. What usually happens when a wave reaches a boundary between
two media?
it is reflected
. The return of a wave back to its original medium is called
reflection
Explain what happens when a spring is attached to a wall and you send
a pulse along the spring's length.
all of the wave energy is reflected back along the spring rather
than transmitted into the wall. Waves that travel along the spring are
almost totally reflected at the wall.
Is the following sentence true or false? Shiny metals, such as
aluminum and silver, reflect almost all the frequencies of visible light.
true
When light shines perpendicularly on the surface of still water or
glass
only a very small percentage of its energy is reflected; the rest is
transmitted
a line perpendicular to a surface
normal
the angle between the incident ray and
the normal
angle of incidence
the angle between the reflected ray and
the normal
angle of reflection
the relationship between the angle of
incidence and angle of reflection
law of reflection
an image that appears to be in a location
where light does not really reach.
virtual image
Can your eye tell the difference between an object and its virtual
image? Explain.
Your eye cannot ordinarily tell the difference between an object and its
virtual image because the light that enters your eye is entering in exactly
the same manner as it would without the mirror if there really were an
object where you see the image.
The virtual image formed by a convex mirror (a mirror that curves
outward) is
smaller and closer to the mirror than the object is
When
the object is close to a concave mirror (a mirror that curves inward like a
"cave"), the virtual image is
larger and farther away than the object is.
When light is incident on a rough surface, it is reflected
in many
directions
the reflection of light from a rough surface
Diffuse reflection
Whether a surface is a diffuse reflector or a polished reflector depends on
the wavelength of the waves it reflects
We see most of the things around us by
diffuse reflection.
Sound energy not reflected
absorbed or transmitted.
An echo is reflected sound. The fraction of sound energy reflected from
a surface is _________ when the surface is rigid and smooth, and ______
when the surface is soft and irregular.
greater smaller
The study of the reflective properties of surfaces and sound
acoustics
When the walls of a room, auditorium, or concert hall are too reflective,
the sound becomes
garbled
multiple reflections of sound
waves
reverberations
When a wave that is traveling at an angle changes its speed upon
crossing a boundary between two media
it bends
bending of a wave as it crosses the boundary between
two media at an angle
Refraction
lines that are drawn to represent the
positions of different crests
wave fronts
Sound waves are refracted when parts of a wave front travel
at
different speeds
Sound wave refraction occurs
in uneven winds or when sound is
traveling through air of uneven temperature.
On a cold day or night, when the layer of air near the ground is colder
than the air above it,
the speed of sound near the ground is reduced
Changes in the speed of light as it passes from one medium to another,
or variations in the temperatures and densities of the same medium,
cause
refraction
When light rays enter a medium in which their speed decreases, as when
passing from air into water, the rays bend
toward the normal
When light rays enter a medium in which their speed increases, as when
passing from water into air, the rays bend
away from the normal
A mirage is caused by
the refraction of light in Earth's atmosphere
The appearance of a distorted image that forms as the result of
atmospheric refraction
mirage
On hot days, there may be a layer of very hot air in contact with the
ground. Since molecules in hot air are farther apart, light travels faster
through this air than through the cooler air above it. The speeding up of
the part of the wave nearest the gro
gradual bending of the
light rays, which can produce a mirage.
When you watch the sun set, you see the sun for several minutes after
it has really sunk below the horizon. This is because
light is refracted by
Earth's atmosphere.
Since different frequencies of light travel at different speeds in
transparent materials, they will
refract differently and bend at
different angles
The average speed of light is less than
c in a transparent medium
Light of frequencies closer to the natural frequency of the electron
oscillators in a medium travels more slowly in the medium. This is
because
there are more interactions between the light and the medium.
Since the natural or resonant frequency of most transparent materials is
in the ultraviolet part of the spectrum,
visible light of higher frequencies
travels more slowly than light of lower frequencies.
When light is bent twice at nonparallel boundaries, as in a prism,
the separation of the different colors of light is quite apparent. This
separation of light into colors arranged according to their frequency is
dispersion.
In order for you to see a rainbow,
the sun must be shining in one part
of the sky, and the water droplets in a cloud or in falling rain must be in
the opposite part of the sky
Each raindrop disperses a
full spectrum of colors
. If violet light
from a single drop enters your eye
red light from the same drop falls
below your eye
The dispersed light of other colors in a rainbow is
along similar arcs,
each at their own slightly different angle. Altogether, the arcs for each
color form the familiar rainbow shape.
Total internal reflection occurs when
the angle of incidence is larger
than the critical angle
The critical angle is the angle of incidence that results in light being
refracted at
an angle of 90� with respect to the normal
When a flashlight submerged in water is tipped beyond the critical angle
(48� from the normal in water), the beam of light cannot enter the air; it is
only reflected. The beam is experiencing _________________________which
is the complete reflection of li
total internal reflection
Total internal reflection is as the name implies: total�100%. Silvered
or aluminized mirrors reflect only
90 to 95% of incident light
The critical angle for a diamond is
24.6�,
A diamond's small critical
angle, plus the pronounced refraction within the material, produces
wide
dispersion and a wide array of brilliant colors
sometimes called light pipes, are transparent fibers that
pipe light from one place to another
Optical fibers
the minimum angle of incidence for which a light ray is totally reflected within a medium
critical angle