CFTRI M.Sc. (Food Technology) Physics Flashcards

24 sample cards from the Physics deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. Define reflection of light and state the law of reflection.

   Reflection is the bouncing back of light when it strikes a surface. Law of reflection: the angle of incidence equals the angle of reflection, and the incident ray, reflected ray, and normal all lie in the same plane.

2. Define refraction of light.

   Refraction is the bending of light as it passes from one transparent medium to another due to a change in its speed. Light bends toward the normal entering a denser medium and away from the normal entering a rarer medium.

3. State Snell's law of refraction.

   n₁ sin θ₁ = n₂ sin θ₂, where n₁ and n₂ are the refractive indices of the two media and θ₁, θ₂ are the angles of incidence and refraction respectively.

4. Define refractive index of a medium.

   The refractive index (n) is the ratio of the speed of light in vacuum to its speed in the medium: n = c/v. It indicates how much light slows down and bends in that medium.

5. What is total internal reflection and what is required for it?

   Total internal reflection occurs when light traveling in a denser medium strikes the boundary with a rarer medium at an angle greater than the critical angle; all light is reflected back. It requires light to travel from a denser to a rarer medium.

6. Define the critical angle and give its formula.

   The critical angle is the angle of incidence in the denser medium for which the angle of refraction is 90°. Formula: sin θ_c = n₂/n₁ (rarer over denser), or sin θ_c = 1/n for a medium-to-vacuum interface.

7. Define diffraction of light.

   Diffraction is the bending and spreading of light waves around the edges of an obstacle or through a narrow aperture, becoming significant when the size of the obstacle/slit is comparable to the wavelength of light.

8. Define interference of light.

   Interference is the superposition of two or more coherent light waves, producing regions of increased brightness (constructive interference) and darkness (destructive interference).

9. Distinguish between constructive and destructive interference.

   Constructive interference occurs when waves are in phase (path difference = nλ), producing maximum amplitude/brightness. Destructive interference occurs when waves are out of phase (path difference = (n+½)λ), producing minimum/zero amplitude.

10. Define polarization of light.

    Polarization is the restriction of the vibrations of a light (transverse) wave to a single plane. It demonstrates that light is a transverse wave; longitudinal waves like sound cannot be polarized.

11. State the lens (and mirror) thin-lens formula relating focal length, object and image distances.

    1/f = 1/v − 1/u (lens convention), relating focal length f, image distance v, and object distance u. For mirrors the formula is 1/f = 1/v + 1/u.

12. Define magnifying power (magnification) of a lens.

    Magnification is the ratio of image size to object size, m = h_image/h_object = v/u. A value greater than 1 means the image is enlarged; a negative sign indicates an inverted image.

13. What is dispersion of light?

    Dispersion is the splitting of white light into its constituent colors (spectrum) when it passes through a prism, because the refractive index—and hence the bending—differs for each wavelength (violet bends most, red least).

14. Differentiate between a real and a virtual image.

    A real image is formed where light rays actually converge; it can be projected on a screen and is usually inverted. A virtual image is formed where rays only appear to diverge from; it cannot be projected and is usually upright.

15. What experimental observation does quantum physics introduce about energy?

    Energy is quantized—it is emitted, absorbed, and exists in discrete packets (quanta) rather than continuously. This was first proposed by Max Planck to explain black-body radiation.

16. State Planck's quantum hypothesis and the energy formula.

    Energy is emitted or absorbed in discrete quanta proportional to frequency: E = hν, where h is Planck's constant (6.626 × 10⁻³⁴ J·s) and ν is the frequency of radiation.

17. What is a photon?

    A photon is a quantum (discrete packet) of electromagnetic energy with energy E = hν. It has zero rest mass, travels at the speed of light, and exhibits both wave and particle properties.

18. Explain the photoelectric effect.

    The photoelectric effect is the emission of electrons from a metal surface when light of sufficient frequency falls on it. It demonstrated the particle nature of light; Einstein's equation: hν = φ + KE_max, where φ is the work function.

19. Define the work function in the photoelectric effect.

    The work function (φ) is the minimum energy required to remove (eject) an electron from the surface of a metal. Below the corresponding threshold frequency, no electrons are emitted regardless of light intensity.

20. State de Broglie's hypothesis and the wavelength formula.

    All moving matter has an associated wave; the de Broglie wavelength is λ = h/p = h/(mv), where h is Planck's constant, p is momentum, m is mass, and v is velocity. This introduced wave–particle duality for matter.

21. State Heisenberg's uncertainty principle.

    It is impossible to simultaneously determine both the exact position and exact momentum of a particle. Mathematically: Δx · Δp ≥ h/4π, where Δx is uncertainty in position and Δp uncertainty in momentum.

22. What is wave–particle duality?

    Wave–particle duality is the concept that matter and radiation exhibit both wave-like and particle-like properties depending on the experiment. For example, light shows interference (wave) and the photoelectric effect (particle).

23. What is the significance of the wave function (ψ) in quantum mechanics?

    The wave function ψ contains all the information about a quantum system. Its squared magnitude |ψ|² gives the probability density of finding the particle at a given position (Born interpretation).

24. What did the Bohr model contribute to quantum physics regarding electron orbits?

    Bohr proposed that electrons revolve in fixed, quantized orbits (stationary states) without radiating energy, and that energy is emitted or absorbed only when an electron jumps between orbits, with ΔE = hν. Angular momentum is quantized as mvr = nh/2π.

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