Name: __________________________________________ Period: _________ Date: _____________
Light and Optics
Section 1: Intro to Electromagnetic Waves
The Electromagnetic Wave Characteristics:
 Require no medium
 Transverse waves of oscillating electromagnetic fields
 Transverse waves move perpendicular to the direction
the wave moves
 The electric and magnetic fields are at right angles to
each other
 All electromagnetic waves travel at 3.0 x 108 m/s
Activity 1: Fill in the
1. Label all the parts of the
electromagnetic spectrum in order
of increasing frequency.
2. Radio Waves, Microwaves,
Infrared, Visible Light, Ultra
Violet, X-rays, Gamma Rays
3. Label the trend lines as well
Section 2: Electromagnetic Wave Math
Speed of light distance-time calculations
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V=λ•f
Velocity = 3.0 x 108 m/s for all electromagnetic waves
If you see any of these you have an electromagnetic wave and v = 3.0 x 10 8 m/s
Radio Waves, Microwaves, Infrared, Visible Light, Ultra Violet, X-rays, Gamma Rays
Example 1: The AM radio band extends from 5.4 x 105 Hz to 1.7 x 106 Hz. What are the longest and shortest wavelengths in this
frequency range?
Example 2: What is the frequency of an electromagnetic wave if it has a wavelength of 1.0 km?
Example 3: How long does it take for light from the sun to reach Earth if the sun is 1.5 x 10 11 m away?
Section 3: Visible Light and Colors
White Light Characteristics:
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“White” light is a combination of red, orange, yellow, green, cyan, blue, and violet
A prism can separate these colors out
o By refraction of different wavelengths of color
From Red:
To Violet:

Longest Wavelength
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Shortest Wavelength
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Lowest Frequency

Highest Frequency
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Least Energy

Most Energy
Activity 2:
• List the colors of
the rainbow in
order from lowest
to highest
frequency
• Color this at home
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Primary Colors
o Red
o Blue
o Green
Secondary Colors: Mixture of 2 Primary Colors
o Magenta (Blue and Red)
o Cyan (Blue and Green)
o Yellow (Red and Green)
A mixture of all three primary colors produces white light
Since secondary colors are a mix of two primaries, mixing primary and secondary colors produces white light
o White Light
= Primary Color + Secondary Color
o White Light
= Blue + Yellow
o White Light
= Green + Magenta
o White Light
= Red + Cyan
Activity 3:
White Light = Primary Color + Secondary Color
White Light= ___________+ ____________
White Light= ___________+ ____________
White Light= ___________+ ____________
•
•
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Primary colors (light)
– Red
– Blue
– Green
Primary pigments (ink)
– Magenta
– Yellow
– Cyan
Primary colors are secondary pigments
Primary pigments (ink) are secondary colors
Section 4: Refraction of Light
• Optics is the science that describes the behavior and properties of light and the interaction of light with matter.
• Refraction- Bending of light as it travels from one medium to another.
• Refraction occurs because lights velocity changes in another medium.
• Light does not need a medium but it is affected by it.
• Light travels from the object to the observers eyes
• Light travels at different speed indifferent medium
(a) Into slower medium light bends toward the normal line
(b) Into faster medium light bends away from the normal line
•
Index of refraction (n)- the ratio of speed of light in a
vacuum to speed of light in that substance.
–
Always greater than 1 because light in a vacuum
is the fastest
(n = 1.00 for a vacuum)
–
Has no unit
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–
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n = index of refraction
c = speed of light in a vacuum
v = speed of light in medium
Example 4: Tom, a watchmaker, is interested in an old timepiece that’s been brought in for a cleaning. If light travels at 1.90 x 10 8 m/s in
the crystal, what is the crystal’s index of refraction?
Example 5: How fast does light travel in fluorite (n=1.434)?
