The law of reflection
states that for a given beam of light, incident
on the surface of a reflective material,
the angle at which the beam is incident on a
surface will be equal to the angle at which it
reflects off the
surface with respect to the normal line (an
imaginary line perpendicular to the plane of
the surface at
the point of incidence/reflection). In the image above, Theta1 and Theta2
represent the respective angles relative to the normal line of the surface. A
plane mirror is illustrated meaning the surface is smooth and flat across the
horizon.
Above, to the left, we see what the law of
reflection looks like when we stand in front of
a mirror.
Notice the trajectory by which the ray of light
travels as it leaves the light source, reflects,
and travels
away from the mirror. The trajectory is confined
to a plane by the law of refection.
This can be observe by studying where you must
stand in room in order to see
another part of that room reflected back towards
your eyes.
ii. Snell's
Law of Refraction
The refraction of light
through a median is determined by that medians
index of refraction. The index of refraction
of a given material is a property of the
material
itself and it is a factor in determining how
much light bends as it passes through a
material.
If a beam of white light (light containing
all colors in the visual spectrum) passes
through a prism, the different colors
(wavelengths) of light will bend by specific
degrees in a given material, varying
slightly due to wavelength. This slight
variation is observed as a rainbow by human
eye.
Light may bend so drastically as it passes
through material with a high enough index of
refraction that it can appear to slow down;
however, this is not true . The path
of the light is being altered, and therefore
it can take longer for it to travel through
a given material, but the light itself never
slows down during this process.
iii. Lenses
Lenses are thin
pieces of shaped, generally
transparent, material that can
redirect light towards different
trajectories
depending on their shape and size. The
dynamics of lenses can be understood to a
degree by connecting what we have discussed
so far
regarding the laws of reflection and
refraction.
As illustrated in the image below we see
beams of light how as they travel from a
source at A., through the first small lens,
converging
to form a smaller, inverted image at B.. The
image at B then becomes the source of light
for the second, large lens, and the beams
travel from B., through the lens, to
form the final image at C.
Beams
of light which travel through a converging
lens, as shown below, converge to a
specific point on the other side: this
is defined as the focal point of the lens. The
focal point is measured as the distance from
the center of the lens to the spot
where the rays converge:
iv.
Vision
The anatomy of the human
eye is designed to takes advantage of how
light operates using a dynamic similar to what
we have
discussed concerning lenses.
A.
B.
Image A, above, is a basic diagram,
illustrating some of the key structures of the
eye.
Light passes through the eye, into the pupil,
where the light is then directed by the lens
of the eye to converge at a point at the back
of the eye. At this point the image
information
travels along the optical nerve, and will end
up relayed to the visual cortex of the brain,
where
the brain then constructs the final
visualization of what an observer perceives.
Image B, illustrates what it looks like when
our eyes use light to form an image. Notice
how the object
in the eye forms inverted and smaller than the
source. This is due to the shape of the "lens"
of the human eye.
The brain itself is responsible for
re-flipping the image we ultimately perceive
as reality.
v. Focus
The human eye is typically able to focus on
things very far away: the farpoint
of the eye's focus is said to be infinite.
The nearpoint, where the eye can
focus on things up close, is on average,
about 25cm in front of the lens of the eye.
It is accepted that
the variation of focus achieved by the eye
is a property of the lens of the eye which
the light passes through.
The pupil diameter (width) aids in image
clarity, the iris helps adjust the
diameter as needed. When the pupil is
dilated to a small width, less light can
pass
into the eye and therefore the light is
not as intense. In a low lit room, the
pupil will dilate to become wider, so as
to pick up as much
light as possible.
As we
observe commonly, the human eye is not
always perfect at focusing correctly.
The condition of hyperopia, above
(left),
better known as farsightedness, is when
a person can only focus on things at a
far distance from their eyes.
Light from objects up-close is focused
too late by the lens of their eye to
form a decent image.
Myopia, or nearsightedness, is when a
person is easily capable of focusing on
things up close, but when they focus for
away,
the eye converges the light rays too
soon (before it reaches the back of the
eye) causing objects at a distance to
appear blurry.
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