NCERT Solutions for CBSE Class 8 Science Chapter 13: Light

The laws of reflection form the foundation of CBSE Class 8 Science Chapter 13 Light and appear in nearly every Class 8 term examination. The first law states that the incident ray, reflected ray, and the normal to the mirror at the point of incidence all lie in the same plane. The second law states that the angle of incidence is equal to the angle of reflection. A critical point that trips up 40% of students: these angles are always measured from the normal (the perpendicular line to the mirror surface), never from the mirror itself. If a ray strikes a plane mirror at 30° to the normal, it reflects at 30° on the opposite side of the normal. Many NCERT questions in Class 8 Science Chapter 13 ask students to draw accurate ray diagrams showing incident ray, point of incidence, normal, angle markings, and reflected ray. Examiners award 1 mark for correct diagram construction and 1 mark for stating the laws precisely. Regular practice of these diagrams using a ruler, protractor, and sharp pencil is essential for scoring full marks in practical-based questions that constitute 3–4 marks in the chapter.

NCERT Class 8 Science clearly distinguishes between regular (specular) reflection and diffused (irregular) reflection, a 3-mark question favourite in CBSE exams. Regular reflection occurs when parallel rays of light strike a smooth, polished surface like a plane mirror, still water, or polished metal. All reflected rays emerge parallel to each other, forming clear images. This is why you see a sharp reflection of your face in a mirror. Diffused reflection happens when parallel incident rays strike a rough or irregular surface such as paper, cloth, cardboard, or a plastered wall. Each point on the rough surface has a different orientation, so the reflected rays scatter in various directions. Importantly, the laws of reflection still apply at each individual point, but the overall effect is scattered light with no clear image formation. This is why you cannot see your reflection on a white painted wall even though light reflects from it. Understanding this distinction helps explain why we see most objects around us: they reflect light diffusely into our eyes. CBSE Class 8 Science Chapter 13 Light exam questions often ask students to draw two diagrams side-by-side comparing these reflection types and explain why a cinema screen uses diffused reflection to ensure every viewer sees the image regardless of their seating position.

Multiple reflections occur when light reflects off two or more mirrors, creating fascinating effects explored in CBSE Class 8 Science Chapter 13 Light through kaleidoscopes and periscopes. In a kaleidoscope, three plane mirrors are arranged at 60° to each other in a triangular tube. Coloured glass pieces at one end undergo multiple reflections, creating beautiful symmetrical patterns. The number of images formed when two plane mirrors are placed at an angle θ is given by the formula (360°/θ) − 1, provided this yields a whole number. For instance, at 60°, you get (360°/60°) − 1 = 5 images. At 90°, you get 3 images. This formula appears in roughly 25% of Class 8 Science term papers as a 2-mark numerical question. Periscopes use two plane mirrors arranged parallel to each other at 45° to allow submarine crews or people in crowded places to see over obstacles. Light from the object strikes the top mirror at 45°, reflects down the tube, strikes the bottom mirror at 45°, and reflects horizontally into the observer's eye. NCERT questions in Class 8 Science Chapter 13 ask students to draw neat labelled diagrams of both devices and explain the path of light through them, typically worth 3–5 marks in term exams.

Dispersion is the splitting of white light into its constituent seven colours when passing through a transparent medium like a glass prism — a concept thoroughly covered in CBSE Class 8 Science Chapter 13 Light. When white sunlight enters one face of a triangular prism, it refracts (bends) at the air-glass boundary. Different colours have different wavelengths and thus refract by different amounts. Violet light has the shortest wavelength and bends the most, while red light has the longest wavelength and bends the least. This separation creates the visible spectrum: Violet, Indigo, Blue, Green, Yellow, Orange, Red (VIBGYOR). The phenomenon occurs because the refractive index of glass varies slightly with wavelength. Newton demonstrated this using a prism in 1666, and NCERT Class 8 Science includes his historic experiment as a key concept. If you place a second identical prism inverted next to the first, the dispersed colours recombine into white light, proving that white light is a mixture of seven colours. This 'recombination experiment' appears in 15% of CBSE Class 8 term papers as a 3-mark diagram-based question. Understanding dispersion explains natural phenomena like rainbows, which form when sunlight disperses through millions of water droplets acting as tiny prisms.

Rainbow formation beautifully demonstrates dispersion and reflection principles taught in CBSE Class 8 Science Chapter 13 Light. A rainbow appears when sunlight interacts with water droplets suspended in the atmosphere after rain. Each droplet acts as a tiny prism. Sunlight enters the droplet, disperses into seven colours, reflects off the inner back surface of the droplet, and exits after refracting again. The observer sees different colours coming from different droplets at specific angles. Red light exits at approximately 42° from the antisolar point (the point opposite the sun), while violet exits at about 40°. This is why red forms the outer arc of the primary rainbow and violet the inner arc. Sometimes a secondary rainbow appears outside the primary one, with colours reversed, caused by two internal reflections inside the droplets. CBSE Class 8 Science Chapter 13 typically includes a 3–4 mark question asking students to explain rainbow formation with a labelled diagram showing sunlight entering a water droplet, undergoing dispersion, internal reflection, and emerging as separated colours. Students must mention that the observer must have their back to the sun to see the rainbow — a common exam trap question.

