Light — Class 8 Science NCERT Solutions (Free)
Free step-by-step NCERT solutions for Class 8 Science chapter "Light" — 8 important questions with detailed answers for CBSE board exam preparation.
TL;DR: Free step-by-step NCERT solutions for Class 8 Science chapter "Light" — 8 important questions with detailed answers for CBSE board exam preparation.
Written & reviewed by the Syllab.in Academic Team (CBSE/NCERT subject experts) · Updated
NCERT Solutions for Class 8 Science — Light. Step-by-step answers to all 8 textbook questions from this chapter, written for CBSE board preparation and free to use.
Light — All 8 Questions Solved
Q1. Define refraction of light. When does it occur?
Refraction is the bending of light when it passes from one transparent medium to another of different optical density. It occurs because light travels at different speeds in different media. Light bends toward the normal when entering a denser medium (water) and away from the normal when entering a rarer medium (air). The angle and amount of bending depend on the refractive indices.
Q2. A ray of light enters glass from air at 30° to the normal. The refracted ray bends by 10°. Find the angle of refraction.
Step 1: Angle of incidence (i) = 30°
Step 2: Light bends toward the normal when entering denser medium
Step 3: Angle of refraction (r) = 30° - 10° = 20°
Angle of refraction = 20°
Q3. What is dispersion of light? Explain with the example of a prism.
Dispersion is the splitting of white light into its component colours when passing through a prism. White light comprises seven colours (VIBGYOR). Different colours have different refractive indices in glass. Red (longer wavelength) bends least, violet (shorter wavelength) bends most. Prism separates these colours spatially, creating a spectrum. Newton proved white light is composite.
Q4. What is a lens? Name two types of lenses.
A lens is a transparent optical device made of glass or plastic with curved surfaces that refract light to form images. Two types: (1) Convex lens (converging)—thicker at center, converges light rays, forms real/virtual images depending on object distance, used in magnifying glasses and cameras. (2) Concave lens (diverging)—thinner at center, diverges light rays, forms virtual images, used in correction of myopia.
Q5. Why does a pencil in water appear to bend?
The pencil appears bent due to refraction of light. Light rays from the submerged part of the pencil refract (bend away from normal) when crossing the water-air boundary. This refraction changes the direction of light rays, making the underwater portion appear displaced and bent relative to the portion above water. Our eye perceives the light's path, not the actual position.
Q6. What is the power of a lens? Give the formula and its unit.
Power of a lens is its ability to converge or diverge light. Formula: P = 1/f, where f = focal length in meters. Unit: Dioptre (D). 1 D = 1/meter. Convex lenses have positive power (converging), concave lenses have negative power (diverging). A +2 D lens has focal length 0.5 m. Power increases as focal length decreases.
Q7. A convex lens has a focal length of 20 cm. Calculate its power.
Step 1: Convert focal length to meters: f = 20 cm = 0.2 m
Step 2: Power P = 1/f = 1/0.2 = 5 D
Power = +5 Dioptre (positive for convex lens)
Q8. How does a concave mirror form different types of images based on object position?
At different object distances from a concave mirror: (1) Beyond 2f: Real, inverted, diminished image. (2) At 2f: Real, inverted, same size. (3) Between f and 2f: Real, inverted, magnified. (4) At f: No image forms (rays are parallel). (5) Between mirror and f: Virtual, erect, magnified image. These properties depend on reflection and focal length of the mirror.
Light — Practice MCQs with Answers
Attempt these 20 multiple-choice questions after working through the solutions above. Each carries the correct option and the reasoning behind it, so a wrong answer tells you which idea to revisit.
MCQ 1. What is the relationship between the angle of incidence and the angle of reflection during reflection of light from a plane surface?
- A. Angle of incidence is greater than angle of reflection.
- B. Angle of incidence is smaller than angle of reflection.
- C. Angle of incidence is equal to angle of reflection.
- D. Angle of incidence and angle of reflection are always 90 degrees.
