Two identical conducting spheres carry charges +Q and -Q. When brought into contact, the charge on each sphere becomes:

The correct answer is A: 0 on both spheres. When identical conductors touch, charge redistributes equally. Total charge = Q + (-Q) = 0, so each gets 0 charge.

In a fiber optics cable, light undergoes total internal reflection. The minimum refractive index of the core material needed to guide light from air is:

The correct answer is C: 1.414. For total internal reflection at core-cladding boundary: n_core × sin(θc) = n_cladding × 1. For propagation at 45°, n_core ≥ √2 ≈ 1.414

A reversible cycle absorbs 100 J at 400 K and rejects heat at 300 K. What is the minimum heat rejected?

The correct answer is A: Q_c = 75 J. For reversible cycle: Q_h/T_h = Q_c/T_c. 100/400 = Q_c/300. Q_c = (100 × 300)/400 = 75 J

The binding energy per nucleon is maximum for:

The correct answer is A: Iron-56. Iron-56 has the maximum binding energy per nucleon (~8.8 MeV/nucleon), making it the most stable nucleus. This is a key concept in nuclear physics.

Two objects of mass 4 kg and 6 kg move towards each other with velocities 5 m/s and 3 m/s respectively. After perfectly inelastic collision, what is their common velocity?

The correct answer is A: 0.2 m/s. By momentum conservation: 4(5) - 6(3) = (4+6)v → 20 - 18 = 10v → v = 0.2 m/s

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JEE Physics
Semiconductors

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

23 Q 9 Topics Take Mock Test

Difficulty: All Easy Medium Hard 21–23 of 23

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.21 Easy Semiconductors

The bandgap of silicon at room temperature (300 K) is approximately:

A 0.7 eV

B 1.1 eV

C 1.5 eV

D 2.0 eV

Correct Answer: B. 1.1 eV

EXPLANATION

Silicon has a bandgap of approximately 1.1 eV at 300 K. This is a standard value used in semiconductor physics and device design.

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Q.22 Easy Semiconductors

At absolute zero temperature, the number of free electrons in an intrinsic semiconductor is:

A Maximum

B Zero

C Equal to holes

D Approximately equal to doping concentration

Correct Answer: B. Zero

EXPLANATION

At T = 0 K, all electrons remain in the valence band. No thermal energy is available to excite electrons to the conduction band, so free electrons are zero.

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Q.23 Easy Semiconductors

Which of the following is a direct bandgap semiconductor?

A Gallium Arsenide (GaAs)

B Silicon (Si)

C Germanium (Ge)

D Carbon (C)

Correct Answer: A. Gallium Arsenide (GaAs)

EXPLANATION

GaAs is a direct bandgap semiconductor where the minimum energy gap occurs at the same k-value, making it suitable for light emission. Si and Ge are indirect bandgap semiconductors.

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JEE Physics
Semiconductors