The human eye is a remarkable optical instrument thoroughly examined in CBSE Class 8 Science Chapter 13 Light, typically worth 5 marks in term exams through labelled diagrams and function-based questions. The outermost transparent layer is the cornea, which protects the eye and does most of the light refraction due to its curved shape. Behind the cornea is the anterior chamber filled with aqueous humour. The coloured iris controls the size of the pupil (the central opening) to regulate the amount of light entering the eye — dilating in dim light and constricting in bright light. The crystalline lens, held by ciliary muscles, is a transparent biconvex structure that fine-tunes focus by changing its curvature (a process called accommodation). Light passes through the vitreous humour (a transparent jelly filling the eyeball) and focuses on the retina, the light-sensitive inner lining containing photoreceptor cells. Rod cells detect light intensity and enable vision in dim conditions, while cone cells detect colour and work best in bright light. The optic nerve transmits electrical signals from the retina to the brain, which interprets them as images. The blind spot, where the optic nerve exits, contains no photoreceptors. NCERT Class 8 Science Chapter 13 includes a well-labelled diagram of the eye that students must memorize and be able to draw accurately for 3 marks in exams.

Accommodation is the ability of the eye to focus on objects at varying distances by changing the curvature of the lens — a vital concept in CBSE Class 8 Science Chapter 13 Light. When viewing distant objects, the ciliary muscles relax, the lens becomes thinner (less curved), and its focal length increases, allowing parallel rays from distant objects to focus on the retina. When viewing nearby objects, ciliary muscles contract, the lens becomes thicker (more curved), and its focal length decreases, converging the diverging rays from near objects onto the retina. The nearest point at which the eye can see objects clearly is called the near point or least distance of distinct vision, which is 25 cm for a normal healthy adult eye. The farthest point up to which the eye can see clearly is the far point, which is infinity for a normal eye. As people age, the ciliary muscles weaken and the lens loses flexibility, reducing the eye's accommodation power — a condition called presbyopia, requiring bifocal lenses. NCERT questions in Class 8 Science Chapter 13 often ask students to explain why we cannot see objects clearly when they are too close (less than 25 cm) or why elderly people struggle with near vision, typically worth 2–3 marks. Understanding accommodation is essential before studying vision defects.

Myopia, or short-sightedness, is the most frequently tested vision defect in CBSE Class 8 Science Chapter 13 Light, appearing in 60% of term papers as a 4–5 mark question with ray diagrams. A myopic person can see nearby objects clearly but cannot see distant objects sharply because the image of distant objects forms in front of the retina instead of on it. This occurs due to two possible causes: the eyeball is too long (elongated) from front to back, or the lens has excessive curvature, causing too much convergence of light rays. The far point of a myopic eye is not at infinity but at some finite distance closer to the eye. Myopia is corrected using a concave lens (diverging lens) of appropriate power placed in front of the eye. The concave lens diverges the incoming parallel rays slightly before they enter the eye, allowing the eye lens to focus them correctly on the retina. The power of the corrective concave lens must be calculated so that it shifts the far point to infinity. NCERT Class 8 Science Chapter 13 includes a ray diagram showing parallel rays from a distant object converging in front of the retina in a myopic eye, then a second diagram showing how a concave lens corrects this by diverging rays. Students must practice drawing both diagrams with correct ray paths, lens shapes, and labelling for full marks.

Hypermetropia, or long-sightedness, is the second major vision defect covered in CBSE Class 8 Science Chapter 13 Light, often paired with myopia in comparative 5-mark questions. A hypermetropic person can see distant objects clearly but cannot see nearby objects sharply because the image of near objects forms behind the retina instead of on it. This defect arises when the eyeball is too short from front to back, or the lens has insufficient curvature (too flat), causing inadequate convergence of light rays from near objects. The near point of a hypermetropic eye is farther than the normal 25 cm — perhaps 50 cm, 1 metre, or more, making reading and close work difficult. Hypermetropia is corrected using a convex lens (converging lens) of appropriate power placed in front of the eye. The convex lens provides additional convergence to the diverging rays from near objects before they enter the eye, allowing the eye lens to focus them onto the retina. The power of the corrective convex lens is chosen to shift the near point back to 25 cm. NCERT Class 8 Science Chapter 13 requires students to draw ray diagrams showing diverging rays from a near object failing to converge onto the retina in a hypermetropic eye (forming image behind retina), and a second diagram showing correction with a convex lens. This topic is especially relevant for elderly people experiencing presbyopia, a type of hypermetropia caused by age-related lens rigidity.

