Where Mindful Learning Begins
Where Mindful Learning Begins
Class 10 Science NCERT Solutions Chapter 9 (CBSE 2026-27) — every in-text question, every embedded Activity question, and all 17 back-of-chapter Exercises on this one page, solved with full working.
Light — Reflection and Refraction opens the physics portion of Class 10 Science and moves from the reflection of light by concave and convex spherical mirrors — the New Cartesian sign convention, the mirror formula, and magnification — to refraction of light at a boundary between two media, refractive index, and finally refraction by convex and concave spherical lenses, the lens formula, and the power of a lens used in eyeglass prescriptions. This is one of the most numerical-heavy chapters in Class 10 Science, and these NCERT solutions work through every Activity-based conceptual question and the full 17-question Exercise set with complete step-by-step working for every calculation, using the sign convention throughout.
Light — Reflection and Refraction is the first physics chapter of Class 10 Science, and it builds two parallel toolkits — one for mirrors, one for lenses — that share the same underlying logic. For spherical mirrors, it works through the pole, centre of curvature, principal focus and focal length, how concave and convex mirrors form different images depending on where the object sits, and how the New Cartesian sign convention turns all of this into one reliable formula (1/v + 1/u = 1/f) and a magnification rule. It then turns to refraction — why a pencil looks bent in water, why a pool looks shallower than it is — and refractive index, before applying the exact same logic to spherical lenses: convex and concave, their own sign convention, the lens formula (1/v − 1/u = 1/f), and finally the power of a lens, the number opticians actually write on a prescription. Every question woven through the chapter is solved here, section by section, in the order the textbook presents it: the four "QUESTIONS" boxes spread across the chapter, the questions embedded directly inside Activities, and the full 17-question Exercise set at the end, with complete numerical working shown for every calculation.
Concave and convex mirrors, ray diagrams, the mirror formula, magnification, and the New Cartesian sign convention.
Why light bends at a boundary between media, Snell's law, and how refractive index relates to the speed of light.
Convex and concave lenses, the lens formula, magnification, and the power of a lens in dioptres.
The principal focus of a concave mirror is the point on its principal axis where a beam of light rays travelling parallel to the principal axis converges (meets) after reflection from the mirror.
A concave mirror — when the object is placed between the pole (P) and the principal focus (F).
A convex mirror always gives an erect (though diminished) image, and it has a wider field of view than a plane mirror of the same size, because of its outward curvature. This lets the driver see a much larger area of traffic behind the vehicle, aiding safe driving.
Since the image is real, magnification m = −3 (negative sign for real image), and u = −10 cm.
The image is located 30 cm in front of the mirror (on the same side as the object), since it is a real image.
The ray bends towards the normal. Water is optically denser than air (has a higher refractive index), and when light travels from a rarer medium (air) to a denser medium (water), it slows down and bends towards the normal.
Highest optical density: Diamond (refractive index 2.42). Lowest optical density: Air (refractive index 1.0003).
Refractive indices: kerosene = 1.44, turpentine oil = 1.47, water = 1.33. Since speed of light (v = c/n) is inversely related to refractive index, light travels fastest in the medium with the lowest refractive index — water (n = 1.33).
This means the speed of light in air (or vacuum) is 2.42 times the speed of light in diamond — light travels 2.42 times faster in air/vacuum than it does inside diamond.
One dioptre (1 D) is the power of a lens whose focal length is 1 metre. 1 D = 1 m−1.
Since the image is real, inverted, and the same size as the object, m = −1 — this happens specifically when the object is at 2F1 (twice the focal length), giving v = 2f = 50 cm.
Since it's a concave lens, f = −2 m (by sign convention).
Looking into the concave (inward-curving) side of the spoon at close range shows a magnified, erect image of your face. Moving the spoon farther away, the image grows larger up to a point, then becomes inverted and diminished beyond the focal point. Looking into the convex (outward-curving) side always shows a diminished, erect image, regardless of distance. This is because the inward-curving surface behaves like a concave mirror (which can give both magnified virtual images up close and real, inverted images from farther away), while the outward-curving surface behaves like a convex mirror (always virtual, erect, diminished).
The image of the pencil in a convex mirror is always erect and diminished, regardless of the pencil's distance from the mirror. As the pencil moves farther away, the image becomes progressively smaller and moves closer to the focus (behind the mirror).
