NTA UGC NET/JRF Exam, February-2023 (Electronic Science)

Total Questions: 100

81. Arrange following interrupts in order of polling (checking interrupt conditions) after every instructions.

(a) Serial Interrupt
(b) External 1 Interrupt
(c) Timer 1 Interrupt
(d) External 0 Interrupt
Choose the correct answer from the options given below:

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

The typical priority of polling interrupts in microcontrollers (such as the 8051) is as follows:

(d) External 0 Interrupt: Usually has the highest priority. (b) External 1 Interrupt: The next in the line after External 0.

(c) Timer 1 Interrupt: After checking external interrupts, the Timer interrupts are usually checked.

(a) Serial Interrupt: Often has the lowest priority among these.

Polling is a method where the CPU checks for interrupt conditions continuously. While it ensures that no interrupts are missed, it can be less efficient than hardware-driven interrupt handling.

82. Arrange the following in descending orders of energy gaps of semiconductor materials.

(a) Si
(b) Ge
(c) GaAs
(d) GaP
Choose the correct answer from the options given below:

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

The energy gap, often used as a measure of how much energy is required to excite an electron from its ground state to a conduction state, is different for various semiconductor materials. For the materials listed:
(d) GaP: ~2.26 eV
(c) GaAs: ~1.43 eV
(a) Si: ~1.12 eV
(b) Ge: ~0.66 eV
Energy gaps are fundamental in determining the electrical properties of semiconductors, and also affect the color of light emitted by LED devices made from these materials.

83. Arrange the following materials in increasing order of refractive Index

(a) Diamond
(b) Water
(c) Air
(d) Vacuum
Choose the correct answer from the options given below:

Correct Answer: E. (*)
Solution:

Either question or options is wrong.

84. Arrange the following in ascending order of their dielectric constants:

(a) Alcohol
(b) Nylon
(c) Water (dehydrated)
(d) Water (Fresh)
Choose the correct answer from the options given below:

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

The dielectric constant, also called relative permittivity, is a measure of a material's ability to store energy when placed in an electric field. In ascending order:
(c) Water (dehydrated): ~80
(b) Nylon: Ranges from ~3 to 4
(a) Alcohol (like Ethanol): ~24.5
(d) Water (Fresh): ~80 (But it's worth noting that pure water's dielectric constant can be even higher, while impurities in realworld samples can decrease it.)

Materials with higher dielectric constants can store more electrical energy, which is crucial for applications like capacitors.

85. Followings is the sequence of blocks in spectrum Analyser:

(a) Detector & Video Amplifier
(b) Fixed Frequency Active Filter
(c) Attenuator (Adjustable)
(d) Mixer & Tunable Detector
Choose the correct answer from the options given below:

Correct Answer: D. (c) (d) → (b) → (a)
Solution:

For a spectrum analyzer, which is used to measure the magnitude of input signals versus frequency:

(c) Attenuator (Adjustable): This block can reduce the amplitude of the input signal to protect the analyzer and can be adjusted depending on the signal's strength.

(d) Mixer & Tunable Detector: This mixes the input signal with a local oscillator to shift the signal's frequency.

(b) Fixed Frequency Active Filter: It can filter out unwanted frequencies, focusing on the desired frequency range.

(a) Detector & Video Amplifier: Detects and amplifies the filtered signal for display.

Spectrum analyzers are instrumental in studying the frequency spectrum of radio frequency, audio, and other signals.

86. Given below are two statements:

Statement I: Concentration of acceptor atoms in the region between isolation islands in а monolythic integrated circuit will be much higher then in a p-type substrate.
Statement II: The higher density is provided to prevent the depletion region.of the reverse biased isolation to substrate junction from extending into the p+ type material.
In the light of the above statements, choose the most appropriate answer from the options given below:

Correct Answer: A. Both Statement I and Statement II are correct
Solution:

Integrated circuits require precision engineering to work properly. In monolithic ICs, isolation is essential to prevent unintended electrical interaction between different components. The region between the isolation islands often has a p⁺ type material, which is essentially a p-type material but with a higher concentration of acceptor atoms.

