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

Total Questions: 100

81. Which of the following statements are correct about the basic transistor amplifier configuration?

(a) The voltage gain of CB amplifier is higher than the voltage gain of CC amplifier
(b) The CB amplifier has low input impedance and a low current gain
(c) The CC amplifier has high input impedance and a low current gain
(d) The CC amplifier has low output impedance and a high current gain
(e) The CC amplifier has low input impedance and a low current gain

Correct Answer: A. (a), (b) and (d) only
Solution:(a) A common-base (CB) amplifier can have substantial voltage gain, whereas common-collector (CC) is near unity voltage gain.
(b) CB has low input impedance and low current gain (α< 1).
(d) CC (emitter follower) has low output impedance and high current gain.

82. Which of the following statements are correct when effective mass of an electron is taken into consideration:

(a) The electron effective mass is independent of the semiconductor properties.
(b) Electrons near top of the V.B. have negative effective mass
(c) The C.B. electron effective mass has a strong dependence on the value of bandgap
(d) The effective mass decreases as the bandgap increases.

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

(b) Near the top of the valence band, the energy-band curvature is inverted, giving electrons a negative effective mass.
(c) The conduction-band effective mass indeed depends strongly on the semiconductor's band structure (including gap).
(a) and (d) are not generally true.

83. The Doppler frequency seen by a stationary radar with a (CW) transmit frequency of 5 GHz and target radial velocity of 100 km/hr is:

Correct Answer: D. 927 Hz
Solution:For a stationary radar of frequency ƒ₀ = 5 GHz and a target speed of 100 km/h (≈ 27.78 m/s), the Doppler shift in reflection is

84. The bridge rectifier circuit as shown below has the following parameters: Vᵢ = 30 V, Rʟ = 300 and the diodes have Vꜰ = 0.7 V. The peak output voltage and peak output current value is:

Correct Answer: C. 41 V, 137 mA

85. Which of the following statements are correct?

(a) Light Dependent Resistors (LDRS) are based on Photo conductive Effect.
(b) In LDRs, resistance increases from its dark resistance value with increase in light intensity.
(c) LDRs are slow responding to changes in light intensity.
(d) Photodiodes can be operated only in the photoconductive region.
(e) Photodiodes have a faster switching time than Photo-transistors.

Correct Answer: D. (a), (c) and (e) only

86. In case of Avalanche Photo Detector (APD)

(a) APD is more sensitive than PIN photo diode
(b) APD is a PIN structure
(c) A high electric field intensity is required in APD
(d) There is less noise generation in APD as compared to PIN photo diode

Correct Answer: D. (a) and (c) only
Solution:(a) An APD (avalanche photodiode) is more sensitive than a simple PIN diode due to avalanche multiplication.

(c) It requires a high internal electricfield region for avalanche action. (b) can be contentious because an APD has a more specialized structure than a basic "PIN," and (d) is incorrect (an APD typically has more noise than a PIN diode).

The correct statements are (a) and (c).

87. Match the List-I with List-II. Breakdown Electric fields in the following materials:

List-I (Name of the material)List-II (Breakdown Electric field (V/cm))
(a) GaAsI.  10⁵
(b) SiCII.  4 ×10⁵
(c) Si₃N₄III. 2.3 × 10⁶
(d) GeIV. 10⁷

Choose the correct answer from the options given below:

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

(Typical breakdown fields in V/cm):
(a) GaAs → 4 × 105
(b) SiC→ 2.3 × 106
(c) Si,N→ 107
(d) Ge→ 105
So, the correct answers are: (a) → II, (b) → III, (c) → IV, (d) → І.

88. For an electrodynamic wattmeter, which of the following statements are correct?

(a) It measures average power over a time period.
(b) The moving coil is called as the voltage coil.
(c) The field coil are connected in parallel with the load.
(d) The field coils are called as the voltage coils.
(e) The moving coil is connected in parallel with the load.

Correct Answer: B. (a), (b) and (e) only
Solution:

(a) An electrodynamic wattmeter measures the average power.
(b) The moving coil is the "voltage coil."
(e) The moving (voltage) coil is connected in parallel with the load.
Meanwhile, the fixed (field) coils are in series with the load (the "current coil"). The correct statements are (a), (b), (e).

89. The magnetic field at the centre of the loop 1.e. H(0,0,0) is given by:

Correct Answer: B.

90. The 8-bit stack pointer (SP) register is used by the 8051 to hold an internal RAМ address that is called the top of the stack. When the 8051 is reset, what is the value of SP?

Correct Answer: В. 07 H