A standard cell of 1.0185 V is used with a slide wire potentiometer. The balance

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Question
A standard cell of 1.0185 V is used with a slide wire potentiometer. The balance was obtained at 60 cm. When an unknown emf was connected, the balance was obtained at 82 cm. The magnitude of unknown emf is
Options
A. 1.39 V
B. 0.75 V
C. 13.9 V
D. 7.45 V

Correct Answer

1.39 V

Explanation

A standard cell of 1.0185 V is used with a slide wire potentiometer. The balance was obtained at 60

.

Measurements and Instrumentation problems

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3. In two wattmeter method of 3 phase power measurement, when does one wattmeter read negative
Options
A. when power factor is less than 0.5 lagging
B. when power factor is greater than 0.5 lagging
C. when power factor is less than 0.5
D. when power factor is unity

4. An LVDT is used to measure displacement. The LVDT feeds a Voltmeter of 0-5 V range through a 250 gain amplifier. For a displacement 0.5 mm the output of LVDT is 2 mV. The sensitivity of instrument is
Options
A. 0.1 V/mm
B. 0.5 V/mm
C. 1 V/mm
D. 5 V/mm

5. An ammeter of 0-25 A range has a guaranteed accuracy of 1% of full scale reading. The current measured is 5 A. The limiting error is
Options
A. 2%
B. 2.5%
C. 4%
D. 5%

6. To increase Q factor of a coil, the wire should be
Options
A. long
B. thin
C. thick
D. long and thin

7. The Lissajous pattern observed on screen of CRO is a straight line inclined at 45� to x axis. If X-plate input is 2 sin ?t, the Y-plate input is
Options
A. 2 sin ?t
B. 2 sin (?t + 45�)
C. 2 sin (?t - 45�)
D. 22 sin ?t + 45�)

8. The angle ? for a mica capacitor is about
Options
A. 25�
B. 15�
C. 5�
D. 1�

9. A voltmeter using thermocouples measures
Options
A. rms value
B. peak value
C. average value
D. peak to peak value

10. Which of the following statement is correct for two wattmeters method of power measurement in 3 phase circuit?
Options
A. Power can be measured by this method only for star connected loads
B. When two wattmeters have equal readings power factor is 0.5.
C. When power factor is 1, one of the wattmeters readings is zero
D. When the two wattmeter read equal and opposite, p.f. is zero.

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