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- Objects like the sun that give out or emit light of their own are called luminous objects.
- Objects like moon that do not give out or emit light are called non-luminous objects.
- If an object allows light to pass through it, then it is transparent object.
- If an object does not allow light to pass through it, then it is opaque object.
- If an object allows only partial light to pass through it, then it is translucent object.
- The dark patch formed, when an opaque object opposes the passing of light, is known as shadow.
- Shadows give us some information about shapes of objects but sometimes mislead also.
- Three things needed to form a shadow are: an opaque object, an opaque screen and a source of light.
- Light travels in a straight line.