Chapter 11: Light: Shadows and Reflections
Why does the Moon shine, why are shadows dark, and why is AMBULANCE written backwards? In this chapter we sort luminous and non-luminous objects, show that light travels in straight lines, test transparent, translucent and opaque materials, play with shadows, explore mirror images and lateral inversion, and build a pinhole camera, periscope and kaleidoscope.
In this chapter you will
- tell luminous from non-luminous objects
- show that light travels in straight lines and explain shadows
- describe images in a plane mirror
- explain the pinhole camera, periscope and kaleidoscope
Topics
- Sources of Light and How It Travels NCERT 11.1–11.3
Luminous objects give out their own light; the Moon only reflects sunlight.
- Shadow Formation NCERT 11.4
A shadow forms where an opaque object blocks light; you need a source, an object and a screen.
- Reflection and Mirror Images NCERT 11.5–11.6
Reflection is the change in direction of light at a mirror or shiny surface.
- Pinhole Camera, Periscope and Kaleidoscope NCERT 11.7–11.8
A pinhole camera forms an upside-down image because light travels in straight lines.
Key words
- Luminous
- gives out its own light
- Translucent
- lets some light through
- Opaque
- blocks light completely
- Shadow
- dark region where an object blocks light
- Reflection
- change in direction of light at a mirror
- Lateral inversion
- left–right swap in a mirror image
- Pinhole camera
- box with a tiny hole giving an inverted image
Summary
- Luminous objects make light; the Moon reflects sunlight; light travels in straight lines.
- Transparent, translucent and opaque materials pass all, some or no light.
- Shadows need a source, an opaque object and a screen; their size depends on positions.
- Plane mirror images are erect, same size and laterally inverted; a pinhole camera's image is inverted.