1.A light‑year is a measure of:
A) Speed
B) Distance
C) Time
D) Velocity
Answer: B) Distance
Explanation: A light‑year is the distance that light travels in vacuum in one Julian year (~365.25 days). It is not a measure of time or speed.
2. Which portion of the electromagnetic spectrum can be perceived by the human eye?
A) Between 400 nm and 700 nm
B) Between 40 nm and 70 nm
C) Between 400 nm and 7000 nm
D) Between 4 nm and 700 nm
Answer: A) Between 400 nm and 700 nm
Explanation: Visible light ranges approximately from 400‑700 nanometres; wavelengths shorter than ~400 nm are ultraviolet, longer than ~700 nm are infrared.
3.When white light passes through a prism, which of the following happens to the light ray of shortest wavelength?
A) Accelerated and refracted the most
B) Slowed down and refracted the most
C) Accelerated and refracted the least
D) Slowed down and refracted the least
Answer: B) Slowed down and refracted the most
Explanation: In dispersive media, shorter wavelength light (e.g., violet) slows down more relative to vacuum (higher refractive index) and bends more (higher refraction) than longer wavelengths.
4.In a plane mirror:
A) The image formed is real and inverted
B) The image is virtual, erect, same size as object
C) The focal length is finite (non‑infinite)
D) It converges parallel rays of light
Answer: B) The image is virtual, erect, same size as object
Explanation: Plane mirrors form virtual images (you cannot project them on screen), erect (upright) and the image appears as far behind the mirror as the object is in front, of same size. The focal length of a plane mirror is effectively infinite; it does not converge parallel rays.
5.What is the focal length of a concave lens with power −5 D?
A) −5 m
B) −5 cm
C) −20 cm
D) −0.2 m
Answer: D) −0.2 m
Explanation: Power 
(in metres) so 
. Negative for concave lens.
6.Which phenomenon is responsible for the blue color of the daytime sky?
A) Absorption
B) Scattering
C) Reflection
D) Refraction
Answer: B) Scattering
Explanation: Rayleigh scattering of sunlight by molecules in the atmosphere scatters shorter wavelengths (blue) more strongly, so sky appears blue.
7.Total internal reflection occurs when light travels from:
A) A rarer to a denser medium
B) A denser to a rarer medium at angle greater than critical angle
C) Vacuum to any medium
D) Medium with lower refractive index into one with higher refractive index
Answer: B) A denser to a rarer medium at angle greater than critical angle
Explanation: Total internal reflection happens only when going from optically denser medium to a less dense medium, and when angle of incidence exceeds the critical angle.
8.A concave mirror produces a virtual, erect, magnified image. Where must the object be placed?
A) At the centre of curvature
B) Between the centre of curvature and the focus
C) Between focus and the pole of the mirror
D) At infinity
Answer: C) Between focus and the pole of the mirror
Explanation: When object is between focal point (F) and the mirror’s surface (pole), concave mirror gives virtual, erect, magnified image. If object farther, image becomes real etc.
9.What kind of lens is used in movie projectors (to project large image on screen)?
A) Concave lens
B) Convex lens
C) Meniscus lens
D) Cylindrical lens
Answer: B) Convex lens
Explanation: Convex (converging) lens is used to project light to form image on screen; the lens brings diverging rays to converge onto screen forming real image.
10.If all colors of white light are reflected by a surface, the surface appears:
A) Black
B) White
C) Grey
D) Opaque
Answer: B) White
Explanation: White light is sum of all visible colors. If none are absorbed, all are reflected, making it appear white. Black means none reflected (all absorbed).
11.The magnifying power of a telescope can be increased by:
A) Decreasing the focal length of the eyepiece
B) Increasing the diameter of the objective
C) Reducing the focal length of the objective
D) Increasing the diameter of the eyepiece
Answer: A) Decreasing the focal length of the eyepiece
Explanation: Angular magnification ≈ focal length of objective / focal length of eyepiece. Smaller eyepiece focal length → higher magnification. Increasing objective diameter improves light gathering (brightness, resolution) but doesn’t directly increase magnification.
12.Which of these waves cannot be polarized?
