Light — Class 7 Science NCERT Solutions (Free)
Free step-by-step NCERT solutions for Class 7 Science chapter "Light" — 8 important questions with detailed answers for CBSE board exam preparation.
TL;DR: Free step-by-step NCERT solutions for Class 7 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 7 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 light. How does it travel?
Light: form of energy that enables us to see objects. It is electromagnetic radiation visible to human eye (wavelength 380-700 nm). Light travels in straight lines (rectilinear propagation) with speed 3 × 10⁸ m/s in vacuum. Speed of light = c = 3 × 10⁸ m/s. Light travels slower in other media (water, glass) than in vacuum.
Q2. What are plane mirrors? Explain the laws of reflection.
Plane mirror: flat, smooth reflective surface. Laws of reflection:
1. Angle of incidence = Angle of reflection (both measured from normal)
2. Incident ray, reflected ray, and normal all lie in same plane
3. Rays reflect on smooth surfaces following these laws
Image in plane mirror: virtual, erect, same size as object, laterally inverted, same distance behind mirror as object is in front.
Q3. What is the difference between reflection and refraction?
Reflection: light bounces back from surface following laws of reflection; occurs at surface; angle of incidence = angle of reflection; no change in speed.
Refraction: light bends when entering different medium; occurs at interface; bends toward/away from normal depending on density; speed changes. Pencil in water appears bent due to refraction.
Reflection in mirrors; Refraction in lenses and transparent materials.
Q4. What is a lens? Explain convex and concave lenses.
Lens: transparent object made of glass/plastic with curved surfaces that refract light.
Convex lens: bulges outward; converges parallel rays at focal point (F); real, inverted, magnified image for objects closer than 2F; magnifying glass, camera, projector.
Concave lens: curves inward; diverges parallel rays; always produces virtual, erect, diminished image; used in spectacles for myopia (short-sightedness).
Focal length (f) = distance from lens to focal point.
Q5. Define angle of incidence and angle of refraction.
Angle of incidence (i): angle between incident ray and normal (perpendicular to surface) at point of incidence.
Angle of refraction (r): angle between refracted ray and normal.
Angle of reflection (for mirrors): angle between reflected ray and normal = angle of incidence.
Normal: imaginary line perpendicular to surface at point of contact.
Note: All angles measured from normal, not from surface itself.
Q6. What are the properties of light reflected by a plane mirror?
Properties of image in plane mirror:
1. Virtual: image cannot be caught on screen
2. Erect: image upright, same orientation as object
3. Same size: height of image = height of object
4. Laterally inverted: left and right reversed (write 'PAN' in front of mirror, image appears as backwards 'NAP')
5. Same distance: image distance behind mirror = object distance in front
6. Same light paths: light reflects following laws of reflection
Q7. How does a concave mirror form images? Explain with examples.
Concave mirror: converging mirror (curves inward like bowl). Images formed depend on object position:
1. Object beyond 2F: real, inverted, smaller image at F to 2F (camera)
2. Object at 2F: real, inverted, same size at 2F
3. Object between F and 2F: real, inverted, magnified beyond 2F (projector)
4. Object between F and mirror: virtual, erect, magnified (magnifying glass for shaving)
Focal point (F): point where parallel rays converge after reflection.
Q8. What is the human eye? Explain how it works.
Human eye: optical instrument for vision. Structure: Cornea (light entry), Iris (controls light), Lens (focuses light), Retina (light sensitive layer with photoreceptors), Optic nerve (transmits signal to brain).
Working: Light enters cornea, passes through pupil (iris opening), lens focuses light on retina, photoreceptors (rods and cones) detect light and convert to electrical signals, optic nerve sends signals to brain, brain processes signals to form image.
Defects: Myopia (nearsightedness-concave lens), Hyperopia (farsightedness-convex lens), Astigmatism (corrected spectacles).
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 describes the path of light?
- A. Curved line
- B. Straight line
- C. Zig-zag line
- D. Circular path
Answer: B. Straight line — Light always travels in a straight line, which is known as the rectilinear propagation of light.
MCQ 2. The bouncing back of light from a surface is called:
- A. Refraction
- B. Reflection
- C. Dispersion
- D. Absorption
Answer: B. Reflection — Reflection is the phenomenon where light rays bounce back after striking a surface.
MCQ 3. Which of the following is NOT a characteristic of the image formed by a plane mirror?
- A. Virtual
- B. Erect
- C. Real
- D. Laterally inverted
Answer: C. Real — The image formed by a plane mirror is always virtual, erect, of the same size as the object, and laterally inverted. Real images can be formed on a screen.
MCQ 4. Which of the following is a luminous object?
- A. Moon
- B. Chair
- C. Sun
- D. Book
Answer: C. Sun — Luminous objects are those that emit their own light, like the Sun, while non-luminous objects reflect light from other sources.
MCQ 5. Which type of mirror is used by dentists to see enlarged images of teeth?
- A. Plane mirror
- B. Convex mirror
- C. Concave mirror
- D. Cylindrical mirror
Answer: C. Concave mirror — Concave mirrors can form enlarged and erect images when the object is placed close to the mirror, making them suitable for dentists.