Statement I correctly notes this heightened concentration compared to a regular p-type substrate. Statement II provides the rationale: the higher density is there to ensure the reverse-biased isolation to substrate junction's depletion region doesn't extend into the p⁺ material. If it did, it would jeopardize the isolation, leading to faulty operation.

87. Given below are two statements:

Statement I: In case a reverse biased photodiode is kept in a open light, the current flowing through the device corresponds to value of reverse saturation current.
Statement II: Photovoltaic emf. of semiconductor photodiode is that voltage at which the resultant current flowing the device becomes zero.
In the light of the above statement, choose the most appropriate answer from the options given below:

Correct Answer: D. Statement I is incorrect, but Statement II is correct
Solution:

For Statement I, when a reverse-biased photodiode is exposed to light, the photons hitting the diode generate electron-hole pairs, leading to a photocurrent. This photocurrent flows in the opposite direction of the reverse saturation current, and as a result, the net current flowing through the diode will be reduced, not equivalent to the reverse saturation current.

Thus, Statement I is incorrect. Statement II explains the photovoltaic effect seen in photodiodes. When a voltage equal in magnitude but opposite in polarity to the photovoltaic emf is applied, the net current through the device becomes zero. Hence, Statement II is accurate.

88. Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).

Assertion (A): Some instruction read the contents of an internal port latch instead of reading the status of an external pin.
Reason (R): We must not make a distinction between reading the status of the input pin and internal latch of the output port.
In the light of the above statements, choose the most appropriate answer from the options given below:

Correct Answer: C. (A) is correct, but (R) is not correct
Solution:

Assertion (A) indicates a behaviour observed in certain microcontrollers. Some instructions do read the status of an internal latch rather than the actual pin state. This can be useful for ensuring that the reading is stable and not subject to transient changes. Reason (R) is misleading.

In many cases, there's a distinct difference between reading the status of an input pin (which can change rapidly) and the more stable internal latch of an output port. Therefore, the assertion is correct, but the reason is not.

89. Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R):

Assertion (A): M-ary modulation scheme is preferable where bandwidth requirement is important.
Reason (R): In M-ary modulation scheme the BW (bandwidth) requirement is reduced by factors log M in comparison to BPSK system.
In the light of the above statements, choose the most appropriate answer from the options - given below:

Correct Answer: A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
Solution:

M-ary modulation schemes are indeed preferable in situations where bandwidth conservation is a priority, as indicated by Assertion (A). These modulation schemes, such as M-ary QAM or M-ary PSK, use symbols that represent log2(M) bits.

As a result, for each symbol transmitted, multiple bits of information are conveyed, leading to more efficient use of bandwidth. Reason (R) captures this essence by comparing it to BPSK (Binary Phase Shift Keying), which is a 2-level scheme.

For M-ary schemes, the bandwidth requirement is indeed reduced by factors of log2M compared to BPSK, making the reason correct and also the correct explanation for the assertion.

90. Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).

Assertion (A): Potentiometric type accelerometer have higher resolution than LVDT accelerometer.
Reason (R): The resistance offered to the motion is less in LVDT accelerometer than in potentiometric accelerometer.
In the light of the above statements, choose the most appropriate answer from the options given below:

Correct Answer: D. (A) is not correct, but (R) is correct
Solution:Potentiometric accelerometers and LVDT (Linear Variable Differential Transformer) accelerometers have distinct operating principles and advantages. Assertion (A) suggests that potentiometric accelerometers have higher resolution. However, this isn't intrinsically accurate.

The resolution of an accelerometer depends on various factors, including its design, noise characteristics, and the resolution of the associated electronics. It's not inherently true that potentiometric accelerometers always outperform LVDTs in terms of resolution.

On the other hand, Reason (R) suggests that LVDT accelerometers offer less resistance to motion than potentiometric accelerometers. LVDTs, being transformer-based devices, don't have the wiper contacts like potentiometric devices, which can introduce resistance. Thus, the resistance to motion, or friction, can indeed be less in LVDT accelerometers.