section 1 measurement

1. To increase Q factor of a coil, the wire should be

A.

long

B.

thin

C.

thick

D.

long and thin

Answer & Explanation

Answer: Option C

Explanation:

Q is high if resistance is low. Therefore, wire should be thick.

2. 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

A.

2%B.

2.5%

C.

4%D.

5%

3. The coil of a moving iron instrument has a resistance of 500 Ω and an inductance of 1 H. It reads 250 V when a 250 V dc is applied. If series resistance is 2000 Ω, its reading when fed by 250 V, 50 Hz ac will be

A.

260 V

B.

252 V

C.

250 V

D.

248 V


Answer: Option D

Explanation:

4. In 3 phase power measurement by two wattmeter method, the reading of one wattmeter is zero. The power factor of load is

A. 1 B. 0.5

C. 0 D. 0.8


Answer: Option B

Explanation:

When p.f. = 0.5, 0 = 60° and one of the wattmeters reads zero.

5. In a CRO which of the following is not a part of electron gun

A.

cathode

B.

grid

C.

accelerating anode

D.

X - Y plates


Answer: Option D

Explanation:

Electron gun consists of cathode, grid and accelerating anode.

6. If reference sound pressure P0 is 2 x 10-5 N/m2, a sound pressure of 90 dB is equal to

A.

0.632 N/m2

B.

0.707 N/m2

C.

0.835 N/m2

D.

0.925 N/m2


Answer: Option A

Explanation:

.

7. Which of the following voltmeters would you use for measuring voltage across 20 kΩ resistance?

A.

Voltmeter having a resistance of 5 kΩ

B.

Voltmeter having a sensitivity of 1 kW/V

C.

Voltmeter having sensitivity of 10 kW/V

D.

None of the above


Answer: Option C

Explanation:

Resistance of voltmeter should be very high as compared to 20 kΩ.

8. A single phase energy meter has the rating 1200 resolutions/ kWh. If a 500 W electric gadget is used for 4 hours, the energy meter will make

A.

1200 revolutions

B.

1800 revolutions

C.

2100 revolutions

D.

2400 revolutions


Answer: Option D

Explanation:

0.5 x 4 = 2 kWh = 2 x 1200 revolutions.

9. Assertion (A): De sauty's bridge is suitable only for pure capacitor.

Reason (R): Capacitors are mostly perfect.

A. Both A and R are true and R is correct explanation of A

B. Both A and R are true but R is not correct explanation of A

C. A is true R is false

D. A is false R is true


Answer: Option C

Explanation:

Capacitors are mostly imperfect.

10. In which of the transformer is the secondary nearly short circuited under normal operating conditions?

A.

CT

B.

PT

C.

Distribution transformer

D.

Power transformer


Answer: Option A

Explanation:

CT is operated with secondary short-circuited otherwise a high emf would be induced across

secondary. 11. A moving coil instrument has a resistance of 0.6 Ω and full scale deflection at 0.1 A. To convert it

into an ammeter of 0-15 A range, the resistance of shunt should be

A.

0.6 Ω

B.

0.06 Ω

C.

0.1 Ω

D.

0.004 Ω


Answer: Option D

Explanation:

.

12. A piezoelectric force transducer has a charge sensitivity of 20 pC/N. It is connected to a charge amplifier and overall gain of transducer and amplifier is 50 mV/N. The gain of amplifier is

A.

1 mV/pC

B.

1.5 mV/pC

C.

2.5 mV/pC

D.

4 mV/pC


Answer: Option C

Explanation:

13. 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

A.

0.1 V/mm

B.

0.5 V/mm

C.

1 V/mm

D.

5 V/mm


Answer: Option C

Explanation:

Final output = 2 x 10-3 x 250 = 0.5 V.

.

14. Assertion (A): When a wattmeter is used for low impedance loads, the pressure coil is connected across the load.

Reason (R): A wattmeter measures apparent power.

A. Both A and R are true and R is correct explanation of A

B. Both A and R are true but R is not correct explanation of A

C. A is true R is false



Answer: Option C

Explanation:

Wattmeter measures active power.

15. As per BIS there are 6 accuracy classes of instruments.

A.

TrueB.

False


Answer: Option B

Explanation:

There are 8 classes of accuracy as per BIS.

16. In figure, Z1 = 200∠60° Ω, Z2 = 400∠ - 90° Ω, Z3 = 300∠0°. Then Z4 for bridge to be balanced is

A.

150∠30° Ω

B.

400∠ - 90° Ω

C.

300∠90° Ω

D.

600∠ - 150° Ω


Answer: Option D

Explanation:

.

