measurement of capacitance with high accuracy. The bridge can be used even at high voltages but the circuit is sensitive to frequency.

11. Which of the following bridge is most suitable for the measurement of an unknown capacitance?

1. Wheatstone Bridge
2. Owen’s Bridge
3. Anderson Bridge
4. Schering Bridge

Explanation:

The Schering bridge is used for measuring the capacitance of the capacitor, dissipation factor, properties of an insulator, capacitor bushing, insulating oil and other insulating materials. It is one of the most commonly used AC bridges. The Schering bridge works on the principle of balancing the load on its arm.

12. In wire-wound strain gauges, the change in resistance under strained conditions is mainly on account of _____

1. Change in diameter of the wire
2. Change in length of the wire
3. Change in both length and diameter of wire
4. Change in resistivity

Answer:3. Change in both length and diameter of wire

Explanation:

Let us consider a strain gauge made of circular wire.

The wire has the dimensions before being strained.

Length = L, area = A, diameter = D

The material of the wire has a resistivity ρ

Resistance of unstrained gauge R = ρL/A

Let a tensile stress s be applied to the wire. This produces a positive strain causing the length to increase and area to decrease.

Thus, when the wire is strained there are changes in its dimensions.

Let ΔL = change in length

ΔA = change in area

ΔD = change in diameter

In order to find how ΔR depends upon the material physical quantities, the expression for R is differentiated with respect to stress s.

$$\frac{{dR}}{{ds}} = \frac{\rho }{A}\frac{{\partial L}}{{\partial s}} – \;\frac{{\rho L}}{{{A^2}}}\frac{{\partial A}}{{\partial s}} + \frac{L}{A}\frac{{\partial \rho }}{{\partial s}}$$

By dividing throughout by resistance R = ρL/A

$$\Rightarrow \frac{1}{R}\frac{{dR}}{{ds}} = \frac{1}{L}\frac{{\partial L}}{{\partial s}} – \;\frac{1}{A}\frac{{\partial A}}{{\partial s}} + \frac{1}{\rho }\frac{{\partial \rho }}{{\partial s}}$$

From the above equation, as the resistivity is almost constant, it is evident that the per unit change in resistance is mainly due to

• Per unit change in length
• Per unit change in area or diameter

13. Determine the quality factor for Maxwell’s inductance capacitance bridge given below when the bridge is supplied by a frequency of 50 Hz. 1. 0.16
2. 0.27
3. 0.36
4. 0.47

Explanation:

At balance condition

$$\begin{array}{l} {Z_1}{Z_4} = {Z_2}{Z_3}\\ \left( {{R_x} + j\omega {L_x}} \right)\left( {\frac{{60.\frac{1}{{j\omega C}}}}{{60 + \frac{1}{{j\omega C}}}}} \right) = 35 \times 15 \end{array}$$

$$\begin{array}{l} \left( {{R_x} + j\omega {L_x}} \right)\left( {\frac{1}{{1 + j60\omega C}}} \right) = \frac{{35}}{4}\\ \left( {{R_x} + j\omega {L_x}} \right)\left( {1 – j60\omega C} \right) = \frac{{35}}{4}\left( {1 + {{60}^2}{\omega ^2}{C^2}} \right) \end{array}$$

$${R_x} + 60{\omega ^2}C{L_x} + j\left( {\omega {L_x} – 60{R_x}\omega C} \right) = \frac{{35}}{4}\left( {1 + {{60}^2}{\omega ^2}{C^2}} \right)$$

Compare real parts of the above equation,

$$\begin{array}{l} {R_x} + 60{\omega ^2}C{L_x} = \frac{{35}}{4}\left( {1 + {{60}^2}{\omega ^2}{C^2}} \right)\\ {R_x} = \frac{{35}}{4}\;{\rm{\Omega }} \end{array}$$