A) Light waves
B) Water surface waves
C) Longitudinal sound waves
D) Electromagnetic waves
Answer: C) Longitudinal sound waves
Explanation: Polarization refers to orientation of oscillations in transverse waves. Longitudinal waves oscillate in direction of propagation, so cannot be polarized.
13.What is the appearance of the sky to an observer on the Moon during lunar day?
A) Blue
B) Black
C) Light yellow
D) Orange
Answer: B) Black
Explanation: The Moon has virtually no atmosphere, so there is no scattering of sunlight; thus the sky remains black even when the surface is lit by Sun.
14.Which eye defect causes image focus in front of the retina?
A) Myopia
B) Hyperopia
C) Astigmatism
D) Presbyopia
Answer: A) Myopia
Explanation: In myopia (nearsightedness), the eyeball is too long or focal length too short, so parallel rays focus before the retina. Hyperopia is opposite: focus behind retina.
15.The refractive index of a medium is 
. Which relation between angle of incidence 
and refraction 
is correct?
A) 
B)
C) 
D)
Answer: A)
Explanation: By Snell’s law, 
. So 
.
16.How far must an object be placed in front of a convex lens of focal length 20 cm so that the image formed is diminished (smaller than the object)?
A) 10 cm
B) At infinity
C) Just beyond 2F (i.e., > 40 cm)
D) Between F and 2F
Answer: C) Just beyond 2F (i.e., > 40 cm)
Explanation: For a convex lens: if object is beyond 2F, image is real, inverted, diminished (smaller). Between F and 2F image is magnified; at 2F same size; at infinity highly diminished.
17.We see lightning before hearing thunder because:
Answer: D) Both A & C
Explanation: Light travels extremely fast (≈ 3×10⁸ m/s) while sound in air is much slower (~343 m/s), so we see light first. Also, sound’s slower travel contributes.
18.Which of the following statements about the eye is correct?
A) The image formed on retina is virtual and erect
B) The image is real and inverted
C) The eye lens is concave in shape
D) Eye defect treated by convex lens is myopia
Answer: B) The image is real and inverted
Explanation: The lens of the eye is convex; it forms a real, inverted, diminished image on the retina, which brain interprets as erect. Myopia is treated by concave lens; hyperopia by convex.
19.If the power of a lens is −2 D, what is its focal length?
A) −0.5 m
B) −1 m
C) +0.5 m
D) +1 m
Answer: A) −0.5 m
Explanation: (in metres). So 
m. Negative indicates diverging (concave) lens.
20.Which phenomenon causes golden shine seen in some sea shells?
A) Diffraction
B) Dispersion
C) Polarization
D) Reflection
Answer: C) Polarization
Explanation: The golden shine (iridescence) in shells often arises from tiny layers (microstructure) that cause interference and selective polarization; the polarized light reflections make some colors more intense. (Some sources may attribute interference + reflection; but commonly polarization plays a role in color effects due to microstructure.)
21.A beam of white light is incident on a glass prism. Which color emerges deviated the least?
A) Violet
B) Blue
C) Red
D) Green
Answer: C) Red
Explanation: Red light has the longest wavelength in visible spectrum and is refracted the least (lower dispersion), so least deviation.
22.If the refractive index of medium A w.r.t medium B is 1.5, then the refractive index of B w.r.t A is:
A) 1.5
B) 2/3
C) √(1.5)
D) (1.5)²
Answer: B) 2/3
Explanation: 
23.A convex mirror always forms:
A) A real, inverted image
B) A virtual, erect image
C) A virtual, inverted image
D) A real, erect image
Answer: B) A virtual, erect image
Explanation: Convex mirrors diverge rays; image is always virtual (behind mirror), erect (upright), and smaller than object.
24.The critical angle for water‑air interface is ~48°. If light inside water strikes the surface at 60°, what happens?
A) Refraction into air
B) Total internal reflection
C) Partial reflection and partial refraction
D) Absorption
Answer: B) Total internal reflection
Explanation: Angle of incidence > critical angle yields total internal reflection.
25.In Young’s double slit experiment: fringe width is directly proportional to:
A) slit separation
B) wavelength
C) distance between slits and screen
D) both B and C
Answer: D) both B and C
Explanation: Fringe width 
. So increases with wavelength (λ) and distance to screen (D), inversely with slit separation (d).
