Transcript PROJECT ON LIGHT

What is light
 Light or visible light is electromagnetic radiation that
is visible to the human eye, and is responsible for the sense
of sight. Visible light has wavelength in a range from about
380 nanometers to about 740 nm, with a frequency range of
about 405 THz to 790 THz. In physics the
term light sometimes refers to electromagnetic radiation of
any wavelength, whether visible or not.
 Primary properties of light are intensity, propagation
direction,
frequency
or
wavelength
spectrum,
and polarization, while its speed in a vacuum, 299,792,458
meters per second (about 300,000 kilometers per second),
is one of the fundamental constants of nature.
Speed of light
 The speed of light in a vacuum is defined to be exactly
299,792,458 m/s (approximately 186,282 miles per second). The
fixed value of the speed of light in SI units results from the fact
that the metre is now defined in terms of the speed of light.
 Different physicists have attempted to measure the speed of light
throughout history. Galileo attempted to measure the speed of
light in the seventeenth century. An early experiment to measure
the speed of light was conducted by Ole Rømer, a Danish
physicist, in 1676. Using a telescope, Rømer observed the
motions of Jupiter and one of its moons, Io. Noting discrepancies
in the apparent period of Io's orbit, he calculated that light takes
about 22 minutes to traverse the diameter of Earth's
orbit. Unfortunately, its size was not known at that time. If
Rømer had known the diameter of the Earth's orbit, he would
have calculated a speed of 227,000,000 m/s
Reflection
 Reflection is the change in direction of a wave front at
an interface between two different media so that the wave front
returns into the medium from which it originated. Common
examples include the reflection of light, sound and water waves.
The law of reflection says that for specular reflection the angle at
which the wave is incident on the surface equals the angle at
which it is reflected. Mirrors exhibit specular reflection.
 In acoustics reflection causes echoes and is used in sonar. In
geology, it is important in the study of seismic waves Reflection
is observed with surface waves in bodies of water. Reflection is
observed with many types of electromagnetic wave,
besides visible light. Reflection of VHF and higher frequencies is
important for radio transmission and for radar. Even hard Xrays
and gamma rays can be reflected at shallow angles with special
"grazing" mirrors.
Laws of reflection
 If the reflecting surface is very smooth, the reflection
of light that occurs is called specular or regular
reflection. The laws of reflection are as follows:
 The incident ray, the reflected ray and the normal to
the reflection surface at the point of the incidence lie
in the same plane.
 The angle which the incident ray makes with the
normal is equal to the angle which the reflected ray
makes to the same normal.
 The reflected ray and the incident ray are on the
opposite sides of the normal.
Plane Mirror
Mirror
Normal
Θi
Θr
Convex mirror
 A convex mirror, fish eye mirror or diverging mirror, is
a curved mirror in which the reflective surface bulges
toward the light source. Convex mirrors reflect light
outwards, therefore they are not used to focus light. Such
mirrors always form a virtual image, since the focus (F) and
the centre of curvature (2F) are both imaginary points
"inside" the mirror, which cannot be reached. As a result,
images formed by these mirrors cannot be projected on a
screen, since the image is inside the mirror.
 A collimated (parallel) beam of light diverges (spreads out)
after reflection from a convex mirror, since the normal to
the surface differs with each spot on the mirror.
Uses of convex mirror
 The passenger-side mirror on a car is typically a convex mirror. In
some countries, these are labeled with the safety warning
"Objects in mirror are closer than they appear", to warn the
driver of the convex mirror's distorting effects on distance
perception. Convex mirrors are preferred in vehicles because
they give an upright, though diminished, image. Also they
provide a wider field of view as they are curved outwards.
 Convex mirrors are used in some automated teller machines as a
simple and handy security feature, allowing the users to see what
is happening behind them. Similar devices are sold to be
attached to ordinary computer monitors.
 Some camera phones use convex mirrors to allow the user to
correctly aim the camera while taking a self-portrait.
Convex Mirror
Concave mirrors
 A concave mirror, or converging mirror, has a reflecting
surface that bulges inward (away from the incident light).
Concave mirrors reflect light inward to one focal point.
They are used to focus light. Unlike convex mirrors,
concave mirrors show different image types depending on
the distance between the object and the mirror.
 These mirrors are called "converging" because they tend to
collect light that falls on them, refocusing parallel
incoming rays toward a focus. This is because the light is
reflected at different angles, since the normal to the surface
differs with each spot on the mirror.
Concave Mirror
Concave Mirrors
Concave Mirror
Concave Mirrors
Concave Mirrors