Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE) PDF Download

Q1: A balanced Wheatstone bridge ABCD has the following arm resistances:
RAB = 1kΩ ± 2.1 is an unknown resistance; RDA = 300Ω ± 0.4. The value of RCD and its accuracy is   (2022)
(a) 30Ω ± 3Ω
(b) 30Ω ± 0.9Ω
(c) 3000Ω ± 90Ω
(d) 3000Ω±3Ω3000Ω ± 3Ω
Ans:
(b)
Sol: The condition for balanced bridge
RABRCD = RDARBC
Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)∴ RCD = 30 ± 30 x (3/100) = 30 ± 0.9Ω

Q2: Inductance is measured by  (2021)
(a) Schering bridge
(b) Maxwell bridge
(c) Kelvin bridge
(d) Wien bridge
Ans: 
(b)
Sol: Maxwell's bridge is used for measurement of inductance.
Wein's bridge is used for measurement of frequency
Kelvin's bridge is used for measurement of low value of resistance.
Schering bridge is used for measurement of capacitance, dilectric loss and permittivity etc.

Q3: In the bridge circuit shown, the capacitors are loss free. At balance, the value of capacitance C1 in microfarad is ______.  (SET-3 (2014))
Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)(a) 0.1
(b) 0.2
(c) 0.3
(d) 0.4
Ans: 
(c)
Sol: Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)Redrawing the given bridge circuit, we have:
Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)Z4 = 105 kΩ
At balance, current through galavanometer:
Ig = 0
and ∣Z1∣∣Z4∣ = ∣Z2∣∣Z3
Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)= 0.3μF

Q4: The reading of the voltmeter (rms) in volts, for the circuit shown in the figure is _________   (SET-1 (2014))
Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)(a) 80.32
(b) 141.42
(c) 160.45
(d) 180.78
Ans: 
(b)
Sol: Given bridge is shown in figure
Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)From the given bridge circuit, we see that product of opposite arm impedance are equal
i.e. (−j) × (−j) = (j)(j)
or −1 = −1
Hence, the bridge is balanced, i.e. no current flows through the voltage source V.
vi(t) = 100 sin ωt
Now, = (100/√2) Volt (rms value)
∴ Net current supplied by the source is
Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)Zeq = 0(i.e. net impedance of whole bridge = 0)
Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)Current flow through each parallel path of the bridge circuit, therefore V = V− Vb
Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)= −jI = −j141.42 volt (rms value)
∴ Reading of the voltmeter in volt (rms)
=V = Vab = 141.42

Q5: Three moving iron type voltmeters are connected as shown below. Voltmeter readings are V, V1 and V2 as indicated. The correct relation among the voltmeter readings is   (2013)
Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)(a) Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)

(b) V=V1+V2V = V1 + V2
(c) V = V1V 
(d) V=V2V1V = V− V1 
Ans:
(d)
Sol: V1 = -|j1Ω| x I
V2 = -|j2Ω| x I
V = -j1Ω| x I + j2Ω| x I
= V2 - V1

Q6: The bridge method commonly used for finding mutual inductance is  (2012)
(a) Heaviside Campbell bridge
(b) Schering bridge
(c) De Sauty bridge
(d) Wien bridge
Ans:
(a)
Sol: Heaciside Campbell bridge method is commonly used for finding mutual inductance.

Q7: A lossy capacitor Cx, rated for operation at 5 kV, 50 Hz is represented by an equivalent circuit with an ideal capacitor Cp in parallel with a resistor Rp. The value Cis found to be 0.102 μF and value of Rp = 1.25MΩ. Then the power loss and tan δ of the lossy capacitor operating at the rated voltage, respectively, are  (2011)
(a) 10 W and 0.0002
(b) 10 W and 0.0025
(c) 20 W and 0.025
(d) 20 W and 0.04
Ans: 
(c)
Sol: CP = 0.102 μF
RP = 1.25 MΩ
Power loss = Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)
= 20 W
tanδ  = RIX = (1/ωCPRP)
Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)= 0.025

Q8: The bridge circuit shown in the figure below is used for the measurement of an unknown element ZX. The bridge circuit is best suited when ZX is a  (2011)
Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)(a) low resistance
(b) high resistance
(c) low Q inductor
(d) lossy capacitor
Ans:
(b)
Sol: The bridge is Maxwell bridge.
Element is an inductor.
Inductance = Lx effective resistance of the inductor = Rx
Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)The bridge is limited to measurement of low Q inductor (1 < Q < 10).
It is clear from equation (i) that the measurement of high Q coils demands a large value of resistance R1, perhaps 105 or 106Ω. The resistance boxes of such high value are very expensive. Thus for value of Q > 10, the bridge is unsuitable.
The bridge is also unsuited for coils with a very low value of Q(i.e. Q < 1).

