NTA UGC NET/JRF Exam, August -2024 (Electronic Science)

Total Questions: 100

71. The default offset register for code segment register (CS) in 8086 is:

Correct Answer: C. IP
Solution:

On the 8086 microprocessor, the default offset register for the code segment (CS) is the instruction pointer (IP), so the correct choice is C.

72. Using Mesh analysis find current I₁, for the circuit given below:

Correct Answer: C. 4 A

73. For SCR

(a) I²t rating of the SCR represents the capability to withstand the overload current for the specified time, where the current (I) is the rms value for the time interval t.
(b) The negative gate bias decreases the forward blocking capability and maximizes the false triggering possibility during high dv/dt operation
(c) Resistance at the gate increases the dv/dt capability and lowers the turn-off time
(d) The gate non trigger voltage is the maximum DC gate voltage that maybe applied between gate and anode for which the device can maintain its rated blocking voltage.
(e) The turn-off time becomes shorter due to introduction of Au Atoms in silicon, which serve as 'traps' for carriers, but it increases ON state loss.

Correct Answer: D. (c) and (e) only
Solution:

(c) Providing a suitable gate-to-cathode resistance in an SCR can help handle higher dv/dt stresses and also contribute to reducing the turn-off time by aiding in discharging the gate region.
(e) Gold (Au) diffusion in silicon creates recombination centers ("traps") that shorten the turn-off time, but at the cost of higher on-state losses.
Thus, only statements (c) and (e) are correct, given option D.

74. For the given circuit, the Thevenin's Equivalent circuit at a - b will be:

Correct Answer: D.

75. The accuracy of the series ohmmeter circuit consisting of a PMMC instrument with a series connected standard Resistor R₁ as shown in the given figure when the pointer is at 0.5 FSD is?

(The meter used has 1% accuracy. Assume Rₘ << R₁)

Correct Answer: C. 4%

76. If a coil draws 0.5 A from a 120 V, 60 Hz source at a 0.7 lagging power factor, then

(a) Coil resistance is 240
(b) Power factor angle is cos-¹ (0.7)
(c) Coil impendence is 168 + j171.4
(d) Power factor angle is 32.38°
(e) Coil induction is 0.455 Н

Correct Answer: B. (c) and (e) only

77. During the oxidation process, which of the following statements is not correct?

Correct Answer: C. For a growth of an oxide of thickness 'd', a layer of silicon with thickness of 0.88d is consumed.
Solution:

For thermal oxidation of silicon, the layer of silicon consumed is roughly 0.44d when the grown oxide thickness is d. Hence the statement claiming 0.88d is incorrect, making option (C) the wrong statement.

78. Arrange the following Antennas on the basis of increasing order of directivity

(a) Short dipole HPBW = 90°
(b) λ/4 monopole
(c) Isotropic (hypothetical)
(d) Hemispherical radiator
(e) λ/2 monopole

Correct Answer: C. (c), (a), (d), (b), (e)
Solution:

(least to most directional):
(c) Isotropic radiator
(a) Short dipole
(d) Hemispherical radiator
(b) λ/4 monopole
(e) λ/2 monopole
The correct increasing order directivity: (c),
(a), (d), (b), (e).

79. The Signal Flow Graph for the series RLC circuit given below is:

Correct Answer: C.

80. In data communication. MODEMS

(a) The word. MODEM is contraction derived from words Modulation and Demodulation
(b) MODEM is an interface between digital terminal equipments to analog communication facilities
(c) A MODEM transmitter is analog-todigital converter (ADC)
(d) The output of a MODEM is, a digital signal carrying analog information

Correct Answer: C. (a) and (b) only
Solution:

(a) A "modem" indeed derives from "modulator/demodulator."

(b) A modem is the interface between digital devices and analog transmission media.

(c) A modem transmitter is actually DAC-type (not ADC).

(d) A modem's output is an analog signal (not a digital signal).
Hence the correct statements are (a) and (b) only.