In a nuclear reactor, heavy water is used as MCQ with Answer and Explanation

Explanation:
Rocket propulsion: expelled gases backwards impart forward momentum to rocket. Total momentum of rocket + exhaust gases remains conserved. No external force, so momentum conservation applies. Jet engines also work on similar principle.

Explanation:
Motor converts electrical to mechanical energy using force on a current-carrying conductor in magnetic field (F = BIL). Electromagnetic induction is for generator. Motor principle: A current-carrying coil experiences torque in magnetic field.

Explanation:
Diffraction causes light waves to spread when passing through apertures or around obstacles, creating Airy patterns instead of point images. This fundamental wave effect limits the minimum resolvable detail (Rayleigh criterion: θ_min ≈ 1.22λ/D). Options B, C, D are practical limitations but not the fundamental diffraction limit. Memory tip: 'Diffraction limit: smaller λ or larger aperture ⇒ better resolution'. This wave optics concept is frequently tested in competitive exams. Always distinguish fundamental limits (diffraction) from technical limitations (aberrations, turbulence) in instrument performance.