Free Bachelor of Electrical Engineering Measurement and Instrumentation Questions and Answers — Questions and Answers

Question 1: Which of the above measuring techniques does a bridge circuit use?

differential
absolute
comparison (Correct answer)
relative

Correct answer: comparison

Bridge circuits, such as the Wheatstone bridge, are primarily used for precise measurement by comparing an unknown electrical quantity (like resistance, capacitance, or inductance) with a known standard. The bridge is balanced when the detector shows no current, indicating that the ratios of the impedances in the arms are equal. This comparison method allows for high accuracy.

Question 2: Which of the following approaches is most frequently used to gauge low resistance?

potentiometer method
ducter ohmmeter method
kelvin double bridge method (Correct answer)
ammeter-voltmeter method

Correct answer: kelvin double bridge method

The Kelvin Double Bridge is specifically designed to accurately measure very low resistances, typically below 1 ohm. It effectively eliminates the errors caused by contact and lead resistances, which are significant when measuring small resistance values, by using a double set of ratio arms. This makes it the preferred method for such measurements.

Question 3: Which of the above techniques is used to test medium resistance?

Anderson Bridge
Direct-Deflection method
Carey-Foster bridge method (Correct answer)
Kelvin’s double bridge method

Correct answer: Carey-Foster bridge method

The Carey-Foster bridge is a modification of the Wheatstone bridge, often used for accurately measuring medium resistances and for comparing two nearly equal resistances. It is particularly effective in minimizing errors due to lead resistances, making it a suitable choice for precision measurements in the medium resistance range.

Question 4: The most sensitive detector for a single frequency value is which one of the following?

headphone
oscillator
vibration galvanometer
tuned detector (Correct answer)

Correct answer: tuned detector

A tuned detector, such as a tuned amplifier or a resonant circuit, is designed to be highly sensitive to a specific frequency while rejecting others. This makes it the most sensitive choice for detecting a signal at a single, known frequency in bridge circuits or communication systems, as it can filter out noise and interference.

Question 5: Which of the following describes an equilibrium for a bridge?

When power dissipation is high
When no current flows (Correct answer)
When no voltage drop across the circuit
When the temperature of the circuit is high

Correct answer: When no current flows

A bridge circuit is said to be in equilibrium (or balanced) when the potential difference between two specific points in the bridge is zero. This condition results in no current flowing through the detector connected between these points. At balance, the unknown component's value can be determined from the known values of the other bridge arms.

Question 6: The method of ________ yields an unknown capacitance value.

using a tuned detector
comparison with standard (Correct answer)
using a vibration galvanometer
using capacitance of other ratio arms

Correct answer: comparison with standard

Similar to resistance bridges, capacitance bridges (like the Schering bridge or Wien bridge) determine an unknown capacitance by comparing it against a known, standard capacitor. The bridge is balanced by adjusting known components until the detector shows no current, allowing the unknown capacitance to be calculated from the ratio of the known values.

Question 7: Which of the following is an equation of balance to calculate resistance?

R1 = R2 R3⁄R4 (Correct answer)
R1 = R2 ⁄ R4
R1 = R3 ⁄ R4
R1 = R2 R3

Correct answer: R1 = R2 R3⁄R4

This equation, R1 = R2 * R3 / R4, represents the balance condition for a Wheatstone bridge. When the bridge is balanced, the ratio of resistances in one arm equals the ratio in the other arm (R1/R2 = R3/R4). Rearranging this equation allows for the calculation of an unknown resistance (R1) based on three known resistances.

Question 8: By _________, inductance control is attained.

using Lx
using R2 (Correct answer)
using R4
using R5

Correct answer: using R2

In many AC bridge circuits used for inductance measurement, such as the Maxwell or Hay bridge, the unknown inductance (Lx) is balanced by adjusting a variable resistance in one of the bridge arms. Often, this variable resistance is denoted as R2, which directly influences the balance equation for inductance. Thus, adjusting R2 allows for control and measurement of inductance.

