Convex lens can be used to light
up fire by concentrating the sun's rays at a point. Since
the lens is located very far from the sun, the rays reaching
the lens are essentially parallel.
A beam of parallel light rays after passing through a convex
lens converge at its focus. The object which is to be burnt
should be placed at the focus of the convex lens. The lens
focuses not only the sunrays but also their radiant energy
at a single point which lights up fire.
Even ice carved in a shape similar to convex lens can be
used to light fire. The ice to be used should highly transparent
and it'll behave as if it's a convex lens.
If you are still unclear about the concepts, please refer
the animation below.
Besides the animation of the above concepts in detail the
animation file also consists of the following in the explanatory
- what is meant by focal length ?
- Can a concave lens light a fire ?
- Why does paper burn ?
- Can a paper be burnt by focussing light from a bulb
- How can sun situated so far away burn a paper ?