26.A lens has focal length 15 cm. If an object is placed at 30 cm, the image distance (for a convex lens) is:
A) 30 cm
B) 15 cm
C) 10 cm
D) 20 cm
Answer: D) 20 cm
Explanation: Using lens formula: 
. Here f=15 cm, u = −30 cm → 
. So v = 30 cm. Actually wait, sign conventions: if object at 30 cm, image distance comes out positive 30 cm. But that suggests answer A. But if using standard object distance = +30, get v = 30. But common convention uses u negative so v positive. So correct answer: A) 30 cm.
27.If a convex lens is dipped in a medium having the same refractive index as the lens material, its focal length becomes:
A) 0
B) Infinite
C) Very small non‑zero
D) Unchanged
Answer: B) Infinite
Explanation: When lens and surrounding medium have same refractive index, lens has no bending power; behaves as if focal length infinite.
28.Which of these colors has the shortest wavelength in visible spectrum?
A) Green
B) Red
C) Violet
D) Yellow
Answer: C) Violet
Explanation: Violet ≈ 400 nm (short end), then blue, green, yellow, red.
29.An object at infinity is observed by eye. Where is the image formed?
A) On the retina
B) Behind the retina
C) In front of the retina
D) Does not form an image
Answer: A) On the retina
Explanation: For relaxed eye, rays from infinity are focused on the retina.
30.The power of accommodation in human eye refers to:
A) Ability to see far objects
B) Ability to adjust lens focal length to see objects at different distances
C) Ability to focus only at a fixed distance
D) Power of eye lens only
Answer: B) Ability to adjust lens focal length to see objects at different distances
Explanation: Accommodation is ciliary muscles adjusting the focal length so seen objects at various distances.
31.Which optical instrument uses two convex lenses to magnify distant objects?
A) Microscope
B) Telescope
C) Magnifying glass
D) Spectrometer
Answer: B) Telescope
Explanation: Refracting telescope uses objective convex lens + eyepiece to magnify distant objects.
32.If for a convex lens, object is placed at 2F (twice focal length), then image will be:
A) At F
B) At 2F
C) Between F and 2F
D) At infinity
Answer: B) At 2F
Explanation: Object at 2F produces image of equal size at 2F on other side.
33.In diffraction of light through a single slit, as slit width decreases, the central maximum becomes:
A) Narrower and brighter
B) Wider and dimmer
C) Wider and brighter
D) Narrower and dimmer
Answer: B) Wider and dimmer
Explanation: Narrower slit → more diffraction → central maximum spreads (wider), amplitude falls → dimmer.
34.Polarization of light can occur by:
A) Reflection
B) Refraction
C) Scattering
D) All of the above
Answer: D) All of the above
Explanation: Light becomes polarized by reflection at certain angles (Brewster’s law), by scattering, and selective absorption etc.
35.Which is NOT true about Huygens’ principle?
A) Every point on a wavefront acts as source of secondary wavelets
B) Wavefront is envelope of secondary wavelets
C) Works for reflection and refraction
D) Wavelets always spherical in shape
Answer: D) Wavelets always spherical in shape
Explanation: In general medium, wavelets are spherical; but if medium is anisotropic or in certain geometries, shape may differ. Also some interpretations say “always” spherical is too restrictive.
36.The resolving power of microscope increases if:
A) Wavelength of illumination increases
B) Numerical aperture decreases
C) Numerical aperture increases
D) Eyepiece focal length increases
Answer: C) Numerical aperture increases
Explanation: Resolving power ∝ NA / λ. Higher NA gives better resolution; shorter λ also helps.
37.A light ray passes from air into water (n≈1.33). What happens to its speed, wavelength, and frequency?
A) Speed and wavelength decrease; frequency remains same
B) Speed increases; wavelength decreases; frequency changes
C) Speed decreases; wavelength increases; frequency remains same
D) All three change
Answer: A) Speed and wavelength decrease; frequency remains same
Explanation: Frequency is an invariant when crossing boundary; speed in medium = c / n; wavelength = (speed)/frequency → lower.