Question 9: The following situations call for the usage of a Schering bridge:

measuring currents
measuring voltages
testing capacitors (Correct answer)
protecting the circuit from temperature rises

Correct answer: testing capacitors

The Schering bridge is a specialized AC bridge circuit primarily used for the precise measurement of capacitance and dissipation factor (or power factor) of capacitors. It is particularly useful for testing high-voltage capacitors and for determining dielectric losses, making it an essential tool for capacitor characterization.

Question 10: What relationship does the balance equation have to frequency?

independent (Correct answer)
varies by a factor of 2
depends on the supply magnitude
depends on the detector used

Correct answer: independent

For many AC bridge circuits, particularly those designed for measuring resistance or capacitance, the balance equation is independent of the supply frequency. This means that once the bridge is balanced, it remains balanced regardless of the frequency of the AC source. This characteristic simplifies measurements and ensures accuracy across different frequencies for these specific bridge types.

Question 11: The protecting arm is which of the following?

resistance R
capacitance C
series RC combination
parallel RC combination (Correct answer)

Correct answer: parallel RC combination

A protecting arm in electrical measurement circuits, such as AC bridges, is designed to minimize the impact of stray capacitances and leakage currents. It typically consists of a parallel combination of resistance (R) and capacitance (C). This configuration provides a controlled path for unwanted currents, diverting them away from the main measurement arms and thereby improving the accuracy and stability of the bridge balance.

Question 12: What may be measured using Maxwell's Inductance Capacitance Bridge?

Inductance (Correct answer)
Capacitance
Frequency
Mutual Inductance

Correct answer: Inductance

Maxwell's Inductance Capacitance Bridge is a specific type of AC bridge circuit primarily used for the precise measurement of unknown inductance. It operates by comparing the unknown inductance with a known standard capacitance. This bridge is particularly well-suited for measuring inductors with a medium Q-factor, providing accurate results by balancing the reactive components.

Question 13: The definition of a multiplier is

resistive
non-inductive (Correct answer)
capacitive
non-capacitive

Correct answer: non-inductive

In electrical measurement, a multiplier is a high resistance connected in series with a voltmeter to extend its voltage range. For accurate readings, especially with alternating current (AC) voltages, it is crucial that this resistance is non-inductive. Any significant inductance would introduce undesirable phase shifts and impedance changes with frequency, leading to errors in the voltage measurement.

Question 14: A C.T.'s windings are

grounded
tied together
shorted
wound over one another (Correct answer)

Correct answer: wound over one another

A Current Transformer (CT) is designed to accurately step down high currents to lower, measurable values. Its primary and secondary windings are constructed by winding them over one another, often concentrically, around a common magnetic core. This close coupling ensures efficient magnetic flux linkage between the windings, which is essential for accurate current transformation and reliable operation.

Question 15: What relationship does the voltage ratio have with frequency?

they oppose each other (Correct answer)
they aid each other
depends on the setup of the circuit
they are independent of each other

Correct answer: they oppose each other

In many real-world electrical systems, such as transformers or filters, the voltage ratio can be inversely affected by frequency, meaning they oppose each other. For instance, in a practical transformer, as frequency increases beyond its design range, factors like leakage inductance and winding capacitance become more significant. This can lead to increased losses and a reduction in the effective voltage ratio (secondary voltage to primary voltage), thus decreasing efficiency at higher frequencies.

Question 16: Raising the second burden ______

increases Is (Correct answer)
decreases Is
keeps Is constant
decreases Ip

Correct answer: increases Is

In the context of a Current Transformer (CT), 'burden' refers to the load impedance connected to its secondary winding. If 'raising the second burden' is interpreted as increasing the power demand from the secondary circuit (VA rating), then the secondary current (Is) must increase to deliver that higher power. This assumes the CT is operating within its linear range and is capable of supplying the increased current without saturating, which would otherwise cause Is to decrease relative to the ideal ratio.

Free Bachelor of Electrical Engineering Measurement and Instrumentation Questions and Answers

Which of the above measuring techniques does a bridge circuit use?