Transcript Diverging lenses

The Nature of Light
Light Can Act Like Waves or
In 1801 Thomas Young an English
scientist did an experiment.
– Double slit experiment
Passed a beam of light through two narrow
openings and projected it onto a screen.
He found the light produced a striped pattern
which meant the light was constructively and
destructively interfering.
This meant that light is composed of waves.
But Light can Also Behave like a
Particle
Other observations indicated that light can also
act like a particle:
– When light hits metal it knocks electrons off the
surface.
– They found that red light cannot knock electrons off
metal no matter how bright it is.
– If light were a wave then the brighter light should have
more energy.
– Photons , light particles contain certain amounts of
energy based on the frequency and wavelength of
light.
– Blue light has a higher frequency and shorter wavelength thus
contains more energy than red light.
Light Energy is Proportional to
Frequency
The higher the frequency of light the more
energy.
The speed of light depends on the medium
it is traveling through.
– Light travels the fastest through a vacuum.
3.0 x 108 m/s
Light slows down in denser mediums.
The Brightness of Light Depends
on Intensity
Intensity
– The quantity of light illuminating a surface.
– Depends on the amount of light passing
through a certain area or space.
– Light spreads out in spherical wave fronts.
– Light is more diffuse further from its source.
Reflection and Color
Reflection
– When light bounces off a surface.
– Rough surfaces reflect light rays in many directions.
Diffuse reflection
Causes a blurry image or no image.
Incident ray
– Ray hitting the surface
Reflected ray
– Ray bouncing off the surface
Normal
– An imaginary line that is perpendicular to the surface the light is
reflecting from.
Angle of Incidence
– Angle between incident ray and the normal.
Angle of reflection
– Angle between the reflected ray and the normal.
The angle of incidence equals the angle of reflection.
Flat Mirrors
Plane mirrors (flat mirrors)
– Create virtual images
Images you see from the apparent light path not
the actual path.
– Images are the same size as the object and
they appear the same distance in the mirror
as the object is in front of the mirror.
Curved Mirrors
Concave mirrors are curved inwards
– Create real images
Real images are produced when light is focused in front of
the mirror.
Can be projected onto a screen.
Are usually inverted.
– Create virtual images
When the object is between the focus and the mirror.
The image is larger than the object.
These are magnifying mirrors.
Curved Mirrors
Convex mirrors are curved outwards
– Are diverging mirrors
– Create virtual images
– Images are always smaller
– Panoramic mirrors
Security mirrors
Side view mirrors on cars
Seeing Colors
The frequency and wavelength of light
determine what color you will see.
– When you optical receptors perceive a wavelength of
550 nm you see green light.
– The colors that you see are a result of surfaces
reflecting various wavelengths of light back to your
eyes.
– White light
When all of the primary colors are being reflected back to
your eyes.
– No light (or black)
When all of the primary colors are being absorbed and no
light is being reflected back to your eyes.
Primary Colors
• The primary colors are
– Red Blue Green
• Your eyes only have receptors for the
frequency of light in these three ranges.
• Every other color you percieve is a
combination of these three wavelengths in
various proportions.
• Adding any two of these colors gives you
the secondary colors or primary pigments
Primary Pigments
• Pigments are substances that absorb light.
• The primary pigments are:
– Cyan Magenta Yellow
• These are also known as the subtractive
colors.
– Adding any of these two colors together give
you back the primary colors.
Refraction of Light
Refraction
When light waves bend in a medium due to the
change in density.
The angle of refraction is NOT equal to the angle
of reflection.
The angle of incidence will be greater than the
angle of refraction if the medium the light is
traveling into is denser.
Refraction
Refraction
Refraction makes objects appear in
different positions from where they actually
are.
– These are virtual images.
– Refraction due to the atmosphere is known as
a mirage.
– Heating air near the surface of the Earth on a
hot day causes the air near the ground to be
less dense than the air above it.
Internal Reflection
Total internal reflection
– Occurs when light is refracted so much that it
is reflected back into a substance.
Critical angle
– When the angle in which light rays meet the boundaries
between the two mediums is so large that the boundary
acts like a mirror and reflects all of the light back into the
medium.
Internal reflection is used in fiber optic cables.
Total Internal Reflection
Lenses
A curved piece of glass or plastic that changes
the direction of light waves.
– Light is refracted when it enters glass and then again
when it leaves the glass.
– Converging lenses
Bend light inward and focus light
Create virtual and real images
Also called convex lenses
– Diverging lenses
Bend light outward
Create virtual images only
Also called concave lenses
Convex and Concave Lenses
Concave and Convex Lenses
Convex Lens Application
Magnification
– When the image is a different size from actual
object.
Microscopes
Telescopes
Lens of the Eye
Glasses or contact lenses
Cameras
Near Sighted and Far Sighted
Near sightedness
– Occurs when the eyeball is too long causing
the image to be to far in front of the retina.
Diverging lenses move the image back so that the
image appears on the retina.
Far sightedness
– Occurs when the eyeball is to short and the
image appears to far behind the retina.
– Convex lenses move the image up
Anatomy of the Human Eye
The Eye Uses a Convex Lens
Nearsightedness
Diverging Lenses Correct
Nearsightedness
Farsightedness
Converging Lenses Correct
Farsightedness
Dispersion and Prisms
Dispersion
– When light is refracted in such a way that it
separates light into its individual color
components.
– Prisms are triangular pieces of glass that
bend light.
The angled surface causes the difference
wavelengths of light to separate because they
bend at different angles.
Water droplets act like prisms and create
rainbows.