```Stefan-Boltzmann Law                                      absolute temperature (in degrees Kelvin),
then E = σT4
   It states that the total radiant heat energy         The constant of proportionality σ, called
emitted from a surface is proportional to             the Stefan–Boltzmann constant or Stefan"s
the fourth power of its absolute                      constant. The value of the constant is
temperature.                                          5.735 × 10−8 Wm-2 K4
   If E is the radiant heat energy emitted
from a unit area in one second and T is the
LIGHT
Light                                                 Plane Mirror and Its Reflection
   It is the natural agent that stimulates sight
and makes things visible.
   The speed of light in a vacuum is 3 x 108
m/s
   Sunlight      is    a    portion    of    the
electromagnetic radiation given off by the
Sun, particularly infrared, visible, and
ultraviolet light. Sunlight on the skin is an
effective source of vitamin D. It takes
about 8.3 minutes to reach the Earth. The
Sunlight reflected from moon takes 1.28 s
to reach earth.
   It is simply a mirror with a flat surface; all
Reflection
of us use plane mirrors every day, so
   Reflection is when light bounces off an               we"ve got plenty of experience with them.
object.                                              The image is the same distance from the
   The incident ray, the reflected ray and the           mirror as the object appears to be (i.e., the
normal to the reflection surface at the               image distance = the object distance)
point of the incidence lie in the same               The image produced is upright.
plane.                                               The image is the same size as the object
   The angle which the incident ray makes
with the normal is equal to the angle             Spherical Mirror and Its Reflection
which the reflected ray makes to the same            It is a mirror which has the shape of a
normal: i  r                                       piece cut out of a spherical surface.
   The reflected ray and the incident ray are           There are two types of spherical mirrors:
on the opposite sides of the normal.                 Concave Mirror : Its inner side of the
surface of a spherical mirror is polished to
reflect light. It converge parallel beam of
light.
   Convex Mirror : Its outer side of the
surface of a spherical mirror is polished to
reflect light. It diverge parallel beam light.
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