Entrevistas y análisis de contenidos/discurso

2. (a) The permanent magnet moving coil measures the DC value only. The torque will be reversed if the current is reversed. If the instrument is connected to AC, the deflection responds to the mean torque which is zero. Hence, voltmeter reads 2 V.

3. (d) Given, =w xy z Taking log, we get,

log w = log x + log y + log z

By considering only positive error, differentiating with respect to w, we get, for maximum uncertainly

é ù 100

4. (b) Reading of Energy Meter = 2.3 Units (kWH)

3 V2 230 230

\ Power dissipated in kW =

6. (b) At balance condition,

~

8. (c) PMMC instrument leads only DC value and since, it is centre zero type so, it will give –8 value. RMS meter will read rms value of the current

So, RMS =

Moving iron also reads rms value, so its reading will also be 10 A, hence ultimately it will be (–8, 10, 10).

9. (c) p-p division of upper trace voltage = 2 and value of p-p voltage = 5V

Voltage 2.5 divisions

\ =

Now it will same for unknown voltage, p-p division of unknown voltage = 3 So p-p voltage = 3 × 2.5 = 7.5 voltage Frequency of upper trace = 1 kHz.

\ Time Period = 1₃ ³ 10 1 ms 10

= - = and division on x-axis = 4 Thus, ^{Time 1 ms}

Division = 4

and division of Lower trace voltage on x-axis = 8 Thus, Time 1 ms

Division = 4

Period of unknown signal, Time Division

æ ö

ç ÷

è ø × 8 = 2 ms

10. (a) From waveform it is clear that for half of time period the power is of opposite sign of equal amplitude to another half of the time period. The total power in one period is zero. Hence, the reading of wattmeter is zero.

Equating real and Imaginary terms, we get, L₁ =

Quality factor, ¹

1 4 4

= Number of times tangent touches top or bottom Number of times tangent touches either side

2

Assume V_ab as reference phasor, we have V_ab = VÐ0°

V_bc = 400 Ж120°

V_ca = 400 Ж240°

Current through current coil,

2

and, voltage across pressure coil, V_pc = V_bc = 400 Ж120° 17. (d) For triangular wave,

Average value = ^V₃^m

18. (d) The relative error of product or division of different quantities is equal to the sum of relative errors of individual quantities.

19. (b) Pressure coil of a dynamometer type wattmeter is made to have very high resistance which includes small unavoidable inductance.

20. (b) In X-Y mode, if figure shows ellipse that indicates the amplitude is not equal but it changes to circle means amplitudes are equal. The inference can be made from the amplitudes of the signal are very close but not equal.

21. (a)

Equating real and imaginary parts,

3

Let 5A through ammeter A₁. So, remaining current through R_sh, I = 25 – 5 = 20 A

\ 20 × R_sh = 0.2 × 5 Þ R_sh = 1

20=0.05W

23. (c) The fixed coil or field coil is connected in series with the load and so carries the current in the circuit. The fixed coil therefore forms the current coil. The moving coil is connected across the voltage and therefore carries a current proportional to voltage.

24. (c) Number of full digits = 4 Maximum count with 1

42 digits display = 19999 Full-scale reading = 200 V

1 Count = ^200V 19999

Then, error corresponding to 10 counts

= ^{10 200} 19999

´ = 0.1 V

and, error corresponding to 0.2% of reading

= ^{0.2 100}

´100 = 0.2 V

Hence total error, E = E₁ + E₂ = 0.3V

% percentage error = ^E 100%

100´ = ±0.3%

25. (b) The compensating coil is made nearly identical with the current coil and is also coincident with the current coil and opposes the field produce by current coil.

The additional conductor is an internal connections, corresponding to the lead from P to Q of Fig. which carries the voltage-coil current in a reverse direction through the winding.

Thus any extra torque due to the voltage-coil current in the current coil itself is neutralized by the torque due to the voltage-coil current in the additional winding.

26. (c) Oscilloscope with two vertical inputs, referred to as dual trace oscilloscope. Using a single-beam CRT, they multiplex the inputs, usually switching between them fast enough to display two traces apparently at once.

Switching channels can be asynchronous, i.e., free running with trace blanking while switching or after each horizontal sweep is complete. Asynchronous switching is usually designated chopped while sweep-synchronised is designated att [esnate].

27. (c) The circuit shown in the figure is the Maxwell's inductance-capacitance bridge. In this bridge, an inductance is measured by comparison with a standard capacitance. This bridge is limited to measurement of low Q coil.

28. (d) Let resistance of voltmeter be RkW.

–

29. (c) Average power,

<P> =

All other terms are zero.

cos(2 ).

31. (a) PMMC type of instrument measure average value

= Area of graph

32. (a)

1 kW

100 kW

D Voltmeter

+ –

During the half cycle, the diode is forward biased (anode is connected to positive, Cathode is connected to negative).

The voltage across forward biased ideal diode is zero.

During –ve half cycle the diode is reversed biased.

Cathode is connected to negative, cathode is connected to positive).

The average voltage across the voltmeter will be 2

3 3

100 10 1

14.14 4.46V

100 10 1 10 2

´ ´ ´ =

´ + ´

Input Voltage

10 ms

20 ms 14.14

wt, t

10 ms 20 ms t 14.14

Voltage across the voltmeter

33. (d) V₂ > V₁ and phase difference is 180 and hence MI/

voltmeter will read V = V₂ – V₁

34. (c) Maximum permissible voltage = (300 + 300) × 20 × 10^–3

= 12 V

R₁ R₂

R₃ R_s

V₀ Q

d +

– b

when R_s is increased by 1% new value of R 'e =303W

0 0 1 mn

v =v -v =v -v

= ^6-300₆₀₃^´12=

(

^{6 5.97 v-}

)

= 0.03 v = 30 mv 35. (b) horizontal axis

36. 140 to 142 37. 3.0 to 3.4 38. 17.34 W

Total power dissipated in the circuit is 1kW.

P = 1kW 1000 = I².1+ I².R.

1000 = (2)² . 1 + (10)² . R.

Þ R=9.96W

|Z| = ^{V 200 20} 1 Þ 10 =

|Z| = R²+X_L² Þ X²_L = (Z)²-R² Þ X²_L = (20)² – (9.96)² Þ XL =17.34W 39. 10.157

X and Y ammeters are connected in parallel Shunt Registration of X and Y meters:

15A

R_shx

I_mx= 150mA = 250mA R_shy 1.2W 1.5W

I_my

R_shx = ^1.2₃ 15 10

150 1 æ ´ - ö

ç ÷

è ø

R_shx = 0.01212W R_shy = ^1.5₃ 15 10

250 1 æ ´ - ö

ç ÷

è ø

R_shy = 0.02542W

Current through X ammeter is

= 0.02542 (0.1212 0.2542)´15

+

= 10.157 amperes

40. 2

Power at full scale reading = 150 Current range used = 10A Voltage range used = 150V Power factor = 0.2

Multiplying factor =

Current range used voltage range p.f.

Power at full scale reading

´ ´

1. (c) Induction principle is more generally used for Watt-hour meters than for ammeters and voltmeters owing to their comparatively high cost, and inaccuracy of induction instruments of the latter types.

2. (b)

6. (a) Average current = 117.02 117.08 117.11 117.03 4

9. (d) Refer potentiometric type digital voltmeter 10. (b)

11. (b) LVDT & strain gauge measure linear displacement.

12. (d) T_d = qC , T_d =KI²

15. (c) Work done by the electric field = eV Kinetic energy = ¹mv²

In document MANUAL PARA REALIZAR INVESTIGACIONES SOBRE TELEVISIÓN (página 72-76)