Light: Shadows and Reflections – Short Answer Type Questions
CBSE Class 7 — Science
Chapter 11: Light: Shadows and Reflections — 50 Short Answer Questions & Answers (Topic-wise, NCERT-aligned)
Class 7
Science
NCERT
CBSE
Short Answers
Content Bank — Chapter 11 Overview
Concise short-answer practice covering: ray model of light, shadows (umbra & penumbra), factors affecting shadows, reflection and its laws, plane mirrors and image properties, periscopes and simple optical devices, experiments and common examples — strictly as per NCERT syllabus and suitable for CBSE Class 7 exam preparation.
50 Short Answer Questions — Topic-wise
Topic A — Nature of Light & Rays (Questions 1–8)
- 1. What is a light ray?A light ray is an imaginary straight line indicating the direction in which light travels; used in ray diagrams.
- 2. Define rectilinear propagation of light.Rectilinear propagation means light travels in straight lines in a homogeneous medium.
- 3. Describe a simple observation that shows light travels in straight lines.Pinhole experiment: light through a small hole projects a circular spot on a screen, showing straight-line travel.
- 4. What is meant by the path of light?The path of light is the route taken by light rays; drawn as straight lines in diagrams to show direction.
- 5. What is an incident ray?An incident ray is a ray that strikes a surface before reflection or refraction.
- 6. What is a reflected ray?A reflected ray is the ray that bounces off the surface after the incident ray strikes it.
- 7. Why do we use ray diagrams?Ray diagrams help predict and explain how light behaves—showing reflection, image formation and direction of rays clearly.
- 8. What is the normal line in reflection diagrams?The normal is an imaginary line perpendicular to the reflecting surface at the point of incidence, used to measure angles.
Topic B — Shadows (Questions 9–18)
- 9. What is a shadow?A shadow is a dark area formed on a surface when an opaque object blocks the light from a source.
- 10. Define umbra.Umbra is the darkest part of a shadow where the light source is completely blocked.
- 11. Define penumbra.Penumbra is the partially shaded region around the umbra where only part of the light is obstructed.
- 12. How does the size of the light source affect penumbra?A larger light source produces a larger penumbra, making the shadow edges less sharp.
- 13. How does moving the object closer to the screen affect the shadow size?Moving the object closer to the screen usually makes the shadow larger and sharper (depending on source size).
- 14. How does moving the light source closer to the object affect the shadow?Bringing the source closer typically increases shadow size and may increase fuzziness if the source is extended.
- 15. Why do we get multiple shadows when more than one light source is present?Each light source creates its own shadow (umbra and penumbra); multiple sources produce overlapping shadows.
- 16. What practical activity demonstrates shadow formation?Using a torch and an opaque object against a screen: vary distances to observe shadow size and sharpness changes.
- 17. Why are shadows sharp on a sunny day?Sun acts as a nearly point source at ground level, producing sharp shadows with small penumbra.
- 18. Give one everyday example of shadows affecting daily life.Shadows affect temperature and light in buildings; gardeners use shade to protect plants from intense sun.
Topic C — Reflection & Laws (Questions 19–30)
- 19. What is reflection of light?Reflection is the bouncing back of light from a surface when it cannot pass through.
- 20. Differentiate between regular and diffuse reflection.Regular reflection occurs on smooth surfaces producing clear images; diffuse reflection occurs on rough surfaces scattering light and producing no clear image.
- 21. State the first law of reflection.The incident ray, reflected ray and normal lie in the same plane.
- 22. State the second law of reflection.The angle of incidence equals the angle of reflection (measured from the normal).
- 23. Why is the normal important in measuring angles?The normal serves as the reference line from which incidence and reflection angles are measured accurately.
- 24. How does surface smoothness affect reflection?Smoother surfaces give regular reflection and clear images; rough surfaces scatter light causing diffuse reflection.
- 25. What is an example of regular reflection besides mirrors?Reflection from calm water can act like a mirror and show regular reflection.
