50 Very Short Answer Questions — Chapter 11: Light: Shadows and Reflections

1. 1. What is a light ray? — A straight line showing the path of light.
2. 2. Define rectilinear propagation. — Light travels in straight lines in a uniform medium.
3. 3. What is a shadow? — A dark region formed when an opaque object blocks light.
4. 4. What is umbra? — The fully dark inner part of a shadow where all light is blocked.
5. 5. What is penumbra? — The partially shaded outer region of a shadow receiving some light.
6. 6. How does the size of a light source affect shadow sharpness? — Larger sources create fuzzier shadows (larger penumbra); point sources give sharp shadows.
7. 7. Name two factors that affect shadow size. — Distances between source-object and object-screen (and source size).
8. 8. Why do multiple shadows form? — Because of multiple light sources producing separate shadows.
9. 9. What is reflection of light? — The bouncing back of light from a surface.
10. 10. Give one example of regular reflection. — Reflection from a plane mirror.
11. 11. Give one example of diffuse reflection. — Light reflected from paper or cloth.
12. 12. State the first law of reflection. — Incident ray, reflected ray and normal lie in the same plane.
13. 13. State the second law of reflection. — Angle of incidence equals angle of reflection.
14. 14. What is the normal in reflection? — A line perpendicular to the surface at the point of incidence.
15. 15. What is a plane mirror? — A flat reflecting surface that produces regular reflection.
16. 16. Describe a virtual image. — An image from which light appears to come but cannot be projected on a screen.
17. 17. Are images in plane mirrors real or virtual? — Virtual.
18. 18. State one property of an image in a plane mirror. — Image is same size as the object.
19. 19. What does laterally inverted mean? — Left and right appear swapped in a mirror image.
20. 20. How far behind a plane mirror is the image located compared to the object distance? — At the same distance behind the mirror as the object is in front.
21. 21. Why can’t a virtual image be caught on a screen? — Because light rays do not actually meet at the image point; they only appear to diverge from it.
22. 22. What is a periscope used for? — To see over or around obstacles, often in submarines or trenches.
23. 23. How many mirrors are used in a simple periscope? — Two plane mirrors, each at 45°.
24. 24. What happens to a ray that strikes a smooth mirror? — It reflects at an angle equal to its angle of incidence.
25. 25. Define diffuse reflection in one line. — Reflection from rough surfaces scattering light in many directions.
26. 26. Why do we see non-shiny objects? — Because they reflect light diffusely into our eyes.
27. 27. What is the purpose of the normal line in drawing ray diagrams? — To measure and compare incidence and reflection angles accurately.
28. 28. What is meant by the path of light? — The direction along which light travels, often shown by rays.
29. 29. How does moving the object closer to the light source affect its shadow on a screen? — The shadow becomes larger and less sharp (if source size not negligible).
30. 30. Name a household use of plane mirrors. — Dressing mirror or bathroom mirror.
31. 31. What is meant by the term 'incident ray'? — The incoming ray that strikes a surface.
32. 32. What is 'reflected ray'? — The ray that bounces off a surface after incidence.
33. 33. Can a plane mirror produce a magnified image? — No; plane mirrors produce images of the same size.
34. 34. What causes penumbra? — Partial obstruction of an extended light source causes penumbra.
35. 35. How does increasing distance between object and screen change the shadow? — Shadow size decreases as object moves farther from the screen (for fixed source-object distance).
36. 36. Name an optical device that uses reflection. — Periscope, mirror, kaleidoscope.
37. 37. How are images in a plane mirror formed with respect to rays? — By extending reflected rays backwards; their intersection locates the virtual image.
38. 38. What is lateral inversion observable in mirrors? — Your right hand appears as left in the mirror image.
39. 39. Why are polished surfaces used as mirrors? — They give regular reflection, forming clear images.
40. 40. What is a pinhole experiment used to show? — Straight-line propagation of light.
41. 41. Why do shadows appear pale sometimes? — Due to penumbra where some light reaches, making the edge lighter.
42. 42. Give one reason why periscopes have mirrors at 45°. — To reflect light at right angles so the line of sight is redirected upward or downward.
43. 43. What is the effect of a rough surface on image formation? — No clear image is formed due to scattering (diffuse reflection).
44. 44. Can a plane mirror form a real image? — No, plane mirrors only form virtual images.
45. 45. Mention one safety use of mirrors. — Rear-view mirrors in vehicles for safer driving.
46. 46. What does the size of an image in a plane mirror depend on? — Only on the object's size and distance; it remains equal to object size for plane mirrors.
47. 47. What is meant by 'apparent depth' in reflection context? — How deep an object appears due to optical effects (not central in this chapter but related to perception).
48. 48. How does having two identical light sources affect the shadow? — Two overlapping shadows are formed, each corresponding to a source.
49. 49. Why do we use mirrors in periscopes instead of lenses? — Because periscopes redirect light via reflection and require simple geometric redirection rather than refraction.
50. 50. Why is it important to draw a normal while making ray diagrams? — The normal provides the reference to measure and equalize incident and reflected angles per the laws of reflection.

Prepared according to NCERT Class 7 Chapter 11: Light: Shadows and Reflections — ideal for quick revision, classroom handouts and CBSE exam prep.