Level 1
Optics MCQs set 3 for NTS PESCO / HESCO / QESCO / MEPCO Clerk Everyday Science — 20 solved questions.
Q1. Which lens is used to correct myopia (short-sightedness)?
Answer: Concave lens
Explanation: Myopia (short-sightedness) occurs when the eyeball is too long or the cornea too curved, causing parallel light rays to focus in front of the retina. A concave (diverging) lens diverges the incoming rays so that they converge correctly on the retina.
Q2. The colors of the visible spectrum in order from violet to red are remembered by the acronym:
Answer: VIBGYOR
Explanation: VIBGYOR lists the colours of the visible spectrum from shortest wavelength (highest frequency) to longest wavelength: Violet, Indigo, Blue, Green, Yellow, Orange, Red. The reverse acronym ROYGBIV is commonly used to list them from red to violet.
Q3. When light travels from a less dense medium to a more dense medium it:
Answer: Slows down and bends toward the normal
Explanation: When light travels from a less optically dense medium to a more dense medium (e.g., air to glass), it slows down and the refracted ray bends toward the normal. This is described by Snell's law: n₁ sin θ₁ = n₂ sin θ₂.
Q4. Total internal reflection occurs when light travels from a denser medium to a less dense medium at an angle greater than the:
Answer: Critical angle
Explanation: Total internal reflection occurs when light travelling from a denser medium to a less dense medium strikes the boundary at an angle greater than the critical angle, causing all the light to be reflected back into the denser medium with no refraction.
Q5. A convex lens forms a real and inverted image when the object is placed beyond the:
Answer: Focal point
Explanation: A convex (converging) lens produces a real, inverted image only when the object is placed beyond the focal point (further from the lens than one focal length). When the object is between the lens and the focal point, the image is virtual and upright.
Q6. Snell's law relates the angles of incidence and refraction to the refractive indices. If light passes from medium 1 (n=1.0) to medium 2 (n=1.5) at 30° incidence, the refracted angle is approximately:
Answer: 19.47°
Explanation: Applying Snell's law: n₁ sin θ₁ = n₂ sin θ₂ gives 1.0 × sin 30° = 1.5 × sin θ₂, so sin θ₂ = 0.5/1.5 ≈ 0.333 and θ₂ ≈ 19.47°. Light bends toward the normal when entering a denser medium.
Q7. A concave mirror is used in applications requiring a converging beam. Which of the following uses a concave mirror?
Answer: Searchlights and solar cookers
Explanation: A concave mirror reflects parallel rays to converge at a focal point, producing a powerful, directed beam; searchlights use a concave mirror with the light source at the focus to project a collimated beam, and solar cookers use one to concentrate sunlight.
Q8. Ultraviolet radiation lies just beyond which color in the visible spectrum?
Answer: Violet
Explanation: Violet light, with the shortest wavelength (~380-450 nm) in the visible spectrum, sits at the high-frequency end; ultraviolet radiation has even shorter wavelengths and lies just beyond violet, outside the range detectable by the human eye.
Q9. A convex lens is also known as a converging lens. It is used in:
Answer: Cameras, microscopes and magnifying glasses
Explanation: A convex (converging) lens refracts parallel rays to meet at a focal point, making it useful in cameras, microscopes, and magnifying glasses to focus or magnify images. Concave (diverging) lenses are used to correct short-sightedness (myopia) because they spread light rays outward.
Q10. Which instrument spreads white light into a spectrum so colours can be studied separately?
Answer: Prism spectroscope
Explanation: A prism spectroscope uses refraction through a glass or crystal prism to disperse white light into its component wavelengths (colours), since shorter-wavelength violet light is refracted more than longer-wavelength red light. A stethoscope detects body sounds, a seismograph measures ground motion, and an anemometer measures wind speed - none of these produce optical spectra.
Q11. Which optical bench tool magnifies very small nearby objects using an objective lens and eyepiece?