- 26. How do ray diagrams illustrate the laws of reflection?Ray diagrams show incident and reflected rays with the normal; equal angles demonstrate the second law visually.
- 27. What happens to the direction of a ray after reflection on a plane surface?The ray leaves the surface at an angle equal to its angle of incidence, on the opposite side of the normal.
- 28. Why can we see ourselves in a polished mirror?Because regular reflection from the smooth mirror surface directs light from our face into our eyes forming an image.
- 29. Can white paper show regular reflection?No; white paper shows diffuse reflection scattering light, so it appears bright but does not form clear images.
- 30. How is angle of incidence measured?Angle of incidence is measured between the incident ray and the normal at the point of incidence.
Topic D — Plane Mirrors & Image Properties (Questions 31–40)
- 31. What is a plane mirror?A plane mirror is a flat reflecting surface that produces regular reflection and virtual images.
- 32. Describe a virtual image formed by a plane mirror.A virtual image appears behind the mirror where the reflected rays seem to meet; it cannot be projected on a screen.
- 33. Is the image in a plane mirror erect or inverted?The image is erect (upright), not inverted.
- 34. Explain lateral inversion with an example.Lateral inversion means left and right swap in the mirror; e.g., raise your left hand, the image appears to raise its right hand.
- 35. How does object distance relate to image distance in a plane mirror?Object distance from the mirror equals image distance behind the mirror for plane mirrors.
- 36. Can plane mirrors magnify objects?No, plane mirrors produce images of the same size as the object (no magnification).
- 37. What is a periscope and its basic principle?A periscope is an instrument using two plane mirrors at 45° to see over obstacles by reflecting light down into the viewer’s eye.
- 38. How do you locate an image in a plane mirror using ray tracing?Draw at least two incident rays from a point on the object, reflect them using equal angles, extend reflected rays backward to find their intersection—the image point.
- 39. Why does a plane mirror not form a real image?Because reflected rays diverge and do not actually meet; the image is formed by apparent intersection behind the mirror.
- 40. Give one use of a plane mirror in daily life.Uses include dressing mirrors, rear-view mirrors in vehicles (flat mirrors for close vision), and decorative mirrors.
Topic E — Applications, Practicals & Misc (Questions 41–50)
- 41. What practical experiment can show the laws of reflection?Using a plane mirror, protractor and a ray of light (or laser pointer) to measure and compare angles of incidence and reflection proves the laws.
- 42. How does a kaleidoscope use reflection?A kaleidoscope uses several mirrors at angles to produce multiple repeated images by successive reflections.
- 43. Why are polished metal surfaces reflective?Polished metals have smooth surfaces that cause regular reflection, producing clear reflections.
- 44. How does reflection help in periscopes used in submarines?Mirrors redirect light so someone inside can view the surface from a submerged position without direct line-of-sight.
- 45. Mention a safety application of mirrors.Convex mirrors on roads and in stores provide wide-angle views for safety and surveillance (not in NCERT core but common application).
- 46. What is the effect of surface scratches on a mirror?Scratches make reflection less regular, scattering light and reducing image clarity.
- 47. Describe how to perform the pinhole experiment.Make a small hole in a card, allow light to pass and project onto a screen; the spot demonstrates straight-line propagation of light.
- 48. How does increasing the distance between screen and object affect shadow sharpness for a point source?For a near point source, moving the screen away makes the shadow larger but may remain relatively sharp if source is small.
- 49. Why are classroom demonstrations important for this chapter?Hands-on demonstrations reinforce understanding of abstract ideas (rays, reflection, shadows) and help students visualise concepts.
- 50. Give one exam tip for answering optics questions in Class 7.Always draw neat, labelled ray diagrams with normal lines and clearly marked angles—diagrams earn marks and clarify reasoning.
Prepared strictly as per NCERT Class 7 Chapter 11 — suitable for quick revision, classroom handouts and CBSE exam practice.