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

Total Questions: 100

31. Match the List-I with List-II.

Choose the correct answer from the options given below:

(a)(b)(c)(d)
A.IIIVIIII
B.IIIIIIIV
C.IVIIIIII
D.IIIIVIII
Correct Answer: D.
Solution:

(a) BCT is matched with III, as its symbol and operation indicate а special bipolar-controlled thyristor arrangement.
(b) RCT is matched with IV, being a reverse-conducting thyristor that has a built-in antiparallel diode.
(c) ETO is matched with II, an emitterturn-off-type thyristor allowing both turn-on and turn-off from its gate structure. A-66
(d) TRIAC is matched with I, as it can be triggered in both positive and negative half-cycles (Quadrants I and III).
Hence, the correspondence is: (a) → III, (b) → IV, (c) → II, (d) I.

32. Arrange the following with respect to their segregation coefficient in the increasing order.

(a) Al                        (b) As
(c) B                          (d) C
(e) P

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

Typical segregation coefficients K in silicon are smallest for aluminum (Al), then carbon (C), then arsenic (As), then phosphorus (P), and finally largest for boron (B). Numerically, one finds (Al < C < As < P < B).
Matching with the given labels,
(a) → AI, (d)→C, (b) → As, (e) → Р, (c) →B
Hence in ascending order: (a), (d), (b), (e), (c).

33. For a 4-bit counter arrange the following counters in increasing order of their valid counts.

(a) Ring counter           (b) Johnson counter
(c) Decade counter       (d) Ripple counter

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

For a 4-bit implementation, the number of distinct valid states is:
(a) Ring counter has 4 states (one "1" rotates through 4 flip-flops).
(b) Johnson (twisted-ring) counter has 8 states.
(c) Decade counter has 10 states.
(d) Ripple counter has all 16 possible states for 4 bits.
Hence in increasing order of valid counts:
(a)→(b) → (c) → (d).

34. For a series RLC circuit given below, arrange the driving point impedance |z| in descending order.

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

Because the circuit is series RLC, its impedance magnitude is least at (or near) resonance and grows larger as the frequencу moves away from that resonant point. Here, ω = 4000 Hz is close to the circuit's resonance, giving the smallest |Z|. Moving to lower or higher frequencies increases the net reactance in series and thus increases |Z|.

Comparing the four given frequencies, the largest magnitude of |Z| occurs at = 3200 Hz, followed by 4800 Hz, then 4400 Hz, and finally the smallest at 4000 Hz.

Hence, in descending order: (c) > (a) > (d) > (b).

35. Comparison of open loop and close loop control system

(a) Open loop systems are more stable in comparison to close loop system
(b) Open loop system are more reliable in comparison to close loop system
(c) Open loop systems are easy to build in comparison to close loop system
(d) Open loop system can be optimized while close loop cannot be optimized

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

Open-loop systems are often considered more stable in the sense that adding feedback may introduce complex poles that can lead to oscillations or instability if not designed carefully.
(c) They are indeed easier to build because they do not require feedback paths or sensors.
Options (b) and (d) are generally not true, so (a) and (c) are the correct statements.

36. For asynchronous sequential circuits:

(a) Memory elements are eîther unclocked FFs or time delay elements
(b) Change in input signal can affect memory elements upon activation of clock signal also
(c) Can operate faster than synchronous circuit because of absence of clock signal
(d) Easier to design

Correct Answer: A. (a) and (c) only
Solution:

(a) In asynchronous sequential circuits, the "memory" is typically in the form of unclocked latches or inherent delays rather than clock-triggered flip-flops.

(c) Because they do not wait for a clock edge, they can change states immediately upon input changes and often operate faster than a similar synchronous design.

Options (b) and (d) do not generally hold, so (a) and (c) are correct.

37. For the Instruction (in case of 8051) DIVAB

Which of the following statements is not correct?

Correct Answer: C. The carry flag is always set.
Solution:

For the 8051 instruction DIV A,В, the carry flag is cleared, not set. The other statements about overflow (division by zero) and where quotient/remainder go (in A and B, respectively) are correct. Thus "The carry flag is always set" is not correct.

38. The effective density of states in the conduction band N𝔠 (cm³) for Si & GaAs at 300K are:

(a) Si = 2.86 × 10¹⁹
(b) Si = 2.66 × 10¹⁹
(c) GaAs = 4.7 x 10¹⁷
(d) GaAs = 7.0 × 10¹⁸

Correct Answer: A. (a) and (c)
Solution:

Typical accepted values at 300 K:
(a) Silicon N𝔠 ≈ 2.8 × 10¹⁹ cm⁻³.
(c) GaAs N𝔠≈ 4.7 x 10¹⁷ cm⁻³.
Hence (a) and (c) are the correct pair.

39. For the 8051 microcontroller, during its operations in the serial data mode 2-(Multi Processor Mode) which of the following statements are correct:

Correct Answer: D. (a), (b) and (e) only
Solution:In 8051 serial mode 2 (also called 9-bit or multiprocessor mode),

Statements (c) and (d) do not apply as given, so (a), (b), (e) are correct.

40. For an infinitesimal electric dipole depicted in the figure below, the potential at point P and electric field components are given:

Correct Answer: B. (a) and (c) only
Solution:

For an infinitesimal dipole of moment p = ql oriented along the vertical axis, at a large distance r (with l² << r²):The standard dipole field formulas show that (b) and (d) are incorrect.