Free Optics MCQs with Answers

• A. 5I and I
• B. 5I and 3I
• C. 9I and I
• D. 9I and 3I

Explanation: Amplitudes ∝ √I. Max intensity Imax = (√I + √4I)² = (1+2)² I = 9I. Min intensity Imin = (1−2)² I = 1 I. Thus extremes are 9I and I.

• A. The intensity of light gradually decreases to zero and remains at zero
• B. The intensity of light gradually increases to a maximum and remains at maximum
• C. There is no change in intensity
• D. The intensity of light is twice maximum and twice zero

Explanation: When plane polarized light passes through a polaroid, and the polaroid is rotated, the intensity of light gradually decreases to zero and…

• A. Joule
• B. Hertz
• C. Diopter
• D. Meter

Explanation: Lens power (P) = 1/f (in meters). The unit of power of a lens is diopter (D).

• A. Quantum nature of light
• B. Complex nature of light
• C. Wave nature of light
• D. Transverse nature of light

Explanation: Interference and diffraction arise from the superposition of wavefronts and are classical demonstrations of light's wave behaviour…

• A. Zero
• B. 3 × 10⁵ km sec⁻¹
• C. 3 × 10⁸ km sec⁻¹
• D. Infinite

Explanation: The speed of light in vacuum is c ≈ 3.00×10⁸ m/s, which equals 3.00×10⁵ km/s. Option B expresses that value in km·s⁻¹.

• A. Vibrations take place in all directions
• B. Vibrations take place in two perpendicular directions
• C. No vibrations at all
• D. Vibrations take place in one plane perpendicular to the direction of propagation of light

Explanation: Plane-polarized light has its electric field oscillating in a single plane perpendicular to propagation; the field components in other…

• A. The central spot is bright
• B. The central spot is dark
• C. Both of the above
• D. None of these

Explanation: At the point of contact, the reflected rays suffer a phase inversion, causing destructive interference in reflected light; hence, the…

• A. Doubled
• B. Four times
• C. Half
• D. The same

Explanation: Fringe width β = λ D / d. If D → 2D and d → 2d, the ratio D/d remains unchanged, so β stays the same.

• A. Dispersion
• B. Refraction
• C. Reflection
• D. Interference

Explanation: Multiple reflections from the film's two surfaces produce phase-shifted waves that interfere constructively or destructively at different…

• A. Scattering in red is less than in yellow
• B. Scattering in yellow is less than that of red
• C. Red light is longer in wavelength than yellow
• D. None of these

Explanation: Red light has the longest wavelength among visible colours, which means it scatters the least when travelling through air particles.

• A. Inverted
• B. Real
• C. Erect
• D. Magnified

Explanation: Virtual images cannot be projected on a screen and are always upright (erect). Plane mirrors and convex mirrors form virtual, erect images.

• A. A spherical wave front
• B. A plane wave front
• C. A cylindrical wave front
• D. An elliptical wave front

Explanation: A point source radiates uniformly in all directions in a homogeneous medium, so at any instant the disturbance occupies a spherical…

• A. From denser to rarer medium
• B. From rarer to denser medium
• C. From vacuum to glass
• D. From air to glass

Explanation: Total internal reflection occurs only when light moves from a denser medium (like water or glass) to a rarer one (like air) and the angle…

• A. Newton
• B. Fresnel
• C. Maxwell
• D. Huygens

Explanation: Huygens proposed the wave theory of light (Huygens' principle), explaining propagation and wavefront construction; later, Fresnel and…

• A. The wavelength of light used
• B. The distance of screen from the coherent sources
• C. Separation between the sources
• D. All of the above

Explanation: Fringe spacing β = λ D / d depends directly on wavelength λ and screen distance D and inversely on slit separation d; thus all listed…

• A. Magnetic field
• B. Electric field
• C. Electric and magnetic field
• D. Gravitational field

Explanation: Electromagnetic waves are time‑varying electric and magnetic fields oscillating orthogonally and propagating through a vacuum without…

• A. sin θ= dm λ
• B. 2d sin θ = mλ
• C. d sin θ = mλ
• D. d sin θ = 2mλ

Explanation: Grating maxima occur when the path difference between adjacent slits is mλ: d sinθ = mλ (m integer), giving constructive interference at…

• A. Particle nature only
• B. Wave nature only
• C. Dual nature
• D. Electromagnetic wave nature

Explanation: Quantum theory demonstrates light exhibits both wave-like (interference, diffraction) and particle-like (photons, photoelectric effect)…

• A. Time period
• B. Frequency
• C. Wavelength
• D. None of these

Explanation: In vacuum c is a universal constant independent of the light's frequency, wavelength or period.

• A. Wavelength only
• B. Frequency only
• C. Velocity only
• D. Both velocity and wavelength

Explanation: Entering a medium where the light speed reduces (v = c/n), and wavelength shortens (λ = v/f) while frequency remains unchanged, so both v…