38.Which phenomenon is used in “mirage” formation?
A) Total internal reflection
B) Refraction due to gradient of air density
C) Reflection from ground
D) Diffraction
Answer: B) Refraction due to gradient of air density
Explanation: Mirage is caused by refractive index changing with height (air temperature gradient), bending light rays; in some cases total internal reflection happens at surface of hot ground.
39.The focal length of a combination of two thin lenses in contact is given by:
A) f₁ + f₂
B) (f₁ + f₂) / (f₁ f₂)
C) (f₁ f₂) / (f₁ + f₂)
D) f₁ f₂
Answer: C) (f₁ f₂) / (f₁ + f₂)
Explanation: Lens formula for thin lenses in contact: 
→ f = (f₁f₂)/(f₁ + f₂)
40.If the power of a lens is +4 diopters, its focal length is:
A) +0.25 m
B) +4 m
C) −0.25 m
D) +0.04 m
Answer: A) +0.25 m
Explanation: Power P = 1/f (in metres) → f = 1/4 = 0.25 m.
41.Which optical phenomenon explains the colorful rings seen around a street lamp through a foggy or misty atmosphere?
A) Diffraction
B) Dispersion
C) Polarization
D) Total internal reflection
Answer: A) Diffraction
Explanation: Fine particles cause diffraction of light and interference, forming rings around light sources in mist/fog.
42.Which of the following is a coherent source of light?
A) Two different lamps
B) Laser
C) Light from sun and moon
D) Reflected light from wall
Answer: B) Laser
Explanation: Coherent light has constant phase difference and same frequency; laser is a good example.
43.In a refraction experiment, if angle of incidence in air is 30° and refractive index of glass is 1.5, what is angle of refraction?
(use Snell’s law)
A) ~19.5°
B) ~20°
C) ~45°
D) ~30°
Answer: A) ~19.5°
Explanation: 
. Here 1×sin30° = 1.5 × sin θ₂ → sin θ₂ = (0.5)/(1.5) ≈0.333 → θ₂ ≈19.5°.
44.The phenomenon of splitting of white light into its constituent colours is called:
A) Dispersion
B) Diffraction
C) Polarization
D) Scattering
Answer: A) Dispersion
Explanation: Dispersion = dependence of refractive index on wavelength, causing different bending.
45.Which one of these is NOT a requirement for producing interference patterns?
A) Coherent sources
B) Monochromatic light
C) Small slit sizes comparable to wavelength
D) Thick screen
Answer: D) Thick screen
Explanation: Thickness of screen is irrelevant; what matters are coherence, monochromaticity, slit and separation conditions.
46.In which case will the image formed by a concave mirror be enlarged?
A) Object beyond centre of curvature
B) Object at centre of curvature
C) Object between focus and centre of curvature
D) Object at focus
Answer: C) Object between focus and centre of curvature
Explanation: For concave mirror, object between F and C → image real, inverted, enlarged. If at C, image same size; beyond C, diminished.
47.A ray of light inside a medium strikes boundary at the critical angle. What angle does the refracted ray make with the boundary?
A) 90°
B) 0°
C) Equal to critical angle
D) Depends on medium
Answer: A) 90°
Explanation: At critical angle, refracted ray grazes along boundary, i.e., at 90° to normal.
48.What is the effect on diffraction pattern of single slit when wavelength increases?
A) More fringes appear, central maxima narrower
B) Central maxima becomes wider, fringes more separated
C) Pattern disappears
D) No change
Answer: B) Central maxima becomes wider, fringes more separated
Explanation: Diffraction width ∝ λ, so increasing λ spreads pattern.
49.Which of the following is a longitudinal wave?
A) Light wave
B) Sound wave
C) Water surface wave
D) Electromagnetic wave
Answer: B) Sound wave
Explanation: Longitudinal: oscillations parallel to direction of propagation; sound in air is one.
50.The image formed by convex lens for object at focal point is:
A) At infinity
B) At object itself
C) Between lens and focal point
D) Virtual and erect
Answer: A) At infinity
Explanation: When object placed at focal point, light rays exit parallel and image forms at infinity.
51.What happens to the refracted light when it passes from medium with lower optical density to higher optical density?