17. In a ballistic galvanometer, a charge of 100 μC gives a first swing of 25°. The charge required to cause first swing of 50° is

A.

200 μC

B.

400 μC

C.

50 μC

D.

25 μC


Answer: Option B

Explanation:

swing is proportional to charge.

18. Two resistors R1 = 36 Ω ± 5% and R2 = 75 Ω ± 5% are connected in series. The total resistance is

A.

111 ± 0 Ω

B.

111 ± 2.778 Ω

C.

111 ± 5.55 Ω

D.

111 ± 7.23 Ω


Answer: Option C

Explanation:

Total maximum error ± (1.8 + 3.75) = ± 5.55 Ω.

19. Figure shows an RC potentiometer to measure ac voltage. It is desired that V0/Vishould be independent of frequency. The value of C should be

A.

10 μF

B.

11 μF

C.

0.1 μF

D.

0.09 μF


Answer: Option A

Explanation:

Since resistances are in the ratio of 10 : 1, capacitances should be in the ratio of 1 : 10 because XC ∝ 1/C.

20. In a strain measuring device using a strain gauge, the output quantity is

A.

voltage

B.

resistance

C.

impedance

D.

either (a) or (b)


Answer: Option A

Explanation:

The measurement is done using an unbalanced bridge.

21. 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 ωt, the Y-plate input is

A.

2 sin ωt

B.

2 sin (ωt + 45°)

C.

2 sin (ωt - 45°)

D.

22 sin ωt + 45°)


Answer: Option A

Explanation:

When signals to X and Y plates are in phase, the display is a straight line inclined at 45°.

22. The angle δ for a mica capacitor is about

A.

25°B.

15°

C.

5°D.

1°


Answer: Option D

Explanation:

Mica capacitor has very low loss and loss angle δ is very very small.

23. A digital voltmeter has a read out range from 0 to 999 counts. If the full scale reading is 9.999 V, the resolution is

A.

1 V

B.

0.01 V

C.

1 mV

D.

1 μV


Answer: Option C

Explanation:

Resolution is the smallest change in the quantity being measured which will cause an observable change in output. In this case it is 1 mV.

24. The coil of a moving coil meter has 100 turns, is 40 mm long and 30 mm wide. The control torque is 240 x 10-6 N-m on full scale. If B = 1 Wb/m2, range of meter is

A.

1 mA

B.

2 mA

C.

3 mA

D.

4 mA


Answer: Option B

Explanation:

NBAI = Controlling torque or

= 240 x 10-6 or I = 2 mA.

25. Consider the following statements: In a differential amplifier using JFET, the differential output offset is due to

1. mismatch between FET parameters2. difference in values of resistances used in circuit3. variation in supply voltage.

Of the statements, the correct statements are

A.

1 and 2

B.

1, 2, 3

C.

2, 3

D.

1, 3


Answer: Option A

Explanation:

Variation in supply voltage affects both amplifiers equally.

26. Magnetic flux density has the dimensions

A.

MI-1T-2 B.

M-1I-2T-2

C.

ML-3T-2 D.

MI-1T-3


Answer: Option A

Explanation:

Flux density = flux/area.

27. A meter with a resistance of 100 Ω 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

A. 490 Ω

B. 5000 Ω

C. 4900 Ω

D. 5100 Ω


Answer: Option C

Explanation:

.

28. In a resistance strain gauge, G = 2, stress = 1050 kg/cm2, R = 1000 Ω. The value of ΔR will be

A.

2 Ω

B.

3 Ω

C.

4 Ω

D.

1 Ω


Answer: Option D

Explanation:

.

29. The household energy meter is

A.

indicating instrument

B.

recording instrument

C.

integrating instrument

D.

none of the above


Answer: Option C

Explanation:

It integrates energy over a period of time.

30. 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

A.

1.39 V

B.

0.75 V

C.

13.9 V

D.

7.45 V


Answer: Option A

Explanation:

.

31. A full wave rectifier type meter is used to measure the wave shape shown in figure. The voltmeter is calibrated to read rms value of sine wave. The reading of voltmeter will be

A.

B.

C.

100 V

D.

111 V


Answer: Option D

Explanation:

Peak value of sine wave = 100 x 1.11 = 111 V.

32. A moving coil instrument has a resistance of 0.5 Ω and a full scale deflection of 0.1 A. To convert it into an ammeter of 0-10 A the shunt resistance should be

A.

0.004 Ω

B.

0.005 Ω

C.

0.05 Ω

D.

0.1 Ω


Answer: Option B

Explanation:

.

