Electronics and Communication questions reward anyone who is comfortable moving between the time domain and the frequency domain. This set covers network theory, analog and digital circuits, signals and systems, control systems, communication systems, and electromagnetics. Numerical solutions keep the units visible at every step, since a dropped factor is the most common reason a correct method still produces a wrong option.
What is the primary function of a PN junction diode?
Answer: B
A PN junction diode exhibits rectification property, allowing current to flow easily in the forward direction (low resistance) and blocking it in the reverse direction (high resistance).
Q.2Easy
The barrier potential of a silicon PN junction at room temperature is approximately:
Answer: B
Silicon PN junctions have a built-in barrier potential of approximately 0.7 V at room temperature (25°C), while germanium junctions are around 0.3 V.
Q.3Easy
Which of the following is NOT a characteristic of a Zener diode?
Answer: C
Zener diodes have low forward resistance (like normal diodes in forward bias) but the unique property is controlled reverse breakdown at a specific voltage for regulation purposes.
Q.4Easy
In a BJT (Bipolar Junction Transistor), what are the three regions of operation?
Answer: B
BJT operates in three distinct regions: Active region (linear amplification with both junctions forward biased), Saturation (both junctions forward biased, acts as switch ON), and Cutoff (both junctions reverse biased, acts as switch OFF).
Q.5Easy
What is the relationship between collector current (Ic) and base current (Ib) in a BJT?
Answer: A
In BJT, the current gain (beta or hFE) is defined as the ratio of collector current to base current: β = Ic/Ib, so Ic = Ib × β. Beta typically ranges from 50 to 500 for most transistors.
Q.6Easy
An LED (Light Emitting Diode) emits light when:
Answer: B
LEDs emit light through electroluminescence when forward biased with sufficient current. The energy of emitted photons equals the bandgap energy of the semiconductor material.
Q.7Easy
Which of the following devices has the fastest switching speed?
Answer: B
MOSFETs have fastest switching due to voltage-controlled operation without minority carrier storage effects.
Q.8Easy
In an n-channel enhancement mode MOSFET, the threshold voltage (VT) is typically:
Answer: C
N-channel enhancement mode MOSFETs require positive gate voltage to create inversion layer for conduction.
Q.9Easy
Which of the following statements about Zener diodes is correct?
Answer: B
Zener diodes operate in reverse breakdown region maintaining nearly constant voltage for voltage regulation applications.
Q.10Easy
A light-emitting diode (LED) emits light when:
Answer: B
Forward bias injects minority carriers; their recombination releases energy as photons (electroluminescence) in direct bandgap semiconductors.
Q.11Easy
Which semiconductor material has the lowest bandgap at room temperature?
Answer: C
Germanium has Eg ≈ 0.66 eV at 300K, lowest among common semiconductors; causes high intrinsic carrier concentration and leakage current.
Q.12Easy
In a p-n junction diode, the depletion width increases when:
Answer: A
Reverse bias widens the depletion region by pulling majority carriers away from the junction, increasing the width of the space charge region.
Q.13Easy
Which of the following is true about intrinsic semiconductors at room temperature?
Answer: B
In intrinsic semiconductors, thermally generated electrons and holes are in equal numbers, making ni = pi at thermal equilibrium.
Q.14Easy
A BJT in saturation mode has:
Answer: A
In saturation, both BE and BC junctions are forward biased, resulting in VCE dropping to approximately 0.2-0.3V for silicon transistors.
Q.15Easy
The thermal voltage (VT) at 300K is approximately:
Answer: A
VT = kT/q where k=1.38×10⁻²³ J/K, T=300K, q=1.6×10⁻¹⁹C gives approximately 26 mV or 25 mV.
Q.16Easy
In an enhancement-mode NMOS transistor, the threshold voltage (VTh) is:
Answer: B
Enhancement-mode NMOS has positive VTh (typically 0.5-2V) because an inversion layer must be created at positive gate voltage.
Q.17Easy
In a p-n junction diode, the depletion width increases with:
Answer: A
Reverse bias voltage increases the electric field across the junction, expanding the depletion region width. The depletion width W is proportional to √V_r where V_r is reverse bias.
Q.18Easy
The diffusion potential (built-in potential) of a silicon p-n junction at room temperature is approximately:
Answer: B
For silicon at 300K, the built-in potential is typically 0.7 V, determined by V_bi = (kT/q)ln(N_a*N_d/n_i²). This value is fundamental for silicon device calculations.
Q.19Easy
A JFET is depletion-type because:
Answer: B
JFETs are called depletion-type devices because the channel is formed by a depletion region. The p-n junction (gate-channel) creates a depletion layer that widens with reverse bias, pinching off the channel.
Q.20Easy
In a silicon BJT at room temperature, for every 10°C increase in temperature, the leakage current I_CO approximately:
Answer: A
The reverse saturation current I_0 doubles for every 5-7°C rise in silicon at room temperature. Since I_CO ≈ I_0, it also doubles per 5-7°C, or roughly per 10°C it increases significantly (by factor of ≈1.5-2).