A) It bends away from normal
B) It bends towards normal
C) It continues straight
D) Total internal reflection occurs
Answer: B) It bends towards normal
Explanation: When going into denser medium (higher refractive index), light slows and bends towards normal.
52.An optical fibre uses which phenomenon to transmit light along its length?
A) Refraction
B) Diffraction
C) Total internal reflection
D) Polarization
Answer: C) Total internal reflection
Explanation: Light is totally internally reflected within the fibre if incidence angles are above critical, allowing transmission with little loss.
53.The sky appears reddish during sunrise and sunset because:
A) Dispersion
B) Scattering of longer wavelengths
C) Scattering of shorter wavelengths
D) Absorption of shorter wavelengths
Answer: C) Scattering of shorter wavelengths
Explanation: At sunrise/sunset, sunlight passes through thicker atmosphere: blue/violet scattered out, leaving red/orange. So the scattering of shorter (blue) removes those colours; longer wavelengths dominate.
54.Which of the following will give maximum resolving power for telescope?
A) Small objective diameter, small focal length
B) Large objective diameter
C) Eyepiece focal length large
D) Eyepiece focal length small
Answer: B) Large objective diameter
Explanation: Resolving power for telescope ~ (objective diameter) / wavelength. Bigger diameter → higher resolution.
55.In Young’s double slit experiment, if one of the slits is covered partially (transmits only half intensity), the interference pattern’s contrast (visibility) will:
A) Increase
B) Decrease
C) Remain same
D) Disappear
Answer: B) Decrease
Explanation: Visibility = (I_max − I_min)/(I_max + I_min). If amplitudes differ, I_min increases → contrast lowers.
56.Mirror whose surface is curved inward is called:
A) Convex mirror
B) Concave mirror
C) Plane mirror
D) Spherical mirror
Answer: B) Concave mirror
Explanation: “Curved inward” means the reflecting surface curves inward (like inside of a bowl) — concave.
57.Which statement is true for light traveling in vacuum?
A) It travels slower than in glass
B) Its speed depends on wavelength
C) Its speed is constant (c) for all wavelengths
D) Its frequency changes upon entering a medium
Answer: C) Its speed is constant (c) for all wavelengths
Explanation: In vacuum, light speed is constant (~3×10⁸ m/s) independent of wavelength; frequency remains constant when entering a medium.
58.If an object placed between focus (F) and mirror/pole of a concave mirror, the image is:
A) Real, inverted
B) Virtual, erect
C) At infinity
D) Diminished
Answer: B) Virtual, erect
Explanation: For concave mirror, object between F and pole gives virtual, upright, magnified image.
59.Which of these optical devices reduce aberration in lenses?
A) Using thicker lenses
B) Using combination of lens types (achromatic doublet)
C) Using single thin convex lens only
D) Increasing aperture
Answer: B) Using combination of lens types (achromatic doublet)
Explanation: Achromatic doublets combine convex + concave lenses of different glass to reduce chromatic aberration.
60.If the slit separation in Young’s experiment is doubled, fringe width will:
A) Double
B) Halve
C) Remain same
D) Increase by factor √2
Answer: B) Halve
Explanation: Fringe width 
. If d doubles, β halves (D, λ constant).
61.A beam of unpolarized light falls on a glass surface at Brewster’s angle. The reflected light is:
A) Unpolarized
B) Completely polarized parallel to surface
C) Completely polarized perpendicular to surface
D) Partially polarized
Answer: B) Completely polarized parallel to surface
Explanation: At Brewster’s angle, reflected ray is fully polarized with electric vector perpendicular to the plane of incidence (i.e., parallel to surface).
62.
A) Virtual and erect
B) Real and inverted
C) At infinity
D) No image
Answer: A) Virtual and erect
Explanation: Object inside focus (10 < 15) → image virtual, upright, enlarged behind mirror.
63.Which of the following phenomena requires light to behave like a wave?
A) Photoelectric effect
B) Compton scattering
C) Diffraction
D) Photo-luminescence
Answer: C) Diffraction
Explanation: Diffraction, interference require wave nature. Photoelectric & Compton show particle nature.
64.When light passes from air into glass, which of the following changes?
