if you can’t see him, he can’t see you! warm up #1 write the knowns and solve: the wavelength of...
TRANSCRIPT
• If you can’t see him, he can’t see
you!
• Warm up #1 Write the knowns and solve:
• The wavelength of an electromagnetic wave measures 3.63 x 10-10 m. What is the frequency of this wave?
4/16Pick up Light Notes II
Warm Up #1: The wavelength of an electromagnetic wave measures 3.63 x 10-10
m. What is the frequency of this waveform? Is it an infrared wave? Explain.
• f = (3.00 x 108 m/s) / (3.63 x 10-10 m)
• f = 8.26 x 1017 Hz
• TODAY IS LAST DAY FOR MAKEUPS
• Warm up #2
• True or False? Gamma rays have the highest energy in the EM spectrum because they travel the fastest.
4/17Yesterday we startedLight Notes II. Get them out now. No calculators today ↑What kind of image?
Polarized Sunglasses- How do they work?
light waves vibrate in more than one plane
light waves can be made to vibrate in a single plane by use of polarizing filters.
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What are the primary colors of light?
• How do you see color
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Click on this hyperlinked address to access a terrific interactive website doing the above or use a set of flashlights.http://micro.magnet.fsu.edu/primer/java/primarycolors/additiveprimaries/index.html
Eye anatomyBiologix: The eye Vision and
Perception (29min)
What we see:• In visible spectrum 400-700nm
• If you see red, object absorbs all frequencies of visible light but red, ie object reflects red
• White: combination of all visible light frequencies, all frequencies reflected
• Black: combination of all visible light frequencies absorbed, no frequencies reflected
Speed of Light• The speed of all EM Waves (light) or “c” is 3 x 108 m/s.
• What is a light year?
• The distance light travels in one year
• Does light ever go slower?
• Yes, 3 x 108 m/s is the maximum and occurs in an vacuum.
• Light slows as it enters more dense medium.
• When it changes medium, it bends.
• What is this called?
• REFRACTION
Reflection and Refraction at an InterfaceWhy does the light bend?
FYI: The speed of light c in a material is generally less than the free-space velocity c of 3 x108 m/s. In water light travels about three-fourths of its velocity in air. Light travels about two-thirds as fast in glass. The ratio of the velocity c of light in a vacuum to the velocity v of light in a particular medium is called the index of index of refraction,refraction, nn for that material.
nc
v
Mirages
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RainbowsInteresting tidbit: Sun is behind
you for you to see a rainbow
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Rainbows are due to refraction and reflection in water droplets
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Key Terms1. Object
2. Image
3. Real
4. Virtual
5. Plane
6. Convex
7. Concave
8. Converge
9. Diverge
10. Center of Curvature
11. Focal Length/Focal Point16
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Reflection and Mirrors
REFLECTION OF LIGHT Light obeys the law of refection that states that: "The angle of incidence is equal to the angle of reflection."
Angle of Reflection = Angle of IncidenceAngles are measured with respect to the normal line
If all surfaces reflect, why can’t I see my image?
Light reflection from a smooth surface is called regular or specular reflection. Light reflection from a rough or irregular surface is called diffuse reflection.
What type of reflection?
Fiber Optics is also an example of reflectionTOTAL INTERNAL REFLECTION
• Total Internal Reflection!!!
Embedded in counters and other surfaces
F. O. Glove: Replace your flashlight!
Wallpaper
Mirrors
When we look at something in the mirror, the light wave we see is the
reflected ray:
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• Object: source of rays
• Image: reproduction of object
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Describing Images
• Size– Same– Reduced– Enlarged
• Orientation– Upright or inverted, Reversed
• Virtual or Real
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Virtual
• reflected rays do not actually converge to form image.
• Cannot be projected.
• images form where light rays appear to have crossed.
• In mirrors, they form behind the mirror.
• are always upright.
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Real
• images form where light rays actually cross.
• Can be projected.
• In mirrors, they form on the same side of the mirror as the object since light can not pass through a mirror.
• are always inverted (flipped upside down).
Mirages
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RainbowsInteresting tidbit: Sun is behind
you for you to see a rainbow
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Rainbows are due to refraction and reflection in water droplets
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Types of Mirrors
• Flat or Plane
• Convex
• Concave
FLAT MIRRORS A flat mirror reflects light rays in the same order as they approach it. Flat mirrors are made from pieces of plate glass that have been coated on the back with a reflecting material like silver or aluminum.
The image is the same size as the object and the same distance behind the mirror as the object is in front of the mirror.
These images which appear to the eye to be formed by rays of light but which in truth do not exist are called virtual images. On the other hand real images are formed when rays of light actually intersect at a single point.
Notice that the images formed by a flat mirror are, in truth, reflections of real objects. The images themselves are not real because no light passes through them.
Left-Right Reversal
Why?
Mirrors actually reverse you front to back, it is like turning a glove inside out
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Plane Mirrors: flat surface. ex. mirror hanging on the wall in your bathroom
Plane mirror ray diagram
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Plane Mirror
In a plane mirror the object is the same size, upright, and the same distance behind the mirror as the object is in front of the mirror. Your mind extends the reflected ray beyond the mirror to form image.
