Transcript HP Unit 11-light & optics - student handout

• In 1865, James Clerk
Maxwell showed that
light is comprised of
both electricity and
magnetism.
James Clerk Maxwell
(1831 – 1879)
Electromagnetic (light) Waves
c=fλ
The speed of the
light wave
remains
constant in a
given medium.
Radiowaves…not just AM & FM
These light waves
are a few cm to
several football
fields in wavelength
Cordless phones,
radios, garage door
openers, RC toys.
AM vs FM radio
Frequency Modulated
Amplitude Modulated
• Both AM & FM radio signals have advantages and
disadvantages.
• Generally, AM waves have much longer
wavelengths than FM waves and can DIFFRACT
better than FM waves and can travel greater
distances before the signal fades. FM is more
direct line of sight.
• However, because information is coded in the
amplitude of an AM wave, power lines and
lightning can influence the amplitude and are
more likely to interfere with the AM wave.
• FM has a greater range of frequency which is
better for music whereas AM is better for talk radio
since there isn’t much fluctuation in a person’s
voice.
Microwaves
Infrared
Infrared picture showing heat
loss for a house.
Pit vipers, pythons, and boas possess special
organs that form images in the brain of the thermal
environment, much like vision occurs in the human
brain. Thus, these snakes "see" heat, and this
amazing system is the most sensitive infrared
detector on Earth, natural or artificial.
BOSTON BOMBER 2013
Visible
Ultraviolet
X-RAYS
• In 1895, W.C. Röntgen
discovered mysterious rays
capable of passing through
the human body.
• Mostly used for medical
and industry
Gamma Ray
• High-energy photons are emitted as one of
three types of radiation resulting from
natural radioactivity. Differs from X-rays
where radiation is emitted by excited
nuclei rather than electrons
• Gamma ray sources are used for cancer
treatment and for diagnostic purposes
• Highest energy EM wave, highest f,
shortest wavelength, most penetrating,
most damaging of all EM waves
Reflection and Refraction
Rays instead of waves
A ray of light is an imaginary line drawn
along the direction of travel of the light
beams. We use this instead of a wave.
Law of Reflection
The normal is a line
perpendicular to the surface
θi
Specular Reflection:
Diffuse Reflection:
With diffuse reflection, your eye sees reflected light
at all angles. With specular reflection (from a mirror),
your eye must be in the correct position.
Which photo demonstrates
specular reflection?
Sun & moon reflect in a line
If water was
smooth you would
just see reflection
of object as in
picture at left.
But the surface is
rougher where
waves act like an
array of flat mirrors
reflecting is such a
way as shown
below. The light
then appears
smeared into a
long vertical
column.
Refraction of Light
Same as waves/sound unit. Bending due to a speed change
due to material change entering at an angle.
Identify #1-5
θi>θr
θi<θr
θi
θi
θr
θr
The Index of Refraction
Some Indices of Refraction
Snell’s Law of Refraction
Example: A ray of light is incident on the
surface of a block of clear ice (1.309) at an
angle of 40.0° with the normal. Part of the light
is reflected and part is refracted. Find the angle
between the reflected and refracted light.
Example: The light emitted by a helium–neon laser
has a wavelength of 632.8nm in air. As the light
travels from air into zircon (1.923), find
a) its speed in zircon
b) its frequency in zircon
c) its wavelength in zircon.
Illusions from refraction
Objects appear ‘bent’ or
disjointed.
Objects appear
‘higher’
Our eye-brain system fools us and we conjure up
an image since we cannot follow the path of
refraction
Romantic Sunset not really there!?
What will I tell my lover!!
Water on the road mirage
“Seeing heat” mirage
Dispersion
Variation of Index of
Refraction with Wavelength
• Violet light refracts
more than red light
when passing from
air into a material
Critical Angle
θc
Total Internal Reflection
When you exceed θC
Diamonds
Fiber Optics and T.I.R.
A bright underwater flood light at the bottom of a 2.75m
deep pool is positioned 1.85m from one edge of the
pool. At what angle will light emerge from the surface of
the water at the edge of the pool with respect to
ground. Assume the pool is filled to the brim with water.
ground
light
Image Types for Mirrors
Image characteristics:
A) TYPE –
B) ORIENTATION C) MAGNIFICATION (M) -
D) Position & height of image and object -
Reflection & Image
Formation by a Plane Mirror
Characteristics of the Image
Formed by a Plane/Flat Mirror
Concave Mirror
Parallel light rays reflecting off of
concave mirror
Note how all 4 rays reflect and
converge at common point.
This is called FOCAL POINT.
Focal Length
Incoming rays are parallel
and all reflect through a
common point called the
The distance from the mirror
to the focal point is called the
The focal length is ½ the
radius of curvature f= R/2
Applications of concave mirror:
Behind flashlight bulbs, headlights,
searchlights.
SATELLITE DISH -
SOLAR COOKER
Convex Mirror
APPLICATIONS:
RAY DIAGRAMS
Object inside the focal point.
Characteristics of image:
IMAGE IN CONVEX MIRROR
Mirror equation
Magnification
Sign Convention: Reflective side of mirror is
positive & back side of mirror is negative
Negative magnification or hi = inverted image
Example
A concave makeup mirror is designed so that a
person 25cm in front of it sees an upright image
magnified by a factor of two. What is the radius of
curvature of the mirror?
Example2
How far from a concave mirror with a focal length
of 22.5 cm must an object be placed to produce
an image with a magnification of +3.65?
Thin Lenses
Converging or Convex Lenses
(THICKER AT CENTER)
Parallel rays refract through converging lens
and then proceed through F on other side.
Diverging or Concave Lenses
(THICKER AT EDGES)
Parallel rays refract through diverging lens
and then diverge where rays can be traced
backwards through F on incident side.
Ray Diagram
Diverging lens
Sign convention for lenses
Where you expect light to end up is assumed
positive (opposite side of lens)
Converging lenses have +f
Diverging lenses have -f
Example
Based on the picture
shown, describe the
type of lens and the
type of image
If the magnifying glass was immersed in water,
what effect (if any) would that have on the rays
leaving the lens?
APPLICATIONS OF LENSES
• Overhead projector (lens + mirror),
eyeglasses, contacts, magnifying glass,
telescopes, microscopes, your eye, etc
Lenses and your EYE
• The ability of the eye
to instantly adjust its
focal length is known
as accommodation.
• Your ciliary muscles
flex and manipulate
the curvature and
shape of your lens
which changes the
focal length of the lens.
Farsighted
Nearsighted
• Astigmatism means that the cornea
is oval like a football instead of
spherical like a basketball. This
causes light to focus on more than
one point in the eye, resulting in
blurred vision at a distance or near.
Combinations of Lenses
Combination of Thin Lenses
• The image produced by the first lens is calculated
as though the second lens were not present
• The light then approaches the second lens as if it
had come from the image of the first lens
• The image of the first lens is treated as the object
of the second lens
• The image formed by the second lens is the final
image of the system
• If the image formed by the first lens lies on
the back side of the second lens, then the
image is treated at a virtual object for the
second lens
do will be negative – virtual objects CAN form
real images
• The overall magnification is the product of
the magnification of the separate lenses
Example
An object is located 4.75m from a simple optical
system consisting of two converging lenses. The
first lens of this system has a focal length of 100mm
and the second lens, which is 20.0cm from the first
lens, has a focal length of 150.0mm. What is the
magnification of the system?
Example 2
An object is placed 20.0cm to the left of a
converging lens of focal length 25.0cm. A
diverging lens of focal length 10.0cm is 25.0cm
to the right of the converging lens. Find the
position and magnification of the final image.