A) Speed of light decreases
B) Frequency decreases
C) Wavelength increases
D) Frequency increases
Answer: A) Speed of light decreases
Explanation: Speed decreases; frequency remains same; wavelength decreases.
65.The apparent depth of a pool of water is 2 m. The real depth is 2.5 m. The refractive index of water relative to air is:
A) 1.25
B) 0.8
C) 1.5
D) 1.2
Answer: C) 1.25 or similar? Actually apparent depth / real depth = 2 / 2.5 = 0.8 → refractive index = real/apparent = 2.5 / 2 = 1.25.
So Answer: A) 1.25
Explanation: Refractive index = real depth / apparent depth.
66.A person 6 ft tall wishes to see his whole image in a plane mirror. The mirror must be at least what height and where placed?
A) Height half his height, anywhere in room
B) Half his height, lower edge at waist level
C) Full height, lower edge on floor
D) Half height, placed such that top of mirror is halfway between his eyes and top of head
Answer: A) Half his height, anywhere in front (lower edge at some appropriate height)
Explanation: A plane mirror of half the object height is sufficient to see whole body, since rays from feet & head reflect appropriately.
67.Which of these statements about electromagnetic spectrum is correct?
A) Gamma rays have longer wavelengths than radio waves
B) Visible light has shorter wavelength than ultraviolet
C) Infrared has longer wavelength than visible light
D) Microwave has shorter wavelength than ultraviolet
Answer: C) Infrared has longer wavelength than visible light
Explanation: Ordering wavelength from small to large: gamma < X < UV < visible < infrared < microwaves < radio.
68.In the photoelectric effect, if intensity of incident light doubles (wavelength unchanged), which happens?
A) Number of photoelectrons increases
B) Kinetic energy of photoelectrons increases
C) Threshold frequency changes
D) Both B & C
Answer: A) Number of photoelectrons increases
Explanation: Intensity ↑ gives more photons per unit time → more electrons emitted. KE per photoelectron depends on photon energy (wavelength), not intensity.
69.Which among the following is TRUE regarding a concave lens?
A) Always forms real image
B) Same as convex mirror
C) Diverging lens: always virtual image
D) Converging effect
Answer: C) Diverging lens: always virtual image
Explanation: Concave lens diverges light, gives virtual, erect, diminished image no matter object position.
70.If a convex mirror is used, as object moves further away, the image formed:
A) Moves closer to mirror pole
B) Moves further back behind mirror
C) Size increases
D) Becomes real
Answer: A) Moves closer to mirror pole
Explanation: For convex mirror, image distance (virtual) decreases in magnitude (image moves closer to mirror) as object distance increases; size decreases.
71.The phenomenon responsible for “twinkling of stars” is:
A) Reflection
B) Refraction
C) Diffraction
D) Scattering
Answer: B) Refraction
Explanation: Twinkling caused by atmospheric refraction; variations in refractive index cause the star’s image to shift and vary in brightness.
72.Which of these optical paths has maximum time of travel for light?
A) Straight line path in vacuum
B) Slightly curved path in medium of high refractive index
C) Longer path in lower refractive index
D) Same path but making zig‑zag
Answer: B) Slightly curved path in medium of high refractive index
Explanation: Time = path length × (n / c). High n slows light; so even if path short, a medium with high refractive index can take more time.
73.The resolving power of a grating is given by:
A) N*m (number of slits × order)
B) (λ / d)
C) (d / λ)
D) (1 / number of slits)
Answer: A) N*m
Explanation: Resolving power R = N * m, where N = number of slits illuminated, m = diffraction order.
74.Colour of thin oil film seen is from constructive interference. If thickness of film increases gradually, observed colour will shift toward:
A) Red end (longer λ)
B) Blue end (shorter λ)
C) Violet only
D) No shift
Answer: A) Red end (longer λ)
Explanation: With larger path difference, constructive interference happens for larger wavelengths → colour shifts toward red.
75.Light from two coherent sources superpose. If their phase difference is π, then at that point intensity is:
A) Maximum
B) Minimum (zero)
C) Half of maximum
D) Dependent on amplitudes
Answer: B) Minimum (zero)
Explanation: Phase difference π (180°) → destructive interference if amplitudes equal → zero intensity.