•
Snell's Law- a formula that describes the angle of incidence and angle of refraction
(ni)(sin Θi) = (nr)(sin Θr)
ni = index of refraction of first medium (incidence side)
Θi = angle of incidence
nr = index of refraction of second medium (refracted side)
Θr = angle of refraction
Example 6: A light ray traveling through air (n=1.00) strikes a smooth, flat slab of crown glass (n=1.52) at an angle of 30.0° to the normal.
a. Find the angle of refraction.
b. Draw a picture and label it.
Example 7: Find the angle of refraction for a ray of light that enters a calm lake at an angle of 25° to the normal. (nair = 1.00 and nwater =
1.33)
Section 5: Critical Angle
• Critical angle- Angle at which there would be no
refraction; only total internal reflection.
•
Critical angle equation (θc = critical angle)
Example 8: A jeweler must decide whether the stone in Mrs. Harder’s ring is a real diamond or a less-precious zircon. He measures the
critical angle of the gem and finds that it is 31.3°. Is the stone really a diamond or just a good imitation? (ndiamond = 2.41, nzircon = 1.92, nair
= 1.00 )
Section 6: Reflection and Intro to Mirrors
• Planar reflection -off of a smooth surface
•
Diffuse reflection - reflection off of a rough of
textured surface.
•
Plane mirrors (flat mirror) produce images that
are:
 Virtual - image that appears behind the plane of the mirror
 Upright – Up in the mirror is the same as the object
 Non-magnified – Appear the same size as if the object was that distance away
 Reversed
Concave (Converging) mirror
Produce two types of images depending on where the object is located
Concave (Converging) Mirror
relative to the focal point
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Real inverted images (object beyond focal point)
Magnified virtual upright images (object between focal point
and surface of mirror)
Why two names?
– Concave: name because of shape
– Converging: name because of what light does
• Light rays bend inward or converge
Convex (Diverging Mirror
Convex (diverging) mirror
Only produce virtual, upright, and smaller images
Why two names?
– Convex: name because of shape
– Diverging: name because of what light does
• Light rays bend outward or diverge
Section 7: Planar Ray Diagram
Activity 4:
Drawing the rays:
1. Draw a ray perpendicular to the mirrors surface and
include its reflection
2. Draw a single ray going at an angle away from the object
to the mirror (Include its reflection)
3. Since the rays don’t cross on the real side of the mirror,
after the reflection, extend them until they meet on the
virtual side.
4. This is where the image would appear, draw the image,
with the top being where the rays intersect
5. Then finish the labeling
The image formed in a planar mirror is
1. Virtual
2. Same size
3. Upright
Variables you need to know
do is the distance to the mirror from the object
di is the distance from the mirror to the image of the mirror
ho is the height of the object
hi is the height of the image
Example 9: Mary sees a reflection of her cat sparkles in the living room window. The image of Sparkles makes an angle of 40° with the
normal, at what angle does Mary see Sparkles reflected?
Section 8: Concave Mirror Ray Diagram
• More variables you need to know for a curved mirror
–
Center of curvature (C) – the center of the curve if it
was a sphere
–
Focal Point (F) – ½ from the mirror to the center of
curvature
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Principal axis- the line that the base of the arrow is on.
Activity 5:
Now analyze the image just formed:
Now analyze the image just formed:
Now analyze the image just formed:
Now analyze the image just formed:
Now analyze the image just formed:
Section 9: Convex Mirror Ray Diagram
Activity 6:
Now analyze the image just formed:
Section 10: Mirror Math
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The object side is always positive for lenses and mirror
math
The image sign depends on image location
The focus is on the side of the center of curvature
• The concave mirror always curves to the real side
and has a positive F
• The convex mirror always curves to the virtual
side and has a negative F
Example 10: A concave mirror has a focal length of 10.0 cm. Locate the image of a pencil that is placed upright 30.0 cm from the mirror.
a. Find the magnification of the image
b. Draw a ray diagram of the situation
Example 11: Mark is polishing his crystal ball that acts like a convex mirror. He sees his reflection as he gazes into the ball from a
distance of 15 cm.
a.
b.