Answer: Compound light microscope
Explanation: A compound light microscope uses a short-focal-length objective lens to form a magnified intermediate image, which is then further magnified by the eyepiece (ocular) lens, achieving total magnifications typically from 40× to 1000×. This two-stage optical design allows examination of cells, bacteria, and fine tissue structures invisible to the naked eye.
Q12. Fizeau’s classic toothed wheel experiment is remembered for timing flashes to estimate which constant?
Answer: Speed of light in air
Explanation: In 1849 Hippolyte Fizeau used a rapidly rotating toothed wheel to chop a light beam into pulses; by measuring the wheel rotation speed at which returning reflected pulses passed back through the gaps, he calculated the first terrestrial estimate of the speed of light (about 3.1 × 10⁸.
Q13. On a clear day the sky appears blue, but near the horizon at sunset it appears red or orange. What phenomenon is responsible for the blue colour of the daytime sky?
Answer: Rayleigh scattering, in which short-wavelength blue light is scattered far more than longer wavelengths
Explanation: Rayleigh scattering describes how light interacts with particles much smaller than its wavelength: the scattering intensity is proportional to the inverse fourth power of wavelength, so short-wavelength blue light scatters roughly ten times more than long-wavelength red light in all directions across the sky.
Q14. Optical fibres in telecommunications carry data as pulses of light over thousands of kilometres with minimal signal loss. Which optical phenomenon keeps the light confined within the fibre?
Answer: Total internal reflection - light strikes the fibre wall at an angle beyond the critical angle and reflects entirely back inward
Explanation: Total internal reflection occurs when light travelling inside a denser medium strikes the boundary with a less dense medium at an angle greater than the critical angle, causing all the light to reflect back inward rather than refracting out.
Q15. A rainbow forms when sunlight passes through raindrops after a shower. Which combination of optical processes produces the coloured arc?
Answer: Refraction on entering the drop, internal reflection at the back, and refraction again on exiting - separating white light into its constituent colours
Explanation: When a ray of sunlight enters a spherical raindrop, it refracts at the air-water boundary, reflects off the inside back surface, and refracts again as it exits; because the refractive index of water varies slightly with wavelength, different colours refract by different amounts, separating white light into a.
Q16. A mirage appears on a hot desert road, making the road appear wet in the distance. Which optical phenomenon is responsible for this illusion?
Answer: Total internal reflection of light from the sky, caused by a layer of extremely hot air near the road surface that has a lower refractive index than cooler air above
Explanation: Near the hot road surface, a layer of air is heated to a very high temperature; this hot air is less dense and has a lower refractive index than the cooler air above.
Q17. The angle of incidence is equal to the angle of reflection. This is the law of:
Answer: Reflection of light
Explanation: The first law of reflection states that the angle of incidence (measured from the normal to the reflecting surface) equals the angle of reflection, and both angles lie in the same plane. Refraction, diffraction, and total internal reflection are separate optical phenomena governed by different laws.
Q18. Total internal reflection occurs when light travels from a denser medium to a rarer medium and the angle of incidence exceeds the:
Answer: Critical angle
Explanation: Total internal reflection occurs when light traveling from a medium of higher refractive index (denser) to one of lower refractive index (rarer) strikes the interface at an angle of incidence greater than or equal to the critical angle, causing all the light to be reflected back into the.
Q19. When light passes from air into glass, it bends towards the normal. This phenomenon is called:
Answer: Refraction
Explanation: Refraction occurs when light passes from one medium to another with a different optical density, causing a change in speed and therefore a change in direction. When light enters glass from air, it slows down and bends toward the normal because glass has a higher refractive index than air.
Q20. A convex (converging) lens is used to correct which vision defect?
Answer: Hypermetropia (long-sightedness)
Explanation: Hypermetropia (long-sightedness) occurs when the eyeball is too short or the lens too flat, causing parallel light rays from distant objects to converge at a focal point behind the retina; a convex (converging) lens placed in front of the eye adds refractive power, shifting the focal point forward.