And, $$60{\omega ^2}C{L_x} = \frac{{35}}{4} \times {60^2}{\omega ^2}{C^2}\;$$

$$\Rightarrow {L_x} = \frac{{35}}{4} \times 60 \times C = \frac{{35}}{4} \times 60 \times 25 \times {10^{ – 6}} = 13.125\;mH$$

$${\rm{Quality\;factor}},{\rm{\;}}Q = \frac{{\omega {L_x}}}{{{R_x}}} = \frac{{2\pi f{L_x}}}{{{R_x}}} = \frac{{2\pi \times 50 \times 13.125 \times {{10}^{ – 3}}\;}}{{\frac{{35}}{4}}} = 0.47$$

14. High voltage Schering bridge is used for the measurement of

1. Resistance and inductance of a coil
2. Frequency of ac source
3. Loss angle of a capacitor
4. Q of a coil

Answer:3. Loss angle of a capacitor

Explanation:

The loss angle is the tangent of the angle by which the current in a lossy capacitor lags the current in an ideal capacitor. The loss angle is also referred to as the dissipation factor or the dielectric loss.

Schering bridge is used for the measurement of capacitance, dissipation factor, and loss angle.

Dissipation factor = tan δ = ω CR

15. Which of the following methods is used to measure medium resistance?

1. Megger
2. Loss of charge method
3. Wheatstone Bridge method
4. Kelvin Double Bridge method

Explanation:

A Wheatstone bridge is an electrical circuit used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component. Wheatstone bridge along with an operational amplifier is used to measure physical parameters such as temperature, light, and strain.

16. The bridge used for the measurement of Inductance is

1. Kelvin bridge
2. Wien bridge
3. Schering bridge
4. Maxwell bridge

Explanation:

Maxwell’s bridge is used to measure the unknown inductance of the circuit by using calibrated resistors and capacitors. This bridge circuit compares the known inductance value with a standard value.

17. Low resistance can be accurately measured by

1. Kelvin Bridge
2. Wheatstone Bridge
3. Wien’s Bridge
4. Schering Bridge

Explanation:

The resistances are classified depending upon the values as:

• The resistances of the order of 1 Ω (or) less than 1 Ω are classified as low resistances.
• The resistances from 1 Ω to 100 KΩ are classified as medium resistances.
• The resistances of the order of 100 KΩ (or) higher are classified as high resistances.

Kelvin’s Double Bridge Method is a modification of the Wheatstone bridge method. Accurate measurement of very low resistance is possible with Kelvin’s Double Bridge Method.

While measuring low resistance value the contact and lead resistance cause significant errors in reading, hence in order to overcome this error kelvin double bridge is used.

18. Which of the following is used to measure value of quality factor below 1?

1. Anderson’s Bridge
2. Maxwell’s Inductance Bridge
3. Hay’s Bridge
4. Wheatstone Bridge

Explanation:

Anderson’s bridge is a bridge circuit used to measure the self-inductance of the coil. It enables the measurement of inductance by utilizing other circuit components like resistors and capacitors. Anderson’s Bridge is used to measure values of inductance and quality factor in a low range of less than 1.

Note:-

• Maxwell’s Inductance Bridge is used to measure only inductance but not for the quality factors.
• Maxwell’s Inductance Capacitance Bridge is used to measure inductance and quality factors below 10.
• Hay’s Bridge is used to measure inductance and quality factors above 10.

19. Kelvin double bridge is best suited for the measurement of

1. Resistances of very low value
2. Low-value capacitance
3. Resistances of very high value
4. High-value capacitance

Answer:1. Resistances of very low value

Explanation:

A kelvin bridge or kelvin double bridge is a modified version of the Wheatstone bridge, which can measure resistance values in the range between 1 to 0.00001 ohms with high accuracy. It is named because it uses another set of ratio arms and a galvanometer to measure the unknown resistance value. Kelvin’s double bridge is used for measuring low values of resistance.

20. Which of the following bridges can be used to measure inductance?

1. Maxwell bridge
2. Anderson bridge
3. Both 1 and 2
4. None of these