VIGNAN’S UNIVERSITY :: VADLAMUDIEE216 - Electrical Measurements & Instrumentation (EM&I)

UNIT – IV (MID-III)Question Bank

Measurement of Resistance, Inductance and Capacitance1Mark Questions

1. Loss of charge method is used to measure:

a) Capacitance b) Low Resistance c) Medium Resistance d) High Resistance

2. Measurement of low resistance is done by:

a) Kelvin’s double bridge b) Wheatstone bridge c) Meggar d) Schering bridge

3. Mention the application of Carey foster slide Wire Bridge.

4. Mention one limitation of Wheatstone bridge.

5. Mention one difficulty in measuring high resistance.

6. Wheatstone bridge is a ________________ type of instrument

a) Integrating b) Indicating c) Recording d) None

7. Measurement of Inductance is done by:

a) Max well’s bridge b) De Sauty’s bridge c) Schering bridge

8. What is the range of medium resistance?

9. Name the methods used for low resistance measurement.

10. Name the methods used for medium resistance measurement

11. Where high resistance measurement is required?

12. Why megh ohm method is used?

13. What is the range of low resistance?

14. What is the range of medium resistance?

15. Which range resistance is measured in direct deflection method?

16. State the balance equation used in bridge methods.

17. State the use of ac bridges.

18. Name the bridge circuits used for the measurement of self-inductance.

19. Name the bridge circuits used for the measurement of capacitance.

20. Name the bridge circuits used for the measurement of mutual inductance.

21. Define Q-factor of the coil.

2 Mark Questions

1. Mention the applications of D.C potentiometers.

2. Mention the applications of A.C potentiometers.

3. State the advantages of Wheatstone bridge method.

4. State the advantages of Kelvin double bridge method.

5. Which type of detector is used in ac bridges?

6. Name the sources of errors in ac bridge measurements.

7. State the advantages of Maxwell’s bridge.

8. State the disadvantage of Maxwell’s bridge.

9. State the disadvantages of Hay’s bridge.

10. State the use of Wein’s bridge.

11. What is the use of Owen’s bridge?

12. What is the use of Schering’s bridge?

13. Disadvantages of Schering’s bridge.

14. How leakage errors are minimized in ac bridge circuits.

15. Why is De-Sauty’s bridge used?

16. What is the use of Anderson’s bridge?

17. Write the advantages and disadvantages of Anderson’s bridge.

5 Mark Questions

1. Explain the operation of Kelvins double bridge for measuring low resistance. Derive

relevant equations. Why there is no phasor diagram for Kelvins double bridge.

2. Derive the equations of balance for an Anderson’s bridge. Draw the phasor for

conditions under balance. Discuss the advantages and disadvantages of the bridge.

3. Explain the Megh-ohm method with the aid of a neat diagram.

4. Show that the connecting effect of lead resistance during the measurement of

unknown resistance can be nullified in Kelvin double bridge.

5. Derive the sensitivity of Wheat stone’s bridge used for measuring unknown

resistance.

6. Describe how an unknown capacitance and loss angle can be measured using Desauty’s

bridge with the help of phasor diagram and also derive the necessary expressions for it.

7. Explain ammeter voltmeter method and substitution method for measuring unknown

resistance.

8. Derive the unknown inductance in Owen’s bridge.

9. Derive the equation of balance for Desauty bridge.

10. A Kelvin bridge is balanced with the following constants: Outer ratio arms 100Ω

and 1000 Ω: Inner ratio arms 99.92 Ω and 1000.6 Ω; Resistance of link 0.1 Ω;

standard resistance 0.00377 Ω. Calculate the value of unknown resistance.

10 Mark Questions

1. a. An ac bridge with terminals A,B,C,D (consecutively marked) has in arm AB, a pure

resistance; arm BC a resistance of in parallel with a capacitor of 0.5μF; arm CD, a

resistance of 400Ω in series with a capacitor of 1.0μF; and arm DA, a resistance of

1000Ω

(i) Obtain the value of the frequency for which the bridge can be balanced

(ii) Calculate the value of resistance in arm AB to produce balance.

b. Explain about loss of charge method of measuring high resistance.

2. a. Explain how Wein Bridge can be used to determine the frequency in terms of

values of its various elements.

b. Why wheat stone bridge is not suitable for measurement of low resistances?

Explain how you can overcome these by using Kelvin’s double bridge.

3. a. Explain any one method of measuring high resistance.

b. Derive the expressions for unknown inductance and resistance of a coil using

Hay’s bridge. Hay’s bridge is suitable for measuring high Q coils. Explain.

4. a. Describe how Schering Bridge can be used for measurement of an unknown

capacitance and its loss angle. Derive the conditions of balance.

b. In a Carey Foster bridge a resistance of 1.0125Ω is compared with a standard

resistance of 1.00000Ω.The slide wire has a resistance of 0.250Ω in 100

divisions .The arms are normally each 10Ω are actually 10.05Ω and 9.95Ω

respectively. How far are the balance positions from those which would obtain

if ratio arms were true to their nominal value? The slide wire is 100 cm long.

5. a. Derive an expression for the measurement of unknown inductance using

Anderson Bridge. Also give the corresponding vector diagram.

b. Derive an expression for the measurement capacitance and dissipation factor of

modified Desauty’s Bridge along with its vector diagram.

6. a. The value of a high resistance is measured by loss of charge method. A Capacitor

having a capacitance of 2.5 µF is charged to a potential of 500 V D.C and is

discharged through the high resistance. An electrostatic voltmeter, kept across the high

resistance, reads the voltage as 300 V at the end of 60 Seconds. Calculate the value of

high resistance.

b. With the help of circuit diagram explain how capacitance can be measured by the use

of a Schering bridge.

7. a. The four arms of an ac bridge network are as follows: arm AB: an Unknown

impedance; arm BC : a standard capacitor of 1000 pF; arm CD: a non-inductive

resistor of 100Ω in parallel with a capacitor of 0.01µF; arm DA : a non-inductive

resistor of 1000Ω. The A.c supply is connected across terminals B, D and the supply

frequency is 50 Hz. If the bridge is balanced with the above values, calculate the

components of the unknown impedance.

b. Write short notes on detectors in ac bridges

8. a. A supply of 450Hz is given between terminals A and C and the detector is connected

between b & d. At balance R2=4.8 Ω, R3=2 KΩ, R4=2.85 KΩ, C2=0.5 μ & r2=0.4 Ω.

Calculate the value of C1, r1& also calculate dissipation factor of this capacitor.

b. Draw the diagram of a laboratory type (Crompton’s) d.c. potentiometer. What do you

mean by standardization of potentiometer?

9. a. How can potentiometer be used for

i) Calibration of a voltmeter ii) Calibration of a wattmeter

b. The four arms of a bridge are: AB: An imperfect capacitor C1 with an equivalent

series resistance r1, BC: a non-inductive resistance R3, CD: a non-inductive resistance

R4, DA: an imperfect capacitor C2 with equivalent series resistance r2, series with a

resistance R2. The A.c supply is connected across terminals B, D and the supply

frequency is 50 Hz. If the bridge is balanced, calculate the value of C2