Answer: C. Angle of incidence is equal to angle of reflection. — According to the first law of reflection, the angle of incidence is always equal to the angle of reflection. This holds true for all types of regular reflection from a smooth surface.
MCQ 2. Which of the following characteristics is NOT true for an image formed by a plane mirror?
- A. It is virtual.
- B. It is inverted (upside down).
- C. It is erect.
- D. It is laterally inverted.
Answer: B. It is inverted (upside down). — An image formed by a plane mirror is always virtual, erect, and laterally inverted. It is never inverted (upside down) but rather side-wise inverted.
MCQ 3. Which of the following is an example of a luminous object?
- A. The Moon
- B. A chair
- C. A glowing bulb
- D. A book
Answer: C. A glowing bulb — Luminous objects are those that emit their own light. A glowing bulb produces light, whereas the Moon reflects light from the Sun, and a chair and a book do not produce light.
MCQ 4. Which part of the human eye controls the amount of light entering it?
- A. Cornea
- B. Retina
- C. Pupil
- D. Iris
Answer: D. Iris — The iris is a dark muscular diaphragm that controls the size of the pupil. By adjusting the pupil's size, the iris regulates the amount of light entering the eye, similar to the aperture of a camera.
MCQ 5. When white light passes through a prism, it splits into its seven constituent colours. This phenomenon is called:
- A. Reflection
- B. Refraction
- C. Dispersion
- D. Scattering
Answer: C. Dispersion — The phenomenon of splitting of white light into its constituent colours when it passes through a prism is known as dispersion of light. The band of colours formed is called the spectrum.
MCQ 6. Why does a highly polished surface produce a clear image, while a rough surface does not?
- A. Polished surfaces reflect more light.
- B. Rough surfaces absorb all light.
- C. Polished surfaces cause regular reflection, while rough surfaces cause diffuse reflection.
- D. Rough surfaces refract light in different directions.
Answer: C. Polished surfaces cause regular reflection, while rough surfaces cause diffuse reflection. — A highly polished surface causes regular reflection, where parallel rays of light remain parallel after reflection, forming a clear image. A rough surface causes diffuse reflection, scattering parallel rays in different directions, thus no clear image is formed.
MCQ 7. The ability of the eye to retain the image of an object for a short period even after the object is removed is known as:
- A. Accommodation
- B. Persistence of vision
- C. Far point
- D. Near point
Answer: B. Persistence of vision — Persistence of vision is the phenomenon where the image formed on the retina remains for about 1/16th of a second even after the object is no longer present. This principle is used in cinematography to create the illusion of continuous motion.
MCQ 8. Light generally travels in:
- A. Curved lines
- B. Zig-zag paths
- C. Straight lines
- D. Wavy paths
Answer: C. Straight lines — Light travels in straight lines. This property is known as the rectilinear propagation of light and can be observed in phenomena like shadow formation.
MCQ 9. The Braille system is a script developed for visually challenged people. Who developed this system?
- A. Louis Pasteur
- B. Louis Braille
- C. Alexander Graham Bell
- D. Isaac Newton
Answer: B. Louis Braille — The Braille system was developed by Louis Braille in 1821. It is a tactile system that allows visually challenged individuals to read and write through raised dots.
MCQ 10. Which of the following is the most critical precaution for maintaining good eye health?
- A. Washing eyes with water daily.
- B. Avoiding reading in dim light.
- C. Consuming Vitamin A rich foods.
- D. Not looking directly at very bright light sources like the Sun.
Answer: D. Not looking directly at very bright light sources like the Sun. — While all options are good for eye care, directly looking at intense light sources like the Sun can cause irreversible damage to the retina, making it the most critical precaution.
MCQ 11. A kaleidoscope works on the principle of:
- A. Single reflection
- B. Refraction
- C. Multiple reflections
- D. Dispersion of light
Answer: C. Multiple reflections — A kaleidoscope uses multiple mirrors placed at an angle to each other to create beautiful and symmetrical patterns through repeated reflections of objects placed inside it.
