Electrical Measurements & Measuring Instruments Multiple Choice Questions on “Schering Bridge”.

1. Schering bridge is one of the most widely used AC bridges.

a) True

b) False

Answer: a

Clarification: Schering bridge is an AC bridge used for the measurement of unknown capacitance, dielectric loss and power factor. It is one of the most commonly used AC bridges.

2. Schering bridge is used for _________

a) low voltages only

b) low and high voltages

c) high voltages only

d) intermediate voltages only

Answer: b

Clarification: Schering bridge is used for both low as well as high voltages. A particular bridge connection is used for low voltage. High voltages employ the use of a different type of Schering bridge.

3. Power factor of a Schering bridge is _________

a) p.f. = sin∅_{x} = ^{Zx}⁄_{Rx}

b) p.f. = cot∅_{x} = ^{Rx}⁄_{Zx}

c) p.f. = cos∅_{x} = ^{Rx}⁄_{Zx}

d) p.f. = tan∅_{x} = ^{Rx}⁄_{Zx}

Answer: c

Clarification: The power factor of the RC combination in a Schering bridge is given by the relation p.f. = cos∅_{x} = ^{Rx}⁄_{Zx}.

where,

R_{x} is the series resistance

Z_{x} is the series impedance comprising of Rx and C_{x}.

4. For phase angles close to 90°, the power factor of the bridge is _________

a) p.f. = ωR_{x}

b) p.f. = ωC_{x}

c) p.f. = R_{x} C_{x}

d) p.f. = ωR_{x} C_{x}

Answer: d

Clarification: When phase angle reaches 90°, reactance equals the impedance and the power factor of the bridge is calculated using the relation,

5. For a series RC circuit, what is δ?

a) voltage between series RC combination and C

b) voltage between series RC combination

c) voltage across C

d) voltage across R

Answer: a

Clarification: In a series RC circuit, δ refers to the angle between the series combination of R_{x}, C_{x} and the voltage across the capacitance C_{x}. δ is also known as the loss angle.

6. What is the expression for the loss angle?

a) tan δ = ωR_{4}

b) tan δ = ωR_{4} C_{4}

c) tan δ = ωC_{4}

d) tan δ = R_{4} C_{4}

Answer: b

Clarification: The expression for the loss angle can be computed as the ratio of the tangent of the voltage drop across resistance R_{x} to the voltage drop across the capacitance C_{x}.