MCQ 6. Which type of mirror is commonly used as a rearview mirror in vehicles?
- A. Plane mirror
- B. Convex mirror
- C. Concave mirror
- D. Parabolic mirror
Answer: B. Convex mirror — Convex mirrors form virtual, erect, and diminished images, providing a wider field of view, which is essential for rearview mirrors in vehicles.
MCQ 7. If you stand 2 meters in front of a plane mirror, what is the distance between you and your image?
- A. 2 meters
- B. 1 meter
- C. 4 meters
- D. 0 meters
Answer: C. 4 meters — In a plane mirror, the image is formed as far behind the mirror as the object is in front of it. So, if you are 2m in front, your image is 2m behind, making the total distance 2m + 2m = 4m.
MCQ 8. The splitting of white light into its seven constituent colours is known as:
- A. Reflection
- B. Refraction
- C. Dispersion
- D. Diffraction
Answer: C. Dispersion — Dispersion is the phenomenon where white light splits into its constituent colours (VIBGYOR) when passed through a prism or water droplets.
MCQ 9. What is the correct order of colours in a spectrum of white light, from shortest to longest wavelength?
- A. Red, Orange, Yellow, Green, Blue, Indigo, Violet
- B. Violet, Indigo, Blue, Green, Yellow, Orange, Red
- C. Green, Yellow, Blue, Red, Orange, Violet, Indigo
- D. Yellow, Orange, Red, Violet, Indigo, Blue, Green
Answer: B. Violet, Indigo, Blue, Green, Yellow, Orange, Red — The spectrum of white light consists of seven colours, commonly remembered by the acronym VIBGYOR, which lists them in order from violet (shortest wavelength) to red (longest wavelength).
MCQ 10. Which optical device is used to split white light into its constituent colours?
- A. Lens
- B. Mirror
- C. Prism
- D. Filter
Answer: C. Prism — A prism is a transparent optical element with flat, polished surfaces that refract light and disperse it into its spectrum.
MCQ 11. A concave lens is also known as a:
- A. Converging lens
- B. Diverging lens
- C. Magnifying lens
- D. Plano-convex lens
Answer: B. Diverging lens — A concave lens is a diverging lens because it spreads out (diverges) parallel rays of light that pass through it.
MCQ 12. A convex lens is also known as a:
- A. Diverging lens
- B. Magnifying lens
- C. Converging lens
- D. Concavo-convex lens
Answer: C. Converging lens — A convex lens is a converging lens because it brings parallel rays of light to a focus (converges them) after passing through it.
MCQ 13. What kind of image is formed by a pinhole camera?
- A. Erect and magnified
- B. Inverted and real
- C. Virtual and erect
- D. Erect and real
Answer: B. Inverted and real — A pinhole camera forms an inverted and real image. It is real because it can be formed on a screen, and inverted due to the rectilinear propagation of light.
MCQ 14. Shiny surfaces like polished metal reflect light __________ than dull surfaces.
- A. Less
- B. More
- C. Similarly
- D. Inversely
Answer: B. More — Highly polished and shiny surfaces are good reflectors of light and reflect most of the light falling on them, unlike dull or rough surfaces.
MCQ 15. Shadows are formed because:
- A. Light bends around objects.
- B. Light is absorbed by objects.
- C. Light travels in a straight line and objects block its path.
- D. Objects emit light.
Answer: C. Light travels in a straight line and objects block its path. — Shadows are formed when an opaque object blocks the path of light, demonstrating that light travels in straight lines and cannot pass through opaque objects.
MCQ 16. If you raise your right hand in front of a plane mirror, your image appears to raise its:
- A. Right hand
- B. Left hand
- C. Both hands
- D. Neither hand
Answer: B. Left hand — A plane mirror exhibits lateral inversion, meaning that the right side of the object appears as the left side of the image, and vice versa.
MCQ 17. Which of the following can form a real image?
- A. Plane mirror
- B. Convex mirror
- C. Concave mirror
- D. Concave lens
Answer: C. Concave mirror — Among the given options, only a concave mirror can form a real image, provided the object is placed beyond its focal point.
MCQ 18. Which type of lens can form both real and virtual images depending on the object's position?
- A. Concave lens
- B. Convex lens
- C. Cylindrical lens
- D. Plano-concave lens
Answer: B. Convex lens — A convex lens can form real and inverted images when the object is placed beyond its focal point, and virtual, erect, and magnified images when the object is placed between the optical centre and the focal point.
MCQ 19. Which travels fastest?
- A. Sound
- B. Light
- C. Water waves
- D. Wind
Answer: B. Light — Light travels at the fastest speed known in the universe, approximately 3 x 10^8 meters per second in a vacuum.
MCQ 20. The lens in the human eye is a type of:
- A. Concave lens
- B. Convex lens
- C. Cylindrical lens
- D. Plano lens
Answer: B. Convex lens — The natural lens in the human eye is a convex lens, which converges light rays to form a real, inverted image on the retina.
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.