MCQ 12. If a light ray strikes a plane mirror at an angle of 30 degrees with the normal, what is the angle of incidence?
- A. 60 degrees
- B. 30 degrees
- C. 90 degrees
- D. 0 degrees
Answer: B. 30 degrees — The angle of incidence is defined as the angle between the incident ray and the normal to the surface at the point of incidence. In this case, it is directly given as 30 degrees.
MCQ 13. When you stand in front of a plane mirror, your right hand appears as your left hand in the image. This phenomenon is called:
- A. Vertical inversion
- B. Lateral inversion
- C. Regular reflection
- D. Diffuse reflection
Answer: B. Lateral inversion — Lateral inversion is the phenomenon where the left and right sides of an object appear to be interchanged in the image formed by a plane mirror.
MCQ 14. In the human eye, where is the image of an object formed?
- A. Cornea
- B. Iris
- C. Retina
- D. Optic nerve
Answer: C. Retina — The lens of the eye focuses light onto the retina, which is the light-sensitive screen at the back of the eye. The retina contains photoreceptor cells that convert light into electrical signals.
MCQ 15. What is the correct order of colours in a spectrum of white light, starting from the one that deviates the most when passing through a prism?
- A. Red, Orange, Yellow, Green, Blue, Indigo, Violet
- B. Violet, Indigo, Blue, Green, Yellow, Orange, Red
- C. Red, Violet, Blue, Green, Yellow, Orange, Indigo
- D. Violet, Green, Red, Blue, Indigo, Orange, Yellow
Answer: B. Violet, Indigo, Blue, Green, Yellow, Orange, Red — When white light disperses, violet light deviates the most and red light deviates the least. The correct order from most deviated to least deviated is VIBGYOR (Violet, Indigo, Blue, Green, Yellow, Orange, Red).
MCQ 16. A periscope uses two plane mirrors. How are these mirrors generally placed with respect to each other to allow viewing around corners?
- A. Parallel to each other
- B. Perpendicular to each other
- C. At 45 degrees to each other
- D. At 60 degrees to each other
Answer: A. Parallel to each other — In a simple periscope, two plane mirrors are placed parallel to each other, facing inwards, and typically at an angle of 45 degrees to the line of sight. This allows light to be reflected twice, enabling viewing over obstacles.
MCQ 17. The point on the retina where the optic nerve leaves the eye and there are no sensory cells is called the:
- A. Yellow spot
- B. Blind spot
- C. Fovea
- D. Pupil
Answer: B. Blind spot — The blind spot is a small area on the retina where the optic nerve connects and leaves the eye. Since there are no light-sensitive cells (rods and cones) at this point, any image falling on it cannot be seen.
MCQ 18. The bouncing back of light when it strikes a surface is called:
- A. Refraction
- B. Dispersion
- C. Reflection
- D. Absorption
Answer: C. Reflection — Reflection is the phenomenon where light rays return from a surface after striking it. It is one of the fundamental properties of light.
MCQ 19. An image formed by a plane mirror cannot be obtained on a screen. This means the image is:
- A. Real
- B. Inverted
- C. Virtual
- D. Enlarged
Answer: C. Virtual — A virtual image is an image that appears to be formed by the intersection of light rays but cannot actually be projected onto a screen. Images formed by plane mirrors are always virtual.
MCQ 20. Which type of cells in the retina are primarily responsible for vision in dim light and detecting motion?
- A. Cones
- B. Rods
- C. Iris cells
- D. Cornea cells
Answer: B. Rods — Rods are photoreceptor cells in the retina that are highly sensitive to dim light and are responsible for black-and-white vision and detecting motion. Cones are responsible for colour vision and vision in bright light.
How to Use These Solutions
Attempt each question yourself first and only then compare with the worked answer. Marks in the CBSE board exam are awarded for the METHOD as much as the final result, so reproduce the steps rather than memorising the last line. Where a solution states a law, a formula or a definition, learn that wording — examiners look for it.
Related practice for this chapter: chapter MCQs, previous-year questions, revision notes and sample papers.