Sun makes its presence felt through the rays of light. The path
of the rays can be modified in several ways such as reflection,
refraction etc. The first experience of modification of light
rays for school kids is through the experiment where a lens
is used to burn a piece of paper. The modification of the path
of light rays using lenses and the concept of measuring time
using sunlight is brought together in 'Surajkiran', meaning
'sunray' in Hindi.
this concept a planoconvex lens is held horizontally at a height
equal to its focal length , with the convex surface facing the
ground. The light from the Sun, after refraction in the lens,
converge to form a bright spot on the ground. The spot falls
at different places depending upon the position of the Sun relative
to the lens. At noon the spot falls directly below the lens.
In the evenings and mornings the spot is farthest from the noon
position, on opposite ends. Concentric circles on the surface
below the lens with the noon position of the bright spot as
the centre is used to approximately gauge the time. At one level
'Surajkiran' is a simple device to gauge the time using the
concept of refraction of light. At an other level it can be
used as an educational tool to teach the principles of light.