The NCERT textbook for CBSE Class 8 Science Chapter 13 Light contains approximately 12–15 end-of-chapter questions ranging from 1-mark objective questions to 5-mark long-answer questions requiring diagrams. These exercises test reflection laws, image formation in plane mirrors, the mirror formula for Class 8 level (qualitative), characteristics of images formed by plane mirrors (virtual, upright, same size, laterally inverted, at same distance behind mirror as object in front), multiple reflections in kaleidoscope and periscope, dispersion through prism with VIBGYOR sequence, structure and function of eye parts, differences between rods and cones, myopia and hypermetropia causes, symptoms, and corrections with appropriate diagrams, and real-life applications like why we use concave lenses for myopia. High-scoring students follow a structured approach: read the question carefully, underline keywords (e.g. 'with diagram', 'list differences', 'explain with reason'), allocate time per mark (roughly 1.5 minutes per mark), draw diagrams in pencil with ruler for straight lines, label all parts clearly, and write explanations in points rather than long paragraphs for clarity. CBSETUTOR.ai offers step-by-step solutions to every NCERT question in CBSE Class 8 Science Chapter 13 Light, allowing students to photograph any problem from their textbook and receive instant, curriculum-accurate answers explained in simple language, available 24×7 at a flat ₹999/month for complete access to Classes 6–12 across all subjects.

Students lose 30–40% of marks in CBSE Class 8 Science Chapter 13 Light due to avoidable errors that examiners flag year after year. The most frequent mistake is measuring angles of incidence and reflection from the mirror surface instead of the normal, leading to incorrect numerical answers. Another common error is confusing the corrective lenses: writing concave lens for hypermetropia or convex lens for myopia. Students often draw ray diagrams without using a ruler, resulting in wobbly lines and lost presentation marks (0.5–1 mark per diagram). Many forget to label diagrams completely — omitting critical labels like 'normal', 'angle of incidence', 'retina', or 'concave lens' costs 0.5 marks per missing label. In dispersion questions, students mix up the VIBGYOR sequence or incorrectly state that violet bends least (it actually bends most). When explaining diffused reflection, some students wrongly claim the laws of reflection do not apply to rough surfaces, when in fact they apply at each microscopic point. In human eye questions, confusing rods with cones (rods detect intensity/dim light, cones detect colour/bright light) is a typical mistake. During exam revision, create a checklist of these common errors, review marked answer scripts from previous tests, and practice timed diagram-drawing to improve speed and accuracy.

Scoring 9+ out of 10 marks in CBSE Class 8 Science Chapter 13 Light requires a systematic preparation strategy combining concept clarity, diagram practice, and timed problem-solving. Start by reading the NCERT textbook chapter thoroughly, highlighting key terms like 'regular reflection', 'dispersion', 'accommodation', 'myopia', and 'hypermetropia'. Create a separate notebook for diagrams and practice drawing each figure at least five times: laws of reflection with angle markings, kaleidoscope with three mirrors at 60°, periscope with two mirrors at 45°, dispersion through prism showing VIBGYOR, detailed human eye with all parts labelled, myopic eye with concave lens correction, and hypermetropic eye with convex lens correction. Use NCERT exemplar problems for additional practice beyond textbook exercises. Solve previous five years' CBSE Class 8 term exam papers under timed conditions (1.5 minutes per mark) to build speed. Make a formula and key points sheet: laws of reflection, number of images formula (360°/θ − 1), near point = 25 cm, far point = infinity for normal eye, myopia correction = concave lens, hypermetropia correction = convex lens. Revise this sheet daily in the week before exams. Form a study group to explain concepts to peers — teaching solidifies understanding. For any doubts during practice, parents can give their child access to CBSETUOR.ai, where the 24×7 AI tutor provides instant clarifications on every NCERT topic in CBSE Class 8 Science Chapter 13 Light, with the added benefit of covering all subjects from Classes 6–12 at one flat price of ₹999/month with a 3-day free trial requiring no credit card.

Parents across India are discovering that CBSETUTOR.ai transforms how students master CBSE Class 8 Science Chapter 13 Light by providing a personal AI tutor available 24×7 at a fraction of traditional tuition costs. The platform has ingested every NCERT textbook for Classes 6–12, ensuring every explanation aligns precisely with the CBSE curriculum. When a Class 8 student struggles with drawing the ray diagram for a concave lens correcting myopia, they simply photograph the question from their textbook or worksheet and upload it to CBSETUTOR.ai. Within seconds, the AI tutor provides a step-by-step solution with a properly labelled diagram, explains why the lens must be concave (diverging), shows the ray paths before and after correction, and even offers similar practice questions to reinforce the concept. This immediate feedback loop eliminates the frustration of waiting for the next tuition class or parent's availability. For conceptual doubts like 'Why does violet bend more than red in a prism?', students can ask in plain English and receive clear explanations about wavelength, refractive index variation, and dispersion — all grounded in NCERT terminology. The platform costs just ₹999 per month for complete access to all subjects and all classes from 6 to 12, with a 3-day free trial that requires no credit card, making it accessible to families across India who want quality education support without the ₹5,000–₹15,000 monthly burden of traditional tuitions.