Electrical Measurements Question Bank on “Consideration in Selecting Voltmeter”.
1. Input impedance of a voltmeter is ___________
a) high
b) low
c) medium
d) zero
Answer: a
Clarification: In order to prevent the loading effect in a voltmeter, the input impedance is maintained as high as possible. It must be maintained higher than the impedance of the circuit being used.
2. Input impedance depends on _________
a) resistance
b) capacitance
c) inductance
d) voltage
Answer: b
Clarification: Shunt capacitance appearing across the input terminals affects the input impedance. Capacitive reactance of the capacitance is inversely proportional to the frequency.
Xc ∝ 1⁄f
where, Xc is the capacitive reactance
f is the frequency.
3. At high frequencies the capacitive reactance _________
a) is constant
b) increases
c) decreases
d) becomes zero
Answer: c
Clarification: We know that the capacitive reactance is inversely proportional to the frequency.
Xc ∝ 1⁄f
At high frequencies, the capacitive reactance becomes very small.
4. Voltage ranges in a meter are _________
a) 5-10-15
b) 20-50-100
c) 0.5-1-1.5
d) 1-3-10
Answer: d
Clarification: Meter scale will have a calibration of 1-3-10 for the voltage range with a separation of 10 dB. It can also be in the sequence of 1.5-5-15. We can also make use of a single scale.
5. Linear meter with 1% accuracy must have _________
a) 100 divisions
b) 50 divisions
c) 200 divisions
d) 500 divisions
Answer: a
Clarification: In order to recognize a reading with 1% accuracy it must have 100 divisions on the 1 V range.
6. Decibel covers a small range of values.
a) True
b) False
Answer: b
Clarification: As the unit decibel makes of the logarithmic scale, it covers a wide range of values of any given quantity.
7. Noise is a function of _________
a) voltage
b) current
c) bandwidth
d) frequency
Answer: c
Clarification: Noise in general depends on the value of the bandwidth. Voltmeter having a large bandwidth takes up more noise. Usually, the sensitivity of a voltmeter is 1mV for a bandwidth of 10Hz – 10MHz.
8. Current can be measured effectively by making use of _________
a) d.c. voltmeter
b) a.c. ammeter
c) d.c. ammeter
d) a.c. voltmeter
Answer: d
Clarification: By making use of an a.c. voltmeter in series with resistance we can obtain the current value. We can also make use of the current probe method to obtain the value of the current without effectively disturbing the circuit.
9. Average responding voltmeter is cheap and accurate.
a) True
b) False
Answer: a
Clarification: Average responding voltmeter is used for a.c. measurements for a sine wave with 10% distortion or less. Hence the average responding voltmeter is cheap and accurate.
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