Electric Circuits Questions and Answers – Measuring Resistance the Wheatstone Bridge and Delta-to-Wye (Pi-to-Tee) Equivalent Circuits

This set of Electric Circuits Questions and Answers focuses on “Measuring Resistance the Wheatstone Bridge and Delta-to-Wye (Pi-to-Tee) Equivalent Circuits”.

1. The Wheatstone Bridge is mainly used to measure ______________
a) Currents
b) Voltages
c) Node potentials
d) Resistances
View Answer

Answer: d
Explanation: Resistances can be measured by various methods. Wheatstone bridge is one such method. In this method resistances in the range of 1Ω to 1 MΩ can be measured.

2. The relation between the resistances in the given Wheatstone bridge circuit is _____________
The relation between the resistances in the given Wheatstone bridge circuit is P/Q = R/S
a) P/S = R/Q
b) PR = QS
c) P/Q = R/S
d) PQ = RS
View Answer

Answer: c
Explanation: The relation is P/Q=R/S or PS=QR.

3. Find the unknown resistance value in given circuit.
The unknown resistance value in given circuit is 10.2Ω
a) 10.2Ω
b) 11.7Ω
c) 10.5Ω
d) 11.5Ω
View Answer

Answer: a
Explanation: A/B=C/D. Using this D= 10.2Ω.
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4. Lower resistances are difficult to measure using Wheatstone bridge circuit because of ____________
a) Leakage currents
b) I2R effects
c) Power dissipation
d) Thermal breakdown
View Answer

Answer: b
Explanation: A standard Wheatstone bridge couldn’t measure lower resistances because of thermoelectric voltages which are generated at the junctions of the dissimilar metals and also because of thermal heating effects- that is, i2R effects.

5. If P/Q=1, unknown resistance S=1000Ω and R could be varied from 0 to 100Ω then the bridge could be ___________
a) A balanced circuit
b) A rectified circuit
c) An unbalanced circuit
d) An identical circuit
View Answer

Answer: c
Explanation: P/Q=R/S. If P/Q=1 then according to given range of R and S, the bridge circuit could never be a balanced one.
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6. The other name for Delta connection is ___________
a) Star connection
b) Pi connection
c) T connection
d) Y connection
View Answer

Answer: b
Explanation: Delta connection is also known as Pi connection because the ∆ can be shaped into π without disturbing the electrical equivalence of both the structures.

7. Star connection can also be called as Y (or) T connection.
a) True
b) False
View Answer

Answer: a
Explanation: Star connection can also be called as Y (or) T connection because the star can be shaped into Y or T without disturbing the electrical equivalence of both the structures.
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8. If R2 = RC RA / (RA +RB +RC ) then R3 equals?
a) RA RB / (RA +RB +RC )
b) RC RA / (RA +RB +RC )
c) RB RC / (RA +RB +RC )
d) RX RA / (RA +RB +RC )
View Answer

Answer: a
Explanation: R3 = RA RB / (RA +RB +RC ).

9. Convert the given Delta circuit to star circuit and give the Ra , Rb and Rc values.
The Ra, Rb & Rc values are Ra=4Ω, Rb=4.30Ω & Rc=4.66Ω by using the standard formulae

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a) Ra=5Ω, Rb = 4.5Ω, Rc=4.67Ω
b) Ra=4Ω, Rb=4.30Ω, Rc=4.66Ω
c) Ra=3Ω, Rb=4Ω, Rc =5Ω
d) Ra=5.2Ω, Rb=4.2Ω, Rc =4.89Ω
View Answer

Answer: b
Explanation: By using the standard formulae the delta circuit can be converted into star circuit.

10. Find VAB if iAB = 5A.
The VAB is 34.21V if iAB = 5A by converting the star circuits into the delta
a) 32.76V
b) 35.56V
c) 36.12V
d) 34.21V
View Answer

Answer: d
Explanation: By converting the star circuits into the delta and then measuring the equivalent resistance, voltage value can be calculated using this resistance and the given current value.

11. Convert the given star network into Pi network and calculate the sum of all the resistances in the obtained Pi network.
Sum of all resistances in obtained Pi network is 122.5Ω for star network into Pi network
a) 125.5Ω
b) 122.5Ω
c) 127.8Ω
d) 129.8Ω
View Answer

Answer: b
Explanation: Conversion of given network into delta gives the resistances.
After that sum of the resistances equals 122.5Ω.

12. The star and delta networks would be electrically equal if resistances measured between any pair of terminals __________
a) Is different
b) Greater in star
c) Greater in delta
d) Is equal
View Answer

Answer: d
Explanation: The star and delta networks would be electrically equal if a resistance measured between any pair of terminals is same.

13. A Wheatstone bridge is balanced when the galvanometer shows __________ reading.
a) 0A
b) 1A
c) Infinity
d) -1A
View Answer

Answer: a
Explanation: A Wheatstone bridge is balanced when the galvanometer shows 0A reading when resistors obey P/Q=R/S.

14. __________ are difficult to measure using Wheatstone bridge.
a) Higher resistances
b) Currents
c) Lower resistances
d) Voltages
View Answer

Answer: c
Explanation: Specifically Kelvin Bridge is used for measuring lower resistances.

15. What will be the resistance between B and C when the network given below is converted into delta?
The resistance between B & C when network is converted into delta is 8.66Ω
a) 13Ω
b) 8.66Ω
c) 6.5Ω
d) 7.33Ω
View Answer

Answer: b
Explanation: Resistance between B and C = 2+4+ ((2*4)/3).

Sanfoundry Global Education & Learning Series – Electric Circuits.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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