Transcript Light - RPDP

Light
Chapter 19
EM Spectrum
•
Electromagnetic
Spectrum (EM) includes radio
waves, microwaves,
infrared waves,
ultraviolet rays, xrays, gamma rays,
and visible light.
Electromagnetic Waves
• Are transverse waves
that are produced by
the motion of
electrically charged
particles. These
waves are often
called
electromagnetic
radiation because
they radiate from
particles.
EM Waves
• Do not need a medium to transfer energy.
• They can travel through a vacuum at a
speed of 300 000 km/s.
Describing EM Radiation
• All EM waves travel at the same speed in
a vacuum, but their frequency and
wavelengths can vary.
EM Spectrum
• Low Frequency, Long-wave length radio
waves to high frequency, short wavelength
gamma rays.
• Page 529.
EM Waves
• Radio Waves
• Infrared Radiation
• Visible Radiation- only part of spectrum
we can see.
• Ultraviolet Radiation –
• X-Rays and Gamma Rays
Light Facts
• A. Light travels in a
straight line at a speed of
300,000 km per second.
• B. Light needs no
medium in order to travel.
It can move through a
vacuum.
• C. When light strikes
matter three things can
happen – it can be
absorbed,
• reflected, or
transmitted.
Absorbed
• Light that is absorbed
is taken in by the
matter it strikes.
• Black objects absorb
all light-best color
for absorption.
Reflected
• Light that is reflected
bounces off the
substance it strikes.
•
Example: Mirrors
Transmitted Light
• Light that is transmitted passes through the
matter it strikes.
• Examples: Window glass, water, and air.
• Translucent – objects that you can see light
through but not
• any details examples are waxed paper and
frosted glass.
• Opaque substances cannot be seen through at
all
• Examples: wood and metal.
Reflection
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Reflected light is
bounced light.
How to predict how
reflected light will
behave.
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A single beam of light is
called a ray.
Incident ray is the ray
that hits a mirror.
Reflected ray is the ray
that bounces off the
mirror.
Refraction
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Light travels in a straight line.
Light can bend and change
direction ie. Reflection,
refraction
Refraction is when light
passes at an angle from one
medium into another medium
so it changes direction or
bends.
Example: you may have
experienced refraction when
reaching into a fish tank to
pick up an item.
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•
Light travels at different speeds through
different mediums.
The speed light travels depends upon
the density of the medium.
– Light that moves straight on from one
medium to another does not bend. It is not
refracted.
What is the spectrum?
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Prism is an object that breaks up light into the
visible spectrum.
Colors of the visible spectrum ROY G BIV
(order never changes) red, orange, yellow,
green, blue, indigo, violet
Variety of colors depends upon the frequency
of light energy.
Every color has a different frequency.
Red has the lowest frequency. And violet has
the highest frequency.
What gives an object its color?
•
The color we see
depends upon
whether the object is
opaque or
transparent. The
color also depends
upon how much of the
light is reflected,
absorbed, or
transmitted.
What color do you see?
• Concave Concave
MirrorMirror
Focuses
Colors
Focuses Colors
Opaque Objects
• Opaque Objects – The color of the object
is the color reflected. Red objects reflect
red light.
– White objects reflect all the colors that make
up white light.
– Black objects absorb all colors that strike it.
Transparent Objects
• Transparent Objects – The color of a
transparent object is the color that passes
through the object. (all other colors
absorbed).
• Transparent objects transmit only some
colors and others are absorbed or blocked
– these substances are called filters.
What is a lens?
• Lens is a transparent
substance that bends or
refracts light in a definite
way.
• Can be glass or plastic.
• Found in every optical
device ie. Binoculars,
telescopes…
• Have one or two curved
surfaces.
Two main types
of lenses
convex lens is thicker at the center than at the
edge. Magnifies to make things look bigger.
• A convex lens focuses light rays. The
point where the light rays meet or
converge is called the focal point.
• Used in projectors and cameras.
Concave lens
This lens is thinner at the center than at
the edge.
• Makes things look smaller
• Spreads out light rays.
• Often used with convex lenses to give a
sharper image.
How do we see?
• Eye has several transparent parts.
• Each part refracts light that enters the eye.
• In a normal eye, light rays converge
exactly upon the retina.
• The retina is the back part of the eye,
made of two kinds of nerves.
– Rods - sensitive to brightness but not color.
– Cones –sensitive to color.
How do eyeglasses help?
• Normal eyes see clearly. The light rays
enter the eye and converge upon the
retina. Some eyes however, the length of
the eyeball is not right. It is either too long
or too short which causes the image to be
out of focus.
Two types of blurred vision:
– near sightedness – slightly longer eye. Light
rays meet in front of retina. Corrected by
concave lenses.
– Farsightedness – slightly shorter eye. Light
rays meet beyond the retina. Corrected with
convex lens.
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Draw Concave lens
Draw Convex Lens
Convex Lens is Inverse
of Concave Lens
• Convex Lens is Inverse
of Concave Lens
Convex Lens is Inverse
of Concave Lens
• Image Formation with Lenses If object is
far from the
lens (beyond)
the focal
point, a real
inverted image
is formed