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Think about your image in a plane mirror?
• What is the same?
• What is different?
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Images in a plane mirror are also reversed left to right.
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• What type of image is shown above?– A. Real– B. Virtual
Original image
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Concave mirrors: sphere whose inner surface was reflective
Concave mirrors: aka converging mirrors since they bring light rays to a focus. ex. magnifying mirrors
Convex mirrors: sphere whose outer surface was reflective.
Convex mirrors: aka diverging mirrors since spread out light rays. ex store security mirrors
Types of Mirrors Convex
Concave
Convex Mirrors
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• What type of mirror created this image?A. Plane
B. Convex
C. Concave
Original Image
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What kind of mirror would be used to focus a beam of light?
• Concave
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Drawing Diagrams• F: Focal Point, point where parallel light rays
converge or appear to diverge. The focal point (F) is located halfway between the mirror’s surface and the center of curvature.
• f: focal length, distance between F and mirror/lens
• C: Center of curvature, geometric center of sphere of radius. C = 2f =radius
• Principle axis: line that passes through both the center of curvature (C) and the focal point (F) and intersects the mirror at a right angle.
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FC
Principle Axis
Concave Mirrors
Light source
Convex Mirrors
F C
Principle Axis
Light source
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C=2f
• f = ?
• C/2
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• A concave mirror has a radius of curvature of 15 cm. What is the focal length of this mirror?
• A. 15 cm
• B. 30 cm
• C. 7.5 cm
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1. Start at top of object. Light ray 1 travels parallel to the principle axis, strikes the mirror, and is reflected back through the focal point (F).
2. Light ray 2 travels from top of object and strikes the mirror, is in line with the focal point. It is reflected back parallel to the principle axis.
3. Where these 2 reflected light rays intersect is the location of the image. Sometimes it is necessary to extend reflected rays beyond mirror. If above axis, erect; if below, inverted.
Ray Diagram Rules
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Hints• Images in front of mirror are always real• Real Images are always inverted• Inverted images are always below the principle
axis• If reflected rays do not cross, extend them
behind mirror• Images behind mirror are always virtual• Virtual Images are always erect• Erect images are always above the principle axis
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Object Location
Real or Virtual
Erect or Inverted
Size
Plane Mirror
Concave Mirror
Convex Mirror
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Locating images in concave mirrors
Fill in hypertextbook.com
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Describe image when Object located beyond C
• Real or Virtual? • Real• Erect or Inverted? • Inverted• Same size, Enlarged or Reduced?• Reduced• Location?• Between f and C
Concave Mirror
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Concave Mirror with the Object located
beyond C
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Light rays that travel parallel to the principle axis, strike the mirror, and are reflected back through
the focal point (f).
Concave Mirror
Object beyond C
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Light rays that travel through the focal point (f), strike the mirror, and are reflected back
parallel to the principle axis.
Concave Mirror
Object beyond C
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Concave Mirror
Object beyond C
Image:
Real
Inverted
Smaller
Between f and C
The image is located where the reflected light rays intersect
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Concave Mirror with the Object located at C
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Concave Mirror
Object at C
Light rays that travel parallel to the principle axis, strike the mirror, and are reflected back through
the focal point (f).
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Concave Mirror
Object at C
Light rays that travel through the focal point (f), strike the mirror, and are reflected back
parallel to the principle axis.
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Concave Mirror
Object at C
Image:
Real
Inverted
Same Size
At C
The image is located where the reflected light rays intersect
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Concave Mirror with the Object located between f and C
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Describe image when Object located between f and C
• Real or Virtual? • Real• Erect or Inverted? • Inverted• Same size, Enlarged or Reduced?• Larger• Location?• Beyond C
Concave Mirror
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Concave Mirror
Object between f and C
Light rays that travel parallel to the principle axis, strike the mirror, and are reflected back through
the focal point (f).
f C
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Concave Mirror
Object between f and C
Light rays that travel through the focal point (f), strike the mirror, and are reflected back
parallel to the principle axis.
f C
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Concave Mirror
Object between f and C
Image:
Real
Inverted
Larger
Beyond C
The image is located where the reflected light rays intersect
f C
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Concave Mirror with the Object located at f
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Concave Mirror
Object at f
Light rays that pass through the center of curvature hit the mirror and are reflected back
along the same path.
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Concave Mirror
Object at f
Light rays that travel parallel to the principle axis, strike the mirror, and are reflected back through
the focal point (f).
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Concave Mirror
Object at f
No image is formed.
All reflected light rays are parallel and do not cross
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Concave Mirror with the Object located between f and the
mirror
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Describe image when Object located between f and mirror
• Real or Virtual? • Virtual• Erect or Inverted? • Erect• Same size, Enlarged or Reduced?• Larger• Location?• Further away, behind mirror
Concave Mirror
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Concave Mirror
Object between f and the mirror
Light rays that travel through the focal point (f), strike the mirror, and are reflected back
parallel to the principle axis.
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Light rays that travel parallel to the principle axis, strike the mirror, and are reflected back through
the focal point (f).
