Electrical Measurements & Measuring Instruments Multiple Choice Questions on “Introduction to AC Bridges”.
1. In the simplest form, an AC bridge consists of ____________
a) arms, source and a detector
b) arms and source
c) source and detector
d) arms and detector
Clarification: In its simplest form, an AC bridge consists of four arms, a source for excitation and a null detector. The source is connected across a pair of arms while the detector is connected to the pair of opposite arms.
2. Source is ________
a) dc supply
b) ac supply
c) mixed mode supply
d) high voltage supply
Clarification: For an AC bridge we require an AC supply as the source of voltage. It supplies AC voltage at the required frequency.
3. At high frequency, source consists of ________
d) op amps
Clarification: Op amps are basically differential amplifiers. Amplifiers are used in analog circuits for increasing the strength of the signal. Electronic oscillators form sources at high frequencies.
4. Commonly used balance detectors for AC bridges are headphones, tuned amplifiers and vibration galvanometers.
Clarification: Headphones, tuned amplifier circuits and vibration galvanometers are used for detecting the balance condition in AC bridges.
5. What is the frequency range for a headphone as a detector?
a) 20 Hz to 20 kHz
b) 10 kHz to 1 MHz
c) 10 MHz to 1 GHz
d) 250 Hz to 4 kHz
Clarification: Headphones can be used as detectors in AC bridges in the low audio frequency range. Low audio frequency range varies from 250 Hz to 4 KHz.
6. For single frequency value, the most sensitive detector is ________
a) tuned detector
b) vibration galvanometer
Clarification: Vibration galvanometer is used for detecting the balance condition. Oscillator is used as a source of supply voltage. Tuned detector is the most sensitive detector for a single frequency value.
7. Tuned detectors are used in the frequency range of ________
a) 1 Hz to 100 Hz
b) 10 Hz to 100 Hz
c) 1 kHz to 100 kHz
d) 1 MHz to 100 MHz
Clarification: Tuned amplifier circuits are used as detectors in the low frequency range. Low frequency range usually ranges from 10 Hz to 100 Hz in AC bridges.
8. Vibration galvanometers are used for ________
a) very high frequency
b) very low frequency
c) low audio frequency
d) high audio frequency
Clarification: Vibration galvanometers are used as detectors in AC bridges for low audio frequency. Low audio frequency ranges from 5 Hz to 1000 Hz.
9. AC bridge is an outcome of ________
a) Kelvin bridge
c) De Sauty bridge
d) Wheatstone bridge
Clarification: Wheatstone bridge is the simplest form of bridge for the measurement of resistance and forms the basis for an AC bridge. Kelvin bridge is used for the measurement of low resistance and a megger is used for the measurement of high resistances.