Transcript CHAPTER-17 Light and Image Formation

CHAPTERS-16 &17
Light
Outline:
1. Electromagnetic waves
2. Human eye and color
3. Reflection and Image Formation
4. Refraction of Light
5. Lenses and Image Formation
6. Focusing Light with Curved mirrors
7. Eyeglasses, Microscopes, and Telescopes
Everyday Phenomenon:
Rainbows and Laser Refractive Surgery
Electromagnetic Waves
• An electromagnetic wave consists of time-varying
electric and magnetic fields, in directions
perpendicular to each other as well as to the
direction the wave is traveling.
There is a wide spectrum of frequencies and
wavelengths of electromagnetic waves.
– Different types of electromagnetic waves have different
wavelengths and frequencies.
– Together they form the electromagnetic spectrum.
How do our eyes distinguish color?
– Light is focused by the cornea and lens onto the retina.
– The retina is made up of light-sensitive cells called rods and cones.
– Three types of cones are sensitive to light in different parts of the
spectrum.
How Are Light Rays Related to
wavefronts?
Wavefronts are perpendicular
to the rays.
Reflection
The Law of Reflection
The angle of incidence = The angle of reflection.
i  r
How Are Images Formed by a
Plane Mirror?
How Are Images Formed by a
Plane Mirror?
 How tall must a plane mirror be in order for you
to view your full height reflected in it?
a)
b)
c)
d)
e)
Half your height.
Three-quarters of your height.
A little shorter than your height.
Exactly your height.
A little taller than your height.
Since the light reaching your
eyes from your feet would be
reflected from a point on the
mirror exactly halfway between
your feet and your eyes, you
would be able to view your feet
(and all points between your feet
and your eyes) in a mirror that
was half as tall as you.
Q7
Refraction of Light
Definition Of The Index Of
Refraction
The index of refraction n of a material is the ratio of the speed
c of light in a vacuum to the speed v of light in the material:
Law of Refraction
n1 Sin1  n2 Sin 2 .
Apparent Depth of Fish Is
Smaller Than Actual Depth Due
to Refraction
Total Internal Reflection
Why a Diamond Sparkles?
Why does a diamond exhibit such brilliance? And why does a
diamond lose much of its brilliance when placed under water?
Optical Instruments
Many optical instruments, such as binoculars, periscopes, and
telescopes, use glass prisms and total internal reflection to turn a
beam of light through 90° or 180°.
Prism and Spectrum of
Colors
Dispersion of Light
Rainbow
Primary Rainbow
Water droplet
disperses the
light into
colors.
Secondary Rainbow
Colors are reversed and less intense.
Focal Point (F) and Focal
Length (F)
Ray Diagram
Ray Diagram
Diverging or Negative lens:
Focal Point (F) and Focal
Length (f)
Ray Diagram for Diverging Lens
Lens Equation
Lens Equation and
Magnification, m
E6
Optical Instruments
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Human eye and Vision Defects
Camera
Eyeglasses
Microscope
Telescope
Nearsighted Eye, Myopia
Nearsightedness: can see only nearby objects clearly.
Negative Lens Is Used to Correct Nearsightedness.
Positive Lens Is Used to Correct
Farsightedness
Farsightedness: can see only far objects clearly.
How Does a Microscope Work?
• Used to view small things nearby.
• Consists of two positive lenses, objective
and eyepiece.
• Final image is magnified and inverted.
• Ray diagram can be used to illustrate the
image formation.
Ray Diagram For Microscope
A laboratory microscope has 3 or 4
objective lenses.
Astronomical Telescope