Practice Optics MCQs for KP Revenue Authority (KPRA) Assistant / Inspector Everyday Science — topic-wise sets with solved answers.
Q1. What is the speed of light in a vacuum?
Answer: 3 × 10⁸ m/s
Explanation: The speed of light in a vacuum is exactly 3 × 10⁸ m/s (approximately 300,000 km/s), making it the fastest possible speed in the universe.
Q2. Which color of visible light has the highest frequency?
Answer: Violet
Explanation: In the visible spectrum, violet light has the highest frequency (and shortest wavelength ~380 nm), while red has the lowest frequency (longest wavelength ~700 nm).
Q3. An astronomer studies fine surface details on Jupiter from Earth. Which instrument uses a large objective lens or mirror to collect faint light from distant objects?
Answer: A refracting or reflecting telescope gathers light from celestial objects
Explanation: A telescope uses a large-diameter objective lens (refracting) or concave mirror (reflecting) to gather far more light from a distant object than the naked eye can, then a smaller eyepiece lens magnifies the focused image for detailed observation.
Q4. A chemistry teacher shows students that white light splits into a spectrum through a glass prism. Which simple optical tool separates wavelengths without a diffraction grating machine?
Answer: A spectroscope or prism setup spreads light into its colours
Explanation: A glass prism refracts white light by different amounts for each wavelength (dispersion), separating it into the visible spectrum from red (least refracted) to violet (most refracted).
Q5. A swimmer looking down into a swimming pool from the edge notices the pool appears much shallower than its actual 3-metre depth. This optical illusion occurs because
Answer: light rays from the pool bottom bend away from the normal as they pass from denser water into less dense air causing the apparent position of the bottom to shift upward
Explanation: When light rays travel from the optically denser water to the less dense air, they bend away from the normal at the interface (refraction), so the rays reaching the observer's eye appear to come from a point closer to the surface than the actual bottom.
Q6. In the visible light spectrum, which color has the longest wavelength?
Answer: Red
Explanation: In the visible spectrum, red light has wavelengths of approximately 620-750 nm, the longest of any visible colour. Wavelength and frequency are inversely related (c = fλ), so red also has the lowest frequency among visible colours, while violet has the highest.
Q7. Snell's Law describes the relationship between angles and refractive indices during:
Answer: Refraction of light at an interface between two media
Explanation: Snell's Law (n₁sinθ₁ = n₂sinθ₂) quantifies how a light ray bends when crossing the boundary between two media with different refractive indices, explaining why objects appear shifted when viewed through water or glass.
Q8. The mathematical form of Snell's Law is n₁sinθ₁ = n₂sinθ₂. If light travels from water (n=1.33) into air (n=1.00) and the angle of incidence is 30°, the angle of refraction is approximately:
Answer: 41.7°
Explanation: Applying Snell's Law: 1.33 × sin30° = 1.00 × sinθ₂; sinθ₂ = 1.33 × 0.5 = 0.665; θ₂ = arcsin(0.665) ≈ 41.7°, confirming that light bends away from the normal when moving into a less dense medium.
Q9. Total internal reflection occurs when light travels from a denser medium to a less dense medium and the angle of incidence exceeds:
Answer: The critical angle
Explanation: Total internal reflection occurs when light in a denser medium strikes the boundary with a less dense medium at an angle of incidence greater than the critical angle, causing all the light to be reflected back rather than refracted.
Q10. Optical fibers transmit data using light based on the principle of:
Answer: Total internal reflection
Explanation: When light travels from the dense glass core to the less dense cladding at an angle exceeding the critical angle, it undergoes total internal reflection and stays trapped inside the fibre, allowing lossless transmission over long distances.
Q11. In the visible light spectrum, violet light has an approximate wavelength of:
Answer: 400 nm
Explanation: Violet light sits at the short-wavelength end of the visible spectrum, with wavelengths of approximately 380-450 nm; shorter wavelengths correspond to higher frequency and higher photon energy.
Q12. The acronym ROYGBIV represents the colors of the visible spectrum in order from:
Answer: Longest to shortest wavelength (red to violet)
Explanation: ROYGBIV lists visible spectrum colors from red to violet in order of decreasing wavelength (red ≈ 700 nm, violet ≈ 400 nm) and increasing frequency; red has the longest wavelength and lowest frequency.
Q13. The correct order of the electromagnetic spectrum from lowest to highest frequency is:
Answer: radio, microwave, IR, visible, UV, X-ray, gamma
Explanation: The electromagnetic spectrum ordered from lowest to highest frequency is: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. Frequency and wavelength are inversely related, so this order also runs from longest to shortest wavelength.
Q14. The law of reflection states that the angle of incidence:
Answer: equals the angle of reflection
Explanation: The law of reflection states that when a ray of light hits a smooth surface, the angle of incidence (measured from the normal) equals the angle of reflection (also measured from the normal); this holds for all smooth (specular) reflective surfaces.
Q15. Snell's Law of refraction is expressed as:
Answer: n₁sinθ₁ = n₂sinθ₂
Explanation: Snell's Law describes the relationship between the angles of incidence and refraction when light passes between two media of different refractive indices: n₁sinθ₁ = n₂sinθ₂, where n₁ and n₂ are the refractive indices of the first and second medium respectively, and θ₁ and θ₂ are the angles measured.
Q16. A concave lens always forms an image that is:
Answer: virtual, erect and diminished
Explanation: A concave (diverging) lens spreads light rays outward; it can only form virtual images that appear upright and smaller than the object, located on the same side as the incoming light - regardless of object distance.
Q17. Which type of mirror is used in vehicle rear-view mirrors?
Answer: Convex mirror
Explanation: Convex mirrors curve outward, causing reflected light rays to diverge and producing a virtual, upright, and diminished image that gives a wider field of view - exactly what is needed for rear-view mirrors in vehicles. Concave mirrors converge light and would distort the driver's view of traffic behind.
Q18. Light from the sun reaches Earth in approximately:
Answer: 8 minutes
Explanation: Light travels at approximately 3 × 10⁸ m/s; the average Earth-Sun distance is about 1.496 × 10¹¹ m, giving a travel time of roughly 499 seconds, which is approximately 8.3 minutes - commonly rounded to 8 minutes.
Q19. A convex lens is also known as a:
Answer: converging lens
Explanation: A convex lens is thicker at the centre than at the edges and causes parallel rays of light to converge toward a focal point on the far side, which is why it is called a converging lens.
Q20. Which mirror produces a real and inverted image of an object placed beyond its center of curvature?
Answer: Concave mirror
Explanation: When an object is placed beyond the centre of curvature of a concave mirror (i.e., beyond 2f), reflected rays converge to form a real, inverted image that is smaller than the object on the same side as the object.
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