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- Question
The coil of a moving iron instrument has a resistance of 500 ? and an inductance of 1 H. It reads 250 V when a 250 V dc is applied. If series resistance is 2000 ?, its reading when fed by 250 V, 50 Hz ac will be
Options- A. 260 V
- B. 252 V
- C. 250 V
- D. 248 V
- Correct Answer
- 248 V
Explanation
Measurements and Instrumentation problems
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- 1. In a CRO which of the following is not a part of electron gun
Options- A. cathode
- B. grid
- C. accelerating anode
- D. X - Y plates Discuss
Correct Answer: X - Y plates
Explanation:
Electron gun consists of cathode, grid and accelerating anode.- 2. 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. Discuss
Correct Answer: When the two wattmeter read equal and opposite, p.f. is zero.
Explanation:
When p.f. is zero, active power is zero and the two redaings are equal and opposite.- 3. A voltmeter using thermocouples measures
Options- A. rms value
- B. peak value
- C. average value
- D. peak to peak value Discuss
Correct Answer: rms value
Explanation:
Since the thermocouple is based on heating effect, rms value is measured.- 4. The angle ? for a mica capacitor is about
Options- A. 25°
- B. 15°
- C. 5°
- D. 1° Discuss
Correct Answer: 1°
Explanation:
Mica capacitor has very low loss and loss angle ? is very very small.- 5. 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°) Discuss
Correct Answer: 2 sin ?t
Explanation:
When signals to X and Y plates are in phase, the display is a straight line inclined at 45°.- 6. In a ballistic galvanometer, a charge of 100 ?C gives a first swing of 25°. The charge required to cause first swing of 50° is
Options- A. 200 ?C
- B. 400 ?C
- C. 50 ?C
- D. 25 ?C Discuss
Correct Answer: 400 ?C
Explanation:
swing is proportional to charge.- 7. In a strain measuring device using a strain gauge, the output quantity is
Options- A. voltage
- B. resistance
- C. impedance
- D. either (a) or (b) Discuss
Correct Answer: voltage
Explanation:
The measurement is done using an unbalanced bridge.- 8. Magnetic flux density has the dimensions
Options- A. MI-1T-2
- B. M-1I-2T-2
- C. ML-3T-2
- D. MI-1T-3 Discuss
Correct Answer: MI-1T-2
Explanation:
Flux density = flux/area.- 9. A dynamometer wattmeter is connected in ac circuit. The measured power is
Options- A. rms power
- B. average power
- C. peak power
- D. instantaneous power Discuss
Correct Answer: average power
Explanation:
All wattmeters measure average power over a cycle.- 10. A meter with a resistance of 100 ? and a full scale deflection of current of 1 mA is to be converted into voltmeter of 0 - 5 V range. The multiplier resistance should be
Options- A. 490 ?
- B. 5000 ?
- C. 4900 ?
- D. 5100 ? Discuss
Correct Answer: 4900 ?
Explanation:
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