Sources of Light
Light is a form of energy that enables us to see things around us. When light from an object enters our eyes, we are able to see it.
Luminous Objects: Objects that emit their own light are called luminous objects. Examples: Sun, Stars, Fire, Electric Bulb.
Non-Luminous Objects: Objects that do not emit their own light but reflect the light falling on them. Examples: Moon, Books, Earth, Trees.
Types of Materials (Based on Light Transmission)
Different objects interact with light differently.
| Category | Description | Example |
|---|---|---|
| Transparent | Allow light to pass through completely, so we can see clearly through them. | Glass, Air, Clean Water, Cellophane tape |
| Translucent | Allow only a part of light to pass through. We cannot see through them clearly. | Butter paper, Ground glass, Muddy water, Fog |
| Opaque | Do not allow any light to pass through. We cannot see through them at all. | Wood, Metals, Cardboard, Brick wall |
Formation of Shadows
A shadow is the dark patch formed when an opaque object comes in the path of light.
Three things are strictly required for a shadow to form:
- A source of light.
- An opaque object to obstruct the light.
- A screen (like a wall or ground) where the shadow can fall.
Light Source ------> Opaque Object ------> Screen (Shadow is formed here)
[Bulb] [Apple] [Wall]Characteristics of a Shadow:
- A shadow is always black or dark, regardless of the colour of the opaque object.
- A shadow only shows the outline (shape) of the object, not the details.
- The size of the shadow depends on the distance between the source of light, the object, and the screen.
- Closer to the light source = Bigger shadow.
When you hold your hand up in the sunlight and see a shadow on the floor, the floor acts as the screen!
The Pinhole Camera
A pinhole camera is a simple device that works on the principle that light travels in straight lines (Rectilinear propagation of light).
- It produces an inverted (upside down) image of an object on a translucent screen.
- Used to image bright objects like the Sun or brightly lit trees.
graph LR
A[Tree Top A] -- Straight Line Ray --> B(Pinhole)
C[Tree Bottom B] -- Straight Line Ray --> B(Pinhole)
B --> D[Inverted Image Bottom A']
B --> E[Inverted Image Top B']Mirrors and Reflections
When light falls on a shiny or polished surface like a mirror, its direction changes. This bouncing back of light is called reflection.
Reflection helps us see the exact image of our face in the mirror (not a shadow!). A smooth, highly polished surface like silvered glass makes an excellent mirror. Unlike a shadow, the image formed by a mirror shows the colour and details of the object and is upright (erect), though laterally inverted (left appears right).