(SEM-I) THEORY EXAMINATION 2019-20 PHYSICS

This is the complete B.Tech 1st Semester Engineering Physics (KAS101) question paper structured exactly as per the official 100-mark university exam pattern. It covers the full syllabus including Special Theory of Relativity, Electromagnetic Waves, Wave Optics, Quantum Mechanics, Lasers, Fiber Optics, Interference, Diffraction, and Photon Theory of Light.

This question paper is extremely useful for students preparing for semester exams, viva, and numerical practice, as it includes conceptual questions, derivations, numericals, and application-based physics problems.

SECTION A – Short Concept Questions (10 × 2 = 20 marks)

This section checks understanding of fundamental physics concepts:

Inertial vs non-inertial frames of reference

Why aircraft in steady flight is considered almost inertial

Massless particles, speed of light, and relation E = pc

Bohr’s quantization rule via de-Broglie matter waves

Dispersive power of transmission grating

Negligible modal dispersion in single-mode fibers

Wave impedance

Electromagnetic vs matter waves

Why independent sources do not interfere

Population inversion, laser basics, and energy relations

This part helps with fast revision of key definitions and reasoning concepts.

SECTION B – Descriptive Questions (Attempt Any 3 × 10 = 30 marks)

This section includes concept-based explanations and numerical problems:

Population inversion and comparison of He-Ne laser with Ruby laser

Time dilation problem involving round-trip space travel

Electric and magnetic field amplitudes using solar constant

De Broglie wavelength calculation

Resolving power of a diffraction grating and minimum resolvable wavelength

Relative population of laser states using Boltzmann distribution

These questions strengthen numerical ability and conceptual clarity.

SECTION C – Long Answer Questions (5 × 10 = 50 marks)

Students must attempt one part from each question. These include major derivations and advanced theory topics.

Q3 – Special Theory of Relativity

Postulates of relativity + derivation of Lorentz transformations + length contraction
OR

Einstein’s mass–energy relation and derivation of relativistic kinetic energy

Q4 – Electromagnetism

Maxwell’s equations in free space + displacement current + modification of Ampere’s law
OR

Poynting theorem and energy flow in EM fields

Q5 – Quantum Mechanics & Compton Effect

Schrödinger equation for a particle in 1-D box → eigenvalue & eigenfunction
OR

Compton effect and proof of photon nature of light

Q6 – Wave Optics

Formation of Newton’s rings + bright and dark ring conditions
OR

Fraunhofer diffraction at single slit + intensity of first subsidiary maximum ≈ 4.5%

Q7 – Fiber Optics & Lasers

Acceptance angle, acceptance cone, numerical aperture
OR

Ruby laser construction, working, and labeled diagram

These questions cover high-weightage derivations required to score full marks.