What is the focal length of Mark’s crystal ball if he sees her reflection 4.0 cm behind the surface?
Is the image real or virtual?
Example 12: You look into an empty water bowl from 6.0 cm away and see a reflection 12 cm behind the bowl.
a. What is the focal length of the bowl?
b. What is the magnification of the image?
Section 11: Intro to Lenses
Convex (converging) Lens
Why two names?
– Convex: name because of shape
– converging: name because of what light does
• Light bends inward or converges
Concave (diverging) Lens
Why two names?
– Concave: name because of shape
– Diverging: name because of what light does
• Light bends outward or diverges
do – distance to object
di – distance to image
ho – height of object
hi – height of image
F’ – virtual focal point
2F’ – double virtual focal point
F – focal point
2F – double focal point
Section 12: Concave Lens Ray Diagram
Activity 7:
•
Always produces a:
– Virtual
– Upright
– Smaller image
Section 13: Convex Lens Ray Diagram
Activity 8:
Image Produced by a Convex Lens
• Image produced:
– Outside focal point (F’):
• Real and inverted
• Outside 2F’: smaller
• At 2F’: same size
• Between 2F’ and F’: magnified
– Inside focal point (F’)
• Virtual and upright
Section 14: Lens Math
•
The object side is always positive for lenses and mirror
math
•
The virtual and real image sides are different for lenses
•
A convex lens always has a positive focal length
•
A concave lens always has a negative focal length
Example 13: When Sally holds a convex lens 1.00 m from a snow-covered wall, an image of a 5.00 m distant igloo is projected onto the
snow.
a. What is the focal length of the lens?
b. Draw a ray diagram of the situation
Example 14: A concave lens is placed 5.0 cm in front of a doll.
a) What is the focal length of the lens if the doll’s image appears 2.0 cm on the same size of the lens?
b) Draw a ray diagram of the situation
Example 15: A coin collector is looking at a rare coin 1.0 cm behind a magnifying glass (convex lens) with a focal length of 5.0 cm.
a. What is the distance to the image?
b. What is the image’s magnification?
Section 15: Common Optical Instruments
• Camera- A simple camera consists of a convex lens and a
light sensitive film
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Telescope- Uses two lenses to enlarge an image far away.
How the eye focuses:
•
The ciliary muscle around the eye changes the shape and
thickness of the lens, which changes the focal length of the
lens
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Farsighted (Hyperopia)- trouble focusing on objects
close. The eyeball is too short or the cornea is too flat.
Nearsighted (Myopia)- trouble focusing on objects far
away. The eyeball is too long or the cornea is too curved.
Converging/convex lenses are used to correct
farsightedness.
Diverging/concave lenses are used to correct
nearsightedness.
Section 15: Dual Nature of Light
• Light acts as a wave (through space) and a particle (when it interacts with matter)
–
Waves are energy carried in the disruption of medium. Have
interference patterns when they go through each other.
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Particles have a mass and could not occupy the same space.
Double Slit Diffraction
Wave Proof:
Photoelectric Effect
•
Single slit diffraction on visible light.
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Young further demonstrate the wave properties of light with a double slit film.
When a monochromatic light source is used a pattern of fringes result
Light has interference based on its wave properties
Particle Proof:
• Light acts like a stream of particles when it interacts with matter
• Photoelectric Effect- Ejection of electrons from certain metals when light falls
upon them.
– Requires a high frequency of light
Section 16: Other Light Phenomenon
Laser Light:
• Coherent light- crests and troughs line up (same frequency, phase, and direction)
• Laser- Produces coherent light with the aid of a crystal
•
Diffraction grating and thin films can be used to disperse white light into colors (through diffraction and interference)
Polarization of Light
• Usually rays of light are unpolarized which means they are oscillating in random directions.
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Transmission axis- line along which light is polarized
Light at 90º to the transmission axis cannot pass through.