76.In a rainbow, primary rainbow’s angular radius is about:
A) 30°
B) 42°
C) 50°
D) 90°
Answer: B) 42°
Explanation: Primary rainbow radius ~42° for red; inner violet around ~40°.
77.Which of these instruments uses a combination of lenses so one lens corrects chromatic aberration of another?
A) Simple magnifier
B) Achromatic telescope (uses achromatic lenses)
C) Concave mirror telescope
D) Pinhole camera
Answer: B) Achromatic telescope
Explanation: Achromatic doublet uses two lens elements made from glasses with different dispersion to reduce chromatic aberration.
78.A prism only disperses light when its refractive index depends on:
A) Temperature
B) Wavelength
C) Pressure
D) Angle
Answer: B) Wavelength
Explanation: Dispersion arises because refractive index varies with wavelength.
79.Which factor does not affect speed of light in a medium?
A) Refractive index of medium
B) Wavelength of light (in medium)
C) Temperature of medium (if it changes refractive index)
D) Intensity of light
Answer: D) Intensity of light
Explanation: Speed depends on medium’s properties (n), possibly temperature etc, but not on light’s intensity.
80.Which of the following is true about virtual images?
A) Can be projected on a screen
B) Formed by converging rays
C) Formed when diverging rays appear to come from a point
D) Always inverted
Answer: C) Formed when diverging rays appear to come from a point
Explanation: Virtual images are where light doesn’t actually converge, but appears to diverge from a point behind or within device. They are erect typically; can’t project them.
81.Light behaves like waves according to which theory?
A) Newton’s corpuscular theory
B) Huygens’ wave theory
C) Bohr’s atomic model
D) Einstein’s photoelectric effect
Answer: B) Huygens’ wave theory
Explanation: Huygens described light propagation via wavefronts and secondary wavelets.
82. If monochromatic light of wavelength 600 nm is used in Young’s double slit with slit separation 0.5 mm and screen distance 1 m, the fringe width is:
A) 1.2 mm
B) 1.0 mm
C) 0.6 mm
D) 0.5 mm
Answer: A) 1.2 mm
Explanation: β = (λ D)/d = (600×10⁻⁹ * 1) / (0.5×10⁻3) = (600×10⁻⁹)/(5×10⁻4) = 1.2×10⁻3 m = 1.2 mm.
83.Which of the following statements about mirrors is false?
A) In a plane mirror, image distance = object distance
B) Convex mirror always gives erect image
C) Concave mirror always gives virtual image
D) Mirror line of symmetry is the principal axis
Answer: C) Concave mirror always gives virtual image
Explanation: False: A concave mirror can give real images if object is outside focal length; only when object is inside focal length it gives virtual image.
84.The angle between refracted and reflected ray when light hits glass at 0° incidence is:
A) 0°
B) 90°
C) 180°
D) Depends on refractive index
Answer: A) 0°
Explanation: At normal incidence, light goes straight into the medium (refracted ray continues normal), reflected ray is back along same path — the angle between them is 0° or 180° depending convention, but essentially no deviation.
85.Light is incident at the Brewster angle on a glass slab. Which of these is true?
A) Reflected and refracted rays are at right angles
B) Reflected ray is parallel to refracted ray
C) Reflected light is unpolarized
D) Refracted light is absent
Answer: A) Reflected and refracted rays are at right angles
Explanation: At Brewster’s angle, reflected and refracted rays are perpendicular.
86.Which of the following is NOT a type of aberration in lenses/mirrors?
A) Spherical aberration
B) Chromatic aberration
C) Comatic aberration
D) Geometric aberration
Answer: D) Geometric aberration
Explanation: Common aberrations: spherical, chromatic, coma (comatic), astigmatism etc. “Geometric aberration” is generic and not standard type by that name.
87.If image formed by a convex lens is same size as object, then object is placed at:
A) Focal point
B) Centre of curvature (2F)
C) Between F and 2F
D) Beyond 2F
Answer: B) Centre of curvature (2F)
Explanation: Object at 2F gives image at 2F same size.
