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• Light – anything which enable us to see things around us.
• Luminous objects – Objects that produces light
• Sources of light can be classified into natural and artificial sources of light
• Natural source of light – Objects that occur naturally and produce their own light are called natural source of light. E.g. sun, fireflies, jellyfish,etc
• Artificial source of light – Manmade objects that produce light are artificial source of light. E.g torch, lamp, bulb, etc.

• Transparent Object	Opaque Object	Translucent Objects
  Objects from which we see thing clearly through Allows light to completely pass through them E.g. Spectacle, glass, clean water, some polythene bags, plastic materials etc.	Objects from which we cannot see through Do Not allows light to pass through them E.g. Walls of the building, books, cardboard, colored water,	Objects from which we can see things but not clearly Allows partial passage of light E.g. Tracing paper, rough glass, thin tissue paper etc.

• Shadow – When you pass a light on opaque object a dark spot appears on the screen. This is the shadow.
• Properties of shadow –
  • Shadow requires opaque object, screen and light source
  • Are formed opposite to source of light
  • Shadows are always black even if object is colorful
  • Shape of shadow changes with the direction of light
  • Size of shadow changes with the change in position of the light source, the opaque object or the screen
• Umbra – Darker part of the shadow
• Penumbra – Lighter part around umbra
• Antumbra – When light source is bigger than the object size, lighter part in penumbra, dark part in umbra and the third part away from the object (i.e. at a distance) is antumbra.
• Working principle of pinhole camera – image formation by pinhole camera one can easily understand that light from top of the object must be going in straight direction through the pinhole to reach at the bottom of the screen. Similarly, light from bottom of the object must be going in straight direction through the pinhole to reach at the top of the screen.
• Watch complete video on pinhole camera here.