A plane mirror or concave mirror generally cannot show the full-length image of a tall/large nearby object within a small mirror. A convex mirror, however, can show the full-length image of even a large object, because its outward curvature gives it a much wider field of view, letting it fit the whole object into its diminished image — which is why a small convex mirror (like the one at Agra Fort) can capture the full image of a large structure like the Taj Mahal.
No — the extent of the displacement (or apparent raising) effect differs depending on the specific pair of media involved, because each medium has a different refractive index, and the amount of bending of light at the interface depends on this refractive index.
When the slab is placed at an angle (obliquely) to the line, the part of the line under the slab appears bent/displaced at the edges, due to refraction (bending towards the normal entering glass, away from the normal exiting it). When the slab is placed normal (perpendicular) to the line, the line does not appear bent — light travelling along the normal (zero angle of incidence) passes straight through without bending, even though it still changes speed.
It passes straight through into the second medium without any bending or change in direction — the ray continues along the same straight-line path, although its speed changes as it crosses into the new medium.
Answer: (d) Clay — clay is opaque, not transparent, so light cannot pass through it; a lens must be made of a transparent material.
Answer: (d) Between the pole of the mirror and its principal focus.
Answer: (b) At twice the focal length (2F1).
Answer: (a) both concave — a negative focal length by sign convention corresponds to a concave mirror and a concave lens alike.
Answer: (d) either plane or convex — both always give erect images regardless of object distance; a concave mirror only gives an erect image when the object is between the pole and focus.
Answer: (c) A convex lens of focal length 5 cm — a convex (magnifying) lens with a short focal length gives greater magnification when the object is placed within the focal length.
For a concave mirror to produce an erect image, the object must be placed between the pole (P) and the focus (F) — object distance between 0 and 15 cm in front of the mirror.
Nature of image: virtual, erect, and enlarged (larger than the object).
Ray diagram:
Both reflected rays diverge in front of the mirror; extending them backward (dashed) locates the virtual, erect, enlarged image behind the mirror.
(a) Headlights: Concave mirror — placing the bulb at the principal focus produces a powerful, parallel beam of light for illuminating the road.
(b) Side/rear-view mirror: Convex mirror — always gives an erect, diminished image with a wider field of view, letting the driver see more of the traffic behind.
(c) Solar furnace: Concave mirror (large) — converges parallel rays of sunlight to a sharp focus, producing intense heat at that point.
Yes, the lens will still form a complete image, though dimmer than before. Every unobstructed part of the lens still receives light rays from every point of the object and refracts them towards the image — covering half the lens only blocks half the rays reaching each image point, reducing the image's brightness/intensity, but the remaining half of the lens can still converge rays from every point of the object to form the complete image.
Given: h = +5 cm, u = −25 cm, f = +10 cm (convex lens)
The image is real, inverted, diminished, formed about 16.7 cm on the other side of the lens, with a height of about 3.3 cm.
Ray diagram:
Both real rays converge on the far side of the lens, giving a real image that can be captured on a screen.
Given: f = −15 cm, v = −10 cm (concave lens, virtual image on same side as object)
The object is placed 30 cm from the lens.
Ray diagram:
A concave lens always diverges rays — the image is located by extending the real, diverging rays backward until they meet, on the object's own side of the lens.
Given: u = −10 cm, f = +15 cm (convex mirror)
Since v is positive, the image is virtual, formed 6 cm behind the mirror.
Since m is positive and less than 1: the image is virtual, erect, and diminished.
The positive sign means the image is virtual and erect, and the magnitude of 1 means the image is exactly the same size as the object — consistent with the known properties of a plane mirror's image (always virtual, erect, same size).
Given: h = +5.0 cm, u = −20 cm, R = +30 cm, so f = R/2 = +15 cm
The image is formed about 8.6 cm behind the mirror, is virtual, erect, diminished, with a height of about 2.1 cm.
Given: h = +7.0 cm, u = −27 cm, f = −18 cm (concave mirror)
The screen should be placed 54 cm in front of the mirror.
The image is real, inverted, and enlarged (twice the object size), with a height of 14.0 cm.
Since the focal length is negative, this is a concave (diverging) lens.
Since the power (and focal length) is positive, this is a convex (converging) lens.
Next up is Chapter 10 — The Human Eye and the Colourful World. Or explore the full chapter list, browse the Class 10 Science hub, or book a free demo class for personalised coaching.
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