88.In a prism, angle of minimum deviation depends on:
A) Wavelength of light
B) Refractive index
C) Apex angle of prism
D) All above
Answer: D) All above
Explanation: Minimum deviation depends on wavelength (since refractive index depends on it), prism’s apex angle, and refractive index.
89.What is the image produced by a concave mirror when object is at infinity?
A) At F, real, inverted, very small
B) At C, real, inverted
C) Virtual, erect at infinity
D) No image
Answer: A) At F, real, inverted, very small
Explanation: Rays parallel to principal axis converge at focal point; image is very small (point) at F.
90.Which of these optical phenomena cannot be explained by geometrical optics?
A) Reflection
B) Refraction
C) Interference
D) Formation of images by lenses
Answer: C) Interference
Explanation: Interference arises from wave nature; geometrical optics treats light as rays and cannot explain interference, diffraction, polarization fully.
91.The principle that light takes path of least time through two points is called:
A) Fermat’s principle
B) Huygens’ principle
C) Snell’s law
D) Law of reflection
Answer: A) Fermat’s principle
Explanation: Fermat’s principle: light travels between two points in such a way that the travel time is minimal (or stationary).
92.In double slit, if path difference is 2.5 λ, what is phase difference?
A) 2.5 π
B) 5 π
C) π/2
D) 5π/2
Answer: D) 5π/2
Explanation: Phase difference = (2π / λ) × path difference = (2π/λ) * (2.5 λ) = 5π.
93.Which type of mirror is used in car rear‑view mirrors (wide angle)?
A) Plane mirror
B) Convex mirror
C) Concave mirror
D) Parabolic mirror
Answer: B) Convex mirror
Explanation: Convex mirror gives erect, diminished image and wide field of view.
94.What happens to the image when an object approaches a concave mirror from outside 2F to F?
A) Image moves between F and C and gets larger
B) Image stays fixed
C) Image moves towards infinity
D) Image becomes virtual
Answer: A) Image moves between F and C and gets larger
Explanation: As object moves from 2F toward F, image forms beyond 2F to beyond C and magnifies.
95.The photoelectric effect demonstrates which property of light?
A) Wave nature
B) Particle nature
C) Both wave and particle nature
D) Neither
Answer: B) Particle nature
Explanation: Photoelectric effect shows quantization: light photons, threshold frequency etc.
96.If slit separation in Young’s experiment is 1 mm, screen distance D = 2 m, wavelength = 500 nm, what is separation between 2nd and 3rd bright fringe?
A) (2 * λD)/d
B) (3 * λD)/d
C) ( (3−2) * λD )/d = λD/d
Which numerically = (1 × 10⁻6 * 2) / (1 × 10⁻3) = 2 × 10⁻3 m = 2 mm
So Answer: ~2 mm
97.Which of the following devices uses interference to produce coloured patterns?
A) Pinhole camera
B) Soap film
C) Convex mirror
D) Concave lens
Answer: B) Soap film
Explanation: Thin films produce interference between reflections from two surfaces → coloured fringes.
98.If a light ray in glass (n=1.5) hits boundary with air at angle 50°, will total internal reflection occur?
A) Yes, since critical angle ~41°
B) No, since angle < critical angle
C) Yes, since angle > critical angle
D) Cannot say
Answer: C) Yes, since angle > critical angle
Explanation: Critical angle for glass–air ≈ arcsin(1/1.5) ≈41°. 50° > 41° → total internal reflection.
99.Which phenomenon is exploited in the operation of a focusing telescope?
A) Refraction only
B) Reflection only
C) Reflection + refraction
D) Diffraction
Answer: C) Reflection + refraction
Explanation: Many telescopes use mirrors (reflection) or combination with lenses (refraction). For refracting telescopes, refraction; for reflecting telescopes, reflection; many modern use both in designs.
100.If a monochromatic light source is placed at the centre of a hollow glass sphere in air, what will observer see?
A) No light
B) Light beam refracted out
C) Light from all directions due to reflection inside glass
D) Light escapes at various points by refraction
Answer: D) Light escapes at various points by refraction
Explanation: Rays inside the sphere will undergo refraction at the glass‑air interface depending on incidence angle; many rays exit, though internal reflections may also occur depending on geometry.