Concave Mirror
Object between f and the mirror
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Concave Mirror
Object between f and the mirror
Image:
Virtual
Upright
Larger
Further away
The image is located where the reflected light rays intersect
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Locating images in convex mirrors
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Convex Mirror with the Object located
anywhere in front of the mirror
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Light rays that travel parallel to the principle axis, strike the mirror, and are reflected back through
the focal point (f). f is negative.
Convex Mirror
Object located anywhere
f C
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Light rays that travel through (toward) the focal point (f), strike the mirror, and are
reflected back parallel to the principle axis.
Convex Mirror
Object located anywhere
f C
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Convex Mirror
Object located anywhere
Image:
Virtual
Upright
Smaller
Behind mirror, inside f di is negative
The image is located where the reflected light rays intersect
f C
THE MIRROR EQUATION
The mirror equation can be used to locate the image:
1 1 1
d d fo i
Mh
h
d
di
o
i
o
The ratio M is called the magnification, ho is the object’s size and hi is the image size.
Where do is the object’s distance, di is the image distance and f is the focal length.
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• do = distance between object and mirror/lens
• di = distance between image and mirror/lens
• ho = height of object
• hi = height of image
• m = optical enlargement of an object, ratio of size of image to size of object
Example Suppose you place a 5.0 cm tall pencil in front of a concave mirror. The mirror has a focal length of 24 cm. The pencil forms an image that appears to be at the same position as the spring, but the image is inverted.a. Where did you place the pencil?
ho = 5 cm
f = 24 cmdo = di
1 1 1
d d fo o
do = 2f
= 2(24cm) = 48 cm
1 1 1
d d fo i
So…
2do
=1f
b. How tall is the pencil’s image?
ho = 5 cmh
h
d
di
o
i
o
hi = -ho
= - 5 cm
hi
h0
= -1
Example Suppose you are 19 cm in front of the bell of your friend’s trumpet and you see your image at 14 cm. Treating the trumpet’s bell as a concave mirror, what would be its focal length and radius of curvature?
do = 19 cm
di = 14 cm
1 1 1
d d fo i
f = 8.06 cm
R = 2f = 2(8.06cm) = 16.12 cm
119cm
= 1f
114cm
+
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• What type of mirror could have created the image shown above?– A. Plane– B. Concave– C. Convex
OriginalImage
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• Where would the object need to be placed to create this image?– A. At C– B. Between f and C– C. Beyond C– D. Between f and the mirror
Originalimage
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• Where would this image form?– A. At C– B. Between f and C– C. Beyond C– D. Between f and the mirror
Originalimage
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• If the focus of a convex mirror is 60 cm from the mirror, what is the radius of curvature?
• A. 120 cm
• B. -120 cm
• C. 30 cm
• D. -30 cm
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Convex mirror diagram
• An object is 5 meters in front of a convex mirror. The object is 1.5 meters tall. The mirror has a radius curvature of 12 meters.
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• A man 2 m tall stands 10 m in front of a convex mirror which has a radius of curvature of 5 m. How tall is the image?
• A. 0.4 m• B. -0.7 m• C. 0.7 m• D. 2 m• Hint: must calculate to di determine hi
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• A concave mirror of radius 60 cm is placed so that a luminous object is 35 cm in front of the mirror. Where does the image form?
• A. Beyond C
• B. Behind mirror
• C. Between f and C
• a. 0.0048 cm
• b. 210 cm
• c. -0.012 cm
• d. -84 cm
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• Get graph paper
• Starboard
• Documents
• Templates
• Linear Paper 207
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Draw the following ray diagramEx 1
• Concave mirror• Center of curvature of mirror 10 cm• Object 15 cm from mirror• Object height is 2 cm• Where is the image and how tall is it?• Did the light rays converge at the image?• Is it real or virtual?
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• di ~ 13.7cm in front of mirror
• hi = 1cm reduced and inverted -1cm
• Negative indicates inverted
• Rays converge, inverted real image
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Draw the following ray diagramEx 2
• Concave mirror• Focal length 5cm• Object 3 cm from mirror• Object height is 2cm• Where is the image and how tall is it?• Did the light rays converge at the image?• Is it real or virtual?
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• di ~ 4 cm behind mirror -4cm
• The negative indicates image is behind the mirroe
• hi = 3.5cm enlarged
• Rays do not converge, erect virtual image
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Draw the following ray diagram
• Convex mirror• Center of curvature of mirror -10 cm• Object 15 cm from mirror (why is this positive?)• Object height is 3 cm• Where is the image and how tall is it?• Did the light rays converge at the image?• Is it real or virtual?
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• di ~ -3.5cm
• The negative indicates image is behind the mirror
• hi = 1 cm reduced
• Rays do not converge, erect virtual image
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• Where does object have to be to produce a virtual image?
• Between F and mirror• Where does object have to be to produce a
real image? • Beyond F• Were the real image always reduced?• No
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Object Location
Real or Virtual
Erect or Inverted
Size
Plane Mirror
Concave Mirror
Convex Mirror
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Diagram from mirror lab
•A curved mirror has a geometric center or vertex A•The center of curvature or radius C•The focal length f of the mirror is half the radius
f R1
2