Physics is where JEE ranks are usually won or lost, since a single conceptual slip changes the whole answer. Questions here span mechanics, rotational motion, thermodynamics, waves and oscillations, electrostatics, current electricity, magnetism, optics, and modern physics. Numerical problems carry full derivations so you can see which step you skipped, not just which option was right.
In a p-type semiconductor, the majority carriers are:
Answer: B
P-type semiconductors are doped with acceptor impurities which create holes as majority carriers. Electrons become minority carriers in p-type material.
Q.82Easy
When a p-n junction is reverse biased, the width of the depletion region:
Answer: C
Reverse bias strengthens the electric field across the junction, causing the depletion region to expand as more charge carriers are pulled away from the junction.
Q.83Medium
The diode equation for current through a p-n junction is I = I_s(e^(qV/kT) - 1). Here, I_s is:
Answer: A
I_s is the reverse saturation current, representing the leakage current when the junction is reverse biased. It depends on temperature and doping concentrations.
Q.84Medium
In a BJT operating in active mode, which of the following is correct?
Answer: B
In active mode, the BE junction is forward biased to inject carriers, while the BC junction is reverse biased to collect these carriers, ensuring transistor amplification.
Q.85Easy
The current gain β (beta) of a BJT is defined as:
Answer: A
The current gain β is the ratio of collector current to base current (I_c/I_b). For silicon transistors, typical β values range from 50 to 500.
Q.86Medium
In a MOSFET, the threshold voltage V_T increases with:
Answer: B
Higher substrate doping increases the surface potential needed to invert the channel, raising V_T. This is described by V_T = V_T0 + γ(√(2φ_f + V_SB) - √(2φ_f)).
Q.87Medium
In an n-channel MOSFET operating in saturation region, the drain current is approximately:
Answer: A
In saturation, the MOSFET acts as a voltage-controlled current source with I_D proportional to (V_GS - V_T)^2, independent of V_DS beyond saturation voltage.
Q.88Medium
The transconductance g_m of a MOSFET in saturation is:
Answer: A
Transconductance g_m = ∂I_D/∂V_GS measures how much the drain current changes with gate voltage, a key figure of merit in MOSFET amplifier design.
Q.89Medium
Which semiconductor material has the highest electron mobility at room temperature?
Answer: C
GaAs has electron mobility ~8500 cm²/Vs compared to Si (~1350 cm²/Vs), making it superior for high-frequency and high-speed applications.
Q.90Medium
In a light-emitting diode (LED), the color of emitted light depends primarily on:
Answer: B
The wavelength of emitted light λ = hc/E_g, where E_g is the bandgap. Different materials (GaAs, GaN, AlGaAs) emit different colors based on their bandgap energy.
Q.91Medium
A solar cell operates as a p-n junction under illumination. The maximum power output occurs at:
Answer: C
Maximum power point (MPP) occurs where P = V × I is maximum, typically at ~80% of V_oc and ~80% of I_sc, determined by the fill factor.
Q.92Hard
In a Zener diode, breakdown voltage is primarily determined by:
Answer: B
Higher doping concentrations create stronger electric fields at lower voltages, reducing Zener breakdown voltage. This allows designing Zeners with specific breakdown voltages (3.3V, 5.1V, etc.).
Q.93Hard
In a tunnel diode, the negative resistance region occurs due to:
Answer: B
At low forward bias, electrons tunnel through the narrow bandgap, creating peak current. As voltage increases, direct band-to-band current dominates, causing current to decrease with voltage (negative differential resistance).
Q.94Hard
The transconductance parameter μ_n × C_ox in a MOSFET depends on:
Answer: C
The process transconductance parameter k_n = μ_n × C_ox determines how efficiently the MOSFET converts gate voltage to drain current. Both μ_n and C_ox are independent device parameters.
Q.95Hard
In FinFET technology (used in modern 7nm and 5nm nodes), multiple gates are used to:
Answer: B
FinFETs employ multiple gates (typically 3 gates) wrapping around a thin silicon fin, providing superior electrostatic control of the channel, reducing short-channel effects and subthreshold swing.
Q.96Hard
In a CMOS inverter circuit, the propagation delay is minimized when:
Answer: B
Due to lower hole mobility in PMOS (~2-3 times lower than electron mobility in NMOS), the PMOS width must be 2-3 times larger to match switching speeds and minimize inverter delay.
Q.97Medium
In a p-n junction diode, the depletion width is primarily determined by which of the following factors?
Answer: A
The depletion width W = √(2εε₀(V_bi + V_R)/(eN_D N_A/(N_D + N_A))) depends on applied voltage, doping concentrations, and built-in potential. Both doping levels and reverse bias voltage are critical factors.
Q.98Medium
A photodiode is reverse-biased to operate in photoconductive mode. What is the primary advantage of this configuration over photovoltaic mode?
Answer: B
In photoconductive (reverse-bias) mode, the depletion region widens significantly, reducing junction capacitance and transit time, resulting in faster response (MHz to GHz range) and shot noise is suppressed due to the reverse field.
Q.99Hard
In a BJT transistor, the Early effect causes the collector current to increase slightly with increasing reverse bias on the collector-base junction. This is due to:
Answer: B
The Early effect occurs because increased reverse bias widens the depletion region, reducing the effective base width. This decreases recombination in the base and increases collector current. The Early voltage V_A is inversely proportional to base doping concentration.
Q.100Easy
A rectifier circuit uses a silicon diode with V_f = 0.7V and a germanium diode with V_f = 0.3V at the same forward current. Which statement is CORRECT regarding their applications in 2024 technology?
Answer: A
Silicon has dominated modern rectifiers because of significantly lower reverse saturation current (leakage ~nA at room temperature vs ~µA for Ge), better temperature stability, and superior thermal properties. The extra 0.4V drop is offset by reduced losses in high-power applications.