33. Potentiometer method of dc voltage measurement is more accurate than direct measurement using a voltmeter because

A.

it loads the circuit to maximum extent

B.

it loads the circuit moderately

C.

it does not load the circuit at all

D.

it uses centre zero galvanometer instead of Voltmeters


Answer: Option C

Explanation:

Since the circuit is not loaded, the accurate value of dc voltage is measured.

34. Assertion (A): A hot wire ammeter has a cramped scale.

Reason (R): The heat is proportional to square of current.

A.

Both A and R are true and R is correct explanation of A

B.

Both A and R are true but R is not correct explanation of A

C.

A is true R is false



Answer: Option A

Explanation:

Since heating ∝ I2, scale is cramped.

35. Which of the following is true about an impulse voltage?

A.

It is a unidirectional voltage

B.

Chopped impulse flashover does not occur

C.

Time taken to rise is equal to time taken to fall

D.

RMS value is always less than 50% of average value


Answer: Option A

Explanation:

Impulse is unidirectional (either positive or negative).

36. Which of the following are needed both for protection and metering?

A

.Wattmeters

B

.Instrument transformers

C

.Energy meters

D

.Power factor meters


Answer: Option B

Explanation:

Instrument transformers are used to measure high currents and voltages. They also feed the

relays for protection.

37. A digital frequency counter can be converted to DVM by addition of a suitable

A

.voltage controlled oscillator

B D/A converter

.

C

.power amplifier

D

.operational amplifier


Answer: Option B

Explanation:

D/A converter changes digital output to analog output.

38. A dynamometer wattmeter is connected in ac circuit. The reading will be

A.

V-A product

B.

average power

C.

peak power

D.

instantaneous power


Answer: Option B

Explanation:

Wattmeter measures average power over a cycle.

39. The speed transducer using a drag cup rotor has the main advantage of

A.

very high accuracy

B.

low energy requirement

C.

cheap construction

D.

all of the above


Answer: Option B

Explanation:

A drag cup rotor has low inertia. Therefore it requires little amount of energy.

40. A voltmeter using thermocouples measures

A

.rms value

B

.peak value

C

.average value

D

.peak to peak value


Answer: Option A

Explanation:

Since the thermocouple is based on heating effect, rms value is measured.

41. Which of the following measurements using a dc potentiometer do not require

standardisation of potentiometer?

A

.Measurement of unknown voltage

B

.Measurement of resistance

C

.Measurement of unknown current

D

.Calibration of voltmeter


Answer: Option B

Explanation:

Unknown resistance is compared with a standard resistance. Therefore standardisation of

potentiometer is not necessary.

42. Which of the following statement is correct for two wattmeters method of power

measurement in 3 phase circuit?

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.


Answer: Option D

Explanation:

When p.f. is zero, active power is zero and the two redaings are equal and opposite.

43. In a thermocouple temperature transducer, the output voltage is usually measured by

A

.high resistance ammeter

B

.high resistance voltmeter

C

.high resistance milli-voltmeter

D

.none of the above


Answer: Option C

Explanation:

The output voltage is very small. So we need a milli voltmeter.

44. A moving iron instrument gives correct reading when used at

A

.low frequencies

B

.high frequencies

C

.only one frequency

D

.all frequencies upto a certain value


Answer: Option C

Explanation:

If frequency changes reactance of coil changes and reading is affected.

45. Induction wattmeter can be used in

A

.ac circuit only

B

.dc circuit only

C

.both ac and dc circuit

D

.ac 3 phase only


Answer: Option A

Explanation:

Induction effect occurs with ac only. 46. A dynamometer wattmeter is connected in ac circuit. The measured power is

A

.rms power

B

.average power

C

.peak power

D

.instantaneous power


Answer: Option B

Explanation:

All wattmeters measure average power over a cycle.

47. Loss of charge method is suitable for medium resistances.

A

.True

B

.False


Answer: Option B

Explanation:

It is suitable for high resistances.

48. In two wattmeter method of 3 phase power measurement, when does one wattmeter read

negative

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


Answer: Option C

Explanation:

When p.f. is less than 0.5 (leading or lagging) one of the wattmeters reads negative.

49. It is required to measure angular position. Out of the transducers

1. Circular potentiometer2. LVDT3. E pick up4. Synchro

The proper devices are

A

.1, 2, 3, 4

B

.2 and 3

C

.1, 2, 4

D

.1 and 4


Answer: Option D

Explanation:

LVDT and E pickup are suitable for linear displacement.E

50. In figure the bridge is balanced when Z4 is

A

.120∠70°

B

.187.5∠ - 10°

C

.187.5∠ - 70°

D

.333.3∠ - 70°


Answer: Option C

Explanation:

.

section 1 measurement

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