Light, Shadows and Reflection: 45 flashcards
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1. What is light?
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Light is a form of energy that lets us see objects and travels in straight lines called rays.
2. What is a shadow?
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A shadow is the dark region formed behind an opaque object when it blocks the path of light.
3. What happens to light when it hits a transparent object?
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Almost all light passes through, so no shadow is formed.
4. What happens to light when it hits a translucent object?
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Some light passes through, so a faint shadow is formed.
5. What happens to light when it hits an opaque object?
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Light is blocked completely, so a dark, clear shadow is formed.
6. How does the distance between the object and the light source affect shadow size?
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The closer the object is to the light source, the larger the shadow; the farther away, the smaller the shadow.
7. What kind of shadow does a point source of light give?
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A sharp, clear shadow.
8. What kind of shadow does an extended source of light give?
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A blurry shadow with a darker middle and lighter edges.
9. What is reflection?
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Reflection is the bouncing back of light from a surface.
10. What is regular reflection?
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Reflection from a smooth, polished surface like a mirror that produces a clear image.
11. What is diffuse reflection?
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Reflection from a rough surface that scatters light in many directions.
12. State the first law of reflection.
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The angle of incidence is always equal to the angle of reflection.
13. State the second law of reflection.
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The incident ray, the reflected ray, and the normal all lie in the same plane.
14. What is the normal?
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An imaginary line perpendicular to the reflecting surface at the point of incidence.
15. List the properties of an image formed by a plane mirror.
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It is virtual, erect, same size as the object, laterally inverted, and appears as far behind the mirror as the object is in front.
16. What is lateral inversion?
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The swapping of left and right in the image formed by a plane mirror.
17. What is a virtual image?
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An image that cannot be caught on a screen and only appears to be behind the mirror.
18. What are luminous objects?
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Objects that emit their own light, such as the Sun, a bulb, or a flame.
19. What are non-luminous objects?
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Objects that do not emit their own light but reflect light from other sources.
20. Why can we see the Moon?
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The Moon is non-luminous; it reflects sunlight, which reaches our eyes.
21. Why can we see ordinary objects like this page?
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Because they reflect light from a source into our eyes through diffuse reflection.
22. Name two devices that work on the principle of reflection.
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Solar cookers and periscopes.
23. What causes a solar eclipse?
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A solar eclipse occurs when the Moon's shadow falls on the Earth.
24. Why does a mirror form a clear image but a wall does not?
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A mirror has a smooth surface that reflects light in an organised way (regular reflection), while a wall has a rough surface that scatters light (diffuse reflection).
25. What is the difference between regular and diffuse reflection?
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Regular reflection occurs on smooth surfaces and forms clear images; diffuse reflection occurs on rough surfaces and scatters light in many directions.
26. Why do shadows have the same shape as the object casting them?
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Because light travels in straight lines and cannot bend around the opaque object.
27. What happens to the shadow if you move the torch farther from your hand?
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The shadow becomes smaller.
28. What happens to the shadow if you move the torch closer to your hand?
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The shadow becomes larger.
29. Give an example of a transparent material.
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Clear glass (or air).
30. Give an example of a translucent material.
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Frosted glass or butter paper.
31. Give an example of an opaque material.
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Wood, metal, or your hand.
32. What is the angle of incidence?
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The angle between the incident ray and the normal.
33. What is the angle of reflection?
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The angle between the reflected ray and the normal.
34. How far behind a plane mirror does the image appear?
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As far behind the mirror as the object is in front of it.
35. Is the image in a plane mirror erect or inverted?
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Erect (upright).
36. Is the image in a plane mirror real or virtual?
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Virtual — it cannot be caught on a screen.
37. What is the size of the image formed by a plane mirror compared to the object?
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The image is exactly the same size as the object.
38. How do periscopes use reflection?
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They use two mirrors to reflect light so that a person can see objects above the water surface.
39. How do solar cookers use reflection?
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They use mirrors to concentrate sunlight onto a cooking pot.
40. What is the role of the normal in reflection?
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It is a reference line perpendicular to the surface, used to measure the angles of incidence and reflection.
41. Why does a shadow form behind an opaque object?
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Because light travels in straight lines and cannot pass through the opaque object, leaving a dark region behind it.
42. What is the difference between a shadow and a reflection?
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A shadow is a dark region formed when light is blocked; a reflection is the bouncing back of light from a surface.
43. Why can't you see your face in a wall?
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Because the wall's rough surface causes diffuse reflection, scattering light in many directions instead of forming an organised image.
44. What type of reflection lets you see this page from any angle?
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Diffuse reflection.
45. What type of reflection forms a clear image in a mirror?
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Regular reflection.
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