Q9: The Maxwell's bridge shown in the figure is at balance. The parameters of the inductive coil are.  (2010)
Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)(a) R = R2R3/R4, L = C4R2R3 
(b) L=R2R3/R4,R=C4R2R3L = R2R3/R4, R = C4R2R3 
(c) R = R4/R2R3, L = C4R2R3
(d) L = R4/R2R3, R = 1/(C4R2R3)
Ans: 
(a)
Sol: Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)Z1 = R + jωL
Z2 = R2
Z3 = R3
Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)At balance,
Z1Z= Z2Z3
Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)R4(R + jωL) = R2R3(1 + jωC4R4)
RR4 + jωLR4 = R2R+ jωR2R3R4C4
Equating real and imaginary terms
RR4 = R2R3
Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)ωLR4 = ωR2R3R4C4
L = R2R3C4

Q10: The ac bridge shown in the figure is used to measure the impedance Z.
Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE) If the bridge is balanced for oscillator frequency f = 2 kHz, then the impedance Z will be  (2008)
(a) (260 + j0) ω
(b) (0 + j200) ω
(c) (260 - j200) ω
(d) (260 + j200)  ω
Ans:
(a)
Sol: Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)ZAB = 500Ω
ZCD = Z  
ZBC = RBC + (1/jωc)
Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)ZBC = 300 − j200Ω
ZAD = RAD + jωL
ZAD = 300 + j2π × 2 × 10× 15.91 × 10−3
= 300 + j200Ω
At balance,
ZAB × ZCD = ZBC × ZAD
ZCD = Z
Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)Z = (260 + j0)Ω

Q11: A bridge circuit is shown in the figure below. Which one of the sequence given below is most suitable for balancing the bridge?  (2007)
Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)(a) First adjust R4, and then adjust R1
(b) First adjust R2, and then adjust R3
(c) First adjust R2, and then adjust R4
(d) First adjust R4, and then adjust R2
Ans:
(c)
Sol: Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)z1 = R+ jx= R1+jωL1
z= R2
z3 = R3
z4 = R4 − jx4 = R−  (j/ωC4)
Under balanced condition
z1z4 = z2z3
(R+ jωL1)(R− jx4) = R2R3
Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)Equating real and imaginary terms, we obtain
Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)Solving above equations, we get
Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)Q-factor of the coil Q = Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)
Therefore, Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)For a value of a greater than 10, the term (1/Q)2 will be smaller than 1/1000 and can be neglected. Therefore equation (i) and (ii) reduces to
L1 = R2R3C...(iii)
R1 = ω2R2R3R4C24 ...(iv)
R4 appears only in equation (iv) and R2 appears in both equation (iii) and (iv).
So first R2 is adjusted and then R4 is adjusted.

Q12: The items in Group-I represent the various types of measurements to be made with a reasonable accuracy using a suitable bridge. The items in Group-II represent the various bridges available for this purpose. Select the correct choice of the item in Group-II for the corresponding item in Group-I from the following  (2003)
Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE)(a) P = 2, Q = 3, R = 6, S = 5
(b) P = 2, Q = 6, R = 4, S = 5
(c) P = 2, Q = 3, R = 5, S = 4
(d) P = 1, Q = 3, R = 2, S = 6
Ans:
(a)
Sol: Wheat stone bridge is used for measurement of medium resistance.
Kelvin double bridge is used for meserement of low resistance.
Schering bridge is used for meserement of low value of capacitances.
Wein's bridge is used for meserement of the frequency
Hay's bridge is used for meserement of inductance of a coil with a large time-constant.
Carey-foster bridge is used for comparision of resistances which are nearly equal.

The document Previous Year Questions- A.C. Bridges | Electrical and Electronic Measurements - Electrical Engineering (EE) is a part of the Electrical Engineering (EE) Course Electrical and Electronic Measurements.
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FAQs on Previous Year Questions- A.C. Bridges - Electrical and Electronic Measurements - Electrical Engineering (EE)

1. What are the main types of A.C. bridges used in electrical engineering?
Ans. The main types of A.C. bridges used in electrical engineering include the Maxwell Bridge, Schering Bridge, and Wien Bridge. Each of these bridges is designed for specific applications, such as measuring inductance, capacitance, or frequency.
2. How does a Maxwell Bridge work in measuring inductance?
Ans. A Maxwell Bridge measures inductance by balancing a wheatstone-like circuit involving an inductor (unknown), a known resistance, and a known capacitance. By adjusting the bridge until the voltage across the galvanometer is zero, the inductance can be calculated using the known values and the bridge formula.
3. What is the significance of using A.C. instead of D.C. in bridge circuits?
Ans. A.C. is used in bridge circuits because it allows for the measurement of reactance in addition to resistance. This makes it possible to measure components like capacitors and inductors, which have behavior that varies with frequency, something D.C. cannot adequately address.
4. What are the advantages of using A.C. bridges over traditional D.C. bridges?
Ans. The advantages of using A.C. bridges include higher sensitivity and accuracy in measuring reactive components, the ability to measure at different frequencies, and reduced effects of stray capacitance and inductance, which can influence measurements in D.C. circuits.
5. How do you calculate the unknown component in a Schering Bridge setup?
Ans. In a Schering Bridge, the unknown capacitance can be calculated by balancing the bridge and using the formula Cx = (C1 * R2) / (R1 * C2), where Cx is the unknown capacitance, C1 and C2 are known capacitances, and R1 and R2 are the resistances in the bridge circuit.
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