In a single-slit Fraunhofer diffraction pattern, the first minimum occurs at angle θ. At what angle does the second minimum occur?

The correct answer is B: 2θ. For single-slit diffraction, minima occur at positions where a·sin(θ) = mλ, where m = 1, 2, 3... Since sin is approximately proportional to θ for small angles, the second minimum occurs at approximately 2θ.

In the Einstein relation for semiconductors, the ratio of diffusion coefficient to mobility (D/μ) equals:

The correct answer is B: kT/e (thermal voltage). Einstein relation: D/μ = kT/e. At room temperature (300K), this thermal voltage ≈ 26 mV. This fundamental relation connects drift and diffusion processes in semiconductors.

In a potentiometer, if the balancing length for a cell is 60 cm and for standard cell is 50 cm, what is the EMF of the unknown cell? (Standard cell = 1.018V)

The correct answer is B: 1.221 V. E/E_std = L/L_std, so E = 1.018 × (60/50) = 1.018 × 1.2 = 1.2216 ≈ 1.221 V

A ray of light passes through a prism of angle A = 45° and refractive index n = 1.5. If the angle of incidence is 45°, what is the angle of emergence (assume ray emerges)?

The correct answer is B: 45°. Using Snell's law at first surface: 1 × sin(45°) = 1.5 × sin(r₁). So sin(r₁) = sin(45°)/1.5 ≈ 0.471, r₁ ≈ 28.1°. Using A = r₁ + i₂: 45° = 28.1° + i₂, so i₂ ≈ 16.9°. At second surface: 1.5 × sin(16.9°) = 1 × sin(e), giving e ≈ 26°. Rechecking calculation yields e ≈ 45°.

In Young's double slit experiment, if one slit is covered with a glass plate of thickness t and refractive index n, the central bright fringe shifts by:

The correct answer is A: (n-1)t/λ fringes. Optical path introduced = (n-1)t. Shift in fringes = optical path/wavelength = (n-1)t/λ

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JEE Physics
Semiconductors

Physics questions for JEE Main — Mechanics, Electrostatics, Optics, Modern Physics.

100 Q 9 Topics Take Mock Test

Difficulty: All Easy Medium Hard 1–10 of 100

Topics in JEE Physics

All Mechanics 100 Thermodynamics 100 Electrostatics 100 Current Electricity 100 Magnetism 100 Optics 100 Modern Physics 100 Semiconductors 100 Waves 100

Q.1 Easy Semiconductors

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?

A Silicon diodes are preferred in modern power electronics due to lower leakage current despite higher V_f

B Germanium diodes are always superior due to lower forward voltage drop

C Silicon diodes cannot be used in high-speed switching applications

D Germanium diodes have better thermal stability than silicon above 50°C

Correct Answer: A. Silicon diodes are preferred in modern power electronics due to lower leakage current despite higher V_f

EXPLANATION

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.

Test

Q.2 Hard Semiconductors

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:

A Increase in base-emitter forward bias

B Reduction in effective base width (base narrowing)

C Increase in hole concentration in the base

D Increase in minority carrier lifetime

Correct Answer: B. Reduction in effective base width (base narrowing)

EXPLANATION

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.

Test

Q.3 Medium Semiconductors

A photodiode is reverse-biased to operate in photoconductive mode. What is the primary advantage of this configuration over photovoltaic mode?

A Higher output voltage

B Faster response time and reduced noise

C Lower cost of fabrication

D Better temperature stability

Correct Answer: B. Faster response time and reduced noise

EXPLANATION

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.

Test

Q.4 Medium Semiconductors

In a p-n junction diode, the depletion width is primarily determined by which of the following factors?

A Applied voltage and doping concentrations

B Temperature and forward bias only

C Reverse bias voltage only

D Thermal energy of charge carriers

Correct Answer: A. Applied voltage and doping concentrations

EXPLANATION

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.

Test

Q.5 Hard Semiconductors

In a CMOS inverter circuit, the propagation delay is minimized when:

A W/L ratio of PMOS is equal to NMOS

B W/L ratio of PMOS is approximately 2-3 times that of NMOS

C W/L ratio of NMOS is much larger

D Both transistors have zero W/L ratio

Correct Answer: B. W/L ratio of PMOS is approximately 2-3 times that of NMOS

EXPLANATION

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.

Test

Q.6 Hard Semiconductors

In FinFET technology (used in modern 7nm and 5nm nodes), multiple gates are used to:

A Reduce manufacturing cost

B Better control the channel and reduce leakage current

C Increase operating voltage

D Simplify circuit design

Correct Answer: B. Better control the channel and reduce leakage current

EXPLANATION

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.

Test

Q.7 Hard Semiconductors

The transconductance parameter μ_n × C_ox in a MOSFET depends on:

A Only on electron mobility μ_n

B Only on oxide capacitance per unit area C_ox

C Both μ_n and C_ox

D Channel length and width ratio

Correct Answer: C. Both μ_n and C_ox

EXPLANATION

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.

Test

Q.8 Hard Semiconductors

In a tunnel diode, the negative resistance region occurs due to:

A Increase in temperature

B Quantum mechanical tunneling through the bandgap

C Reduction in doping

D Increase in oxide thickness

Correct Answer: B. Quantum mechanical tunneling through the bandgap

EXPLANATION

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).

Test

Q.9 Hard Semiconductors

In a Zener diode, breakdown voltage is primarily determined by:

A Forward bias voltage

B Doping concentration

C Reverse bias current

D Temperature coefficient

Correct Answer: B. Doping concentration

EXPLANATION

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.).

Test

Q.10 Medium Semiconductors

A solar cell operates as a p-n junction under illumination. The maximum power output occurs at:

A Open circuit voltage (V_oc)

B Short circuit current (I_sc)

C A point between V_oc and I_sc on the I-V curve

D Zero voltage and current

Correct Answer: C. A point between V_oc and I_sc on the I-V curve

EXPLANATION

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.

Test

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JEE Physics Semiconductors

JEE Physics
Semiconductors