Transcript mirrors - fizika1

MIRRORS
What do you see when you look into the mirror?
A History of Mirrors
A history of the mirror is really the history of
looking, and what we perceive in these magical surfaces can
tell us a great deal about ourselves – whence we have come,
what we imagine, how we think, and what we yearn for.
Mirrors have been featured in folklore, religion,
magic, science, art, and literature. They have appeared in a
myriad of forms and usage that have included revealing,
hiding or distorting reality, as a communication device,
weapons of war, to search the stars, to ward off evil spirits,
for divination,etc.
A mirror is an object with at least one reflective surface.
The most familiar type of mirror is the plane mirror, which
has a flat surface.
Curved mirrors are also used, to produce magnified or
diminished images or focus light or simply distort the reflected
image.
Mirrors are commonly used for personal grooming or
admiring oneself (in which case the old-fashioned term
"looking-glass" can be used), decoration, and architecture.
Mirrors are also used in scientific apparatus such as
telescopes and lasers, cameras, and industrial machinery.
Most mirrors are designed for visible light; however,
mirrors designed for other types of waves or other wavelengths
of electromagnetic radiation are also used, especially in nonoptical instruments.
MIRRORS
Instruments
Telescopes and other precision instruments use front silvered or
first surface mirrors, where the reflecting surface is placed on the front
(or first) surface of the glass (this eliminates reflection from glass surface
ordinary back mirrors have).
For scientific optical work, dielectric mirrors are often used. These
are glass (or sometimes other material) substrates on which one or more
layers of dielectric material are deposited, to form an optical coating.
A dielectric coated mirror used in a dye laser
Mirrors and superstition
It is a common superstition that someone who breaks a mirror
will receive seven years of bad luck.
According to legend, a vampire has no reflection in mirrors
because it is an undead creature and has already lost its soul.
Another superstition claims it is bad luck to have two mirrors
facing each other.
In days past, it was customary in the southern United States to
cover the mirrors in a house where the wake of a deceased person
was being held.
It was believed that the person's soul would become trapped in a
mirror left uncovered. This practice is still followed in other countries
(e.g., Romania), extending to everything that could reflect the
deceased person's face (such as TVs and appliances ).
Mirror in literature - Narcissus
In literature, Ovid
(trans. 1986) warned of
the danger of exclusive
preoccupation of oneself
at the expense of others in
the Greek myth of
Narcissus, who fell in love
with his own reflection.
The mirror’s metaphysical
qualities was explored in
Lewis Carroll’s (1982/2008)
alternate reality in Through
the Looking-Glass, and What
Alice Found .
Through the Looking-Glass, and What Alice Found .
Alice entering the Looking Glass. Illustration by Sir John Tenniel
There, in
the story of
Snow White
(Grimm &
Grimm,
1987/2003) the
magic talking
mirror saw all
that was
happening in
the kingdom,
and the Mirror
of Erised
(Rowling,
2008), reflected
the image of
what the heart
desired most.
For Harry
Potter, it was the
sight of his
deceased family.
Image with mirrors
Image with and in mirrors
Shape of a mirror's surface
In a plane mirror, a parallel beam of light changes its direction as a
whole, while still remaining parallel; the images formed by a plane mirror are
virtual images, of the same size as the original object (see mirror image).
In a concave mirror, parallel beams of light becomes a convergent
beam, whose rays intersect in the focus of the mirror.
In a convex mirror, parallel beams become divergent, with the rays
appearing to diverge from a common point of intersection "behind" the mirror.
Spherical concave and convex mirrors do not focus parallel rays to a
single point due to spherical aberration. However, the ideal of focusing to a
point is a commonly-used approximation. Parabolic reflectors resolve this,
allowing incoming parallel rays (for example, light from a distant star) to be
focused to a small spot; almost an ideal point. Parabolic reflectors are not
suitable for imaging nearby objects because the light rays are not parallel.
Plane mirrors
A mirror, reflecting a vase
Concave Mirrors
Convex Mirrors
Spherical Mirrors
Reflection from Mirrors
Reflection from a Plane Mirror
The image distance always equals
the object distance. The size of the
image is the same as the object (the
mirror does not magnify the image).
Reflection from a Concave Mirror
When the object is far from the mirror, the image is
inverted and at the focal point. The image is real light rays
actually focus at the image location). As the object moves
towards the mirror the image location moves further away
from the mirror and the image size grows (but the image is
still inverted).
When the object is that the focal point, the image is at
infinity. As the object moves towards the mirror inside the
focal point the image becomes virtual and upright behind
the mirror. Initially the virtual image is much larger than
the object and really far away, but as the object
approaches the mirror the virtual image also approaches
the mirror and decreases in size.
Reflection from Convex Mirror
The image produced by a convex
mirror is always virtual, and located behind
the mirror. When the object is far away
from the mirror the image is upright and
located at the focal point. As the object
approaches the mirror the image also
approaches the mirror and grows until its
height equals that of the object.
The Archimedes Heat Ray
Archimedes may have used mirrors acting collectively
as a parabolic reflector to burn ships attacking Syracuse.
The 2nd century AD author Lucian wrote that during
the Siege of Syracuse (c. 214–212 BC), Archimedes
destroyed enemy ships with fire. Centuries later,
Anthemius of Tralles mentions burning-glasses as
Archimedes' weapon.
The device, sometimes called the "Archimedes heat
ray", was used to focus sunlight onto approaching ships,
causing them to catch fire.
Archimedes may have used mirrors acting collectively as a
parabolic reflector to burn ships attacking Syracuse.
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About the Design of Kaleidoscope
A kaleidoscope, or a caleidoscope, is a tube of
mirrors containing loose, colored objects such as beads
and pebbles. The viewer looks in one end and light
enters the other end, reflecting off the mirrors.
Kaleidoscopes operate on the multiple reflections
principle that several mirrors are attached together.
Generally there are two rectangular lengthwise mirrors.
Setting of the mirrors at 45°creates eight duplicate
images, six at 60°, and four at 90°. As the kaleidoscope
tube is rotated, the tumbling of the colored objects
presents the viewer with varying patterns.
Make a Kaleidoscop
- (Physics / General Physics) an optical toy
for producing symmetrical patterns by multiple
reflections in inclined mirrors enclosed in a tube.
Loose pieces of coloured glass, paper, etc.,
are placed between transparent plates at the far
end of the tube, which is rotated to change the
pattern.
- is any complex pattern of frequently
changing shapes and colours.
Kaleidoscop
Bibliography
1. www.thefreedictionary.com/kaleidoscope.
2. en.wikipedia.org/wiki/Mirror.
3. www.kettering.edu/~drussell/Demos/Ray...
4. www.experiencefestival.com/mirror_-_m...
5. www.csicop.org/superstition/library/m...
6. en.wikipedia.org/wiki/Archimedes.
7. www.physicsforums.com/showthread.php%.
8. en.wikipedia.org/wiki/Mirror_image.
PROJECT - MIRRORS
Prepared by:
MIREA DIANA