What are the laws of reflection and how do they apply to mirrors?

The laws of reflection govern how light bounces off a surface. The first law states that the angle of incidence (angle between the incident ray and normal) equals the angle of reflection (angle between the reflected ray and normal). The second law states that the incident ray, reflected ray, and normal at the point of incidence all lie in the same plane. These laws apply to both plane mirrors and curved mirrors. In a plane mirror, the image is virtual (cannot be projected on a screen), erect, of the same size, and laterally inverted (left-right reversed). Concave mirrors follow these laws too — they form different types of images (real or virtual) depending on the object's position. Concave mirrors are used in torches and headlights because they converge reflected light into a beam.

What is the difference between a concave and convex mirror and their uses?

A concave mirror (converging mirror) has its reflecting surface curved inward, like the inside of a spoon. It can form both real and virtual images depending on where the object is placed. When the object is beyond the centre of curvature, a real, inverted, and diminished image is formed. When the object is between the pole and focus, a virtual, erect, and magnified image is formed. Concave mirrors are used in torches, searchlights, solar furnaces, and as shaving or make-up mirrors. A convex mirror (diverging mirror) has its reflecting surface curved outward. It always forms a virtual, erect, and diminished image regardless of the object's position. This gives a wider field of view, which is why convex mirrors are used as rear-view mirrors in vehicles and as security mirrors in shops.

What is refraction and what are its laws? Why does light bend when it enters water?

Refraction is the bending of light when it travels from one medium to another with a different optical density. This happens because light changes speed at the interface of two media. The laws of refraction (Snell's Law) state that the incident ray, refracted ray, and normal at the point of incidence lie in the same plane, and that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for a given pair of media (n = sin i / sin r). When light travels from air (less dense) to water (more dense), it slows down and bends toward the normal. When it enters air from water, it speeds up and bends away from the normal. This is why a pencil half-dipped in water appears bent, why pools look shallower than they are, and why stars appear to twinkle.

How do convex and concave lenses form images? Explain using ray diagrams.

A convex lens (converging lens) is thicker at the centre and brings parallel rays of light to a point called the principal focus. The image formed depends on object position. If the object is beyond 2F, the image is real, inverted, and diminished (used in cameras). At 2F, the image is real, inverted, and same size. Between F and 2F, the image is real, inverted, and magnified (projectors). Within F, the image is virtual, erect, and magnified (magnifying glass). A concave lens (diverging lens) is thinner at the centre and always diverges light, forming a virtual, erect, and diminished image regardless of object position. Ray diagrams use three standard rays: one parallel to principal axis (refracts through focus), one through optical centre (goes straight), and one aimed at focus (emerges parallel). These diagrams help determine the nature and position of the image.

What are the mirror formula and lens formula and how are they used?

The mirror formula relates the object distance (u), image distance (v), and focal length (f) of a curved mirror: 1/v + 1/u = 1/f. The sign convention used is the New Cartesian Convention where distances measured in the direction of incident light are positive and against it are negative. The lens formula is similar: 1/v – 1/u = 1/f, where the same sign convention applies. Magnification for a mirror is m = –v/u and for a lens m = v/u. If magnification is positive, the image is erect; if negative, it is inverted. The power of a lens (P = 1/f, measured in dioptres) indicates how strongly it converges or diverges light. Positive power means converging (convex lens) and negative means diverging (concave lens). These formulas are crucial for solving numerical problems in Chapter 9.

NCERT Solutions for Class 10 Science Chapter 9 Light Reflection Refraction

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NCERT Solutions for Class 10 Science Chapter 9: Light — Reflection and Refraction

Light is all around us, and understanding how it behaves when it strikes different surfaces or passes through different media is what Chapter 9 of Class 10 Science is all about. NCERT Solutions for Class 10 Science Chapter 9 — Light: Reflection and Refraction are among the most sought-after resources during board exam preparation because this chapter is numerically heavy and conceptually rich.

Myclass24 provides complete, step-by-step solutions to every NCERT question in this chapter, covering the laws of reflection, mirror formula, ray diagrams for concave and convex mirrors, Snell's law of refraction, total internal reflection, and the lens formula. Students often find the mirror and lens formulas confusing, especially the sign convention. These solutions clarify every concept with easy examples and worked-out numericals. Whether you are studying for CBSE board exams, entrance tests, or your school assessments, these solutions are your most reliable companion for Chapter 9.

Download NCERT Solutions for Class 10 Science Chapter 9 Light — Reflection and Refraction PDF

The PDF of NCERT Solutions for Class 10 Science Chapter 9 — Light: Reflection and Refraction is available on Myclass24. It includes all numerical solutions with step-by-step working, ray diagrams, and important formulae. The PDF is formatted for mobile reading, making it easy to revise on the go. Download it free and use it for quick last-minute revision before exams.

Chapter 9: Light — Reflection and Refraction — Key Concepts, Facts & Topic Breakdown

Sign Convention (Cartesian)

All distances are measured from the pole (centre) of the mirror or optical centre of the lens
Distances measured in the direction of incident light are positive
Distances measured against the direction of incident light are negative
Heights above the principal axis are positive; heights below are negative

Important Formulae

Formula	Name	Symbols
1/v + 1/u = 1/f	Mirror Formula	v=image dist, u=object dist, f=focal length
m = -v/u = h'/h	Magnification (Mirror)	h'=image height, h=object height
1/v - 1/u = 1/f	Lens Formula	Same symbols, different sign convention
m = v/u = h'/h	Magnification (Lens)	Positive for virtual image in convex lens
n = sin i / sin r	Snell's Law	n=refractive index, i=angle of incidence, r=angle of refraction
n = c / v	Refractive Index	c=speed of light in vacuum, v=speed in medium

Image Formation by Concave Mirror

Object Position	Image Position	Nature of Image	Use
At infinity	At F	Real, inverted, highly diminished	—
Beyond C	Between F and C	Real, inverted, diminished	—
At C	At C	Real, inverted, same size	—
Between C and F	Beyond C	Real, inverted, enlarged	—
At F	At infinity	Real, inverted, highly enlarged	Searchlights
Between F and P	Behind mirror	Virtual, erect, enlarged	Shaving/make-up mirror

Image Formation by Convex Lens

Object Position	Image Position	Nature	Use
At infinity	At F2	Real, inverted, diminished	Camera
Beyond 2F1	Between F2 and 2F2	Real, inverted, diminished	Camera
At 2F1	At 2F2	Real, inverted, same size	—
Between F1 and 2F1	Beyond 2F2	Real, inverted, enlarged	Projector
At F1	At infinity	Real, inverted, highly enlarged	Searchlights
Between F1 and O	Same side as object	Virtual, erect, enlarged	Magnifying glass

Key Facts — Chapter 9

Speed of light in vacuum = 3 × 10⁸ m/s
Refractive index of glass ≈ 1.5; of water ≈ 1.33; of diamond ≈ 2.42
Total Internal Reflection occurs when light travels from denser to rarer medium and angle of incidence exceeds the critical angle — used in optical fibres
Power of lens = 1/f (in metres); unit is dioptre (D)
Convex mirror always forms virtual, erect, and diminished image — used in rear-view mirrors of vehicles
Concave mirror is a converging mirror; Convex mirror is a diverging mirror
Concave lens is a diverging lens; Convex lens is a converging lens