it’s what we see…
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It’s what we see…. Light Speed. light around the earth 300,000,000 m/s 3 x 10 8 m/s. Light Speed. Just over a second from the moon. Light Speed. 8 minutes from the sun. Light Speed. Light Speed. 4.2 years from Alpha Centauri! (second nearest star). - PowerPoint PPT PresentationTRANSCRIPT
It’s what we see…
Light Speed
•light around the earth
•300,000,000 m/s
•3 x 108 m/s
Light Speed
•Just over a second from the moon
Light Speed
•8 minutes from the sun
Light Speed
•4.2 years from Alpha Centauri! (second nearest star)
•4.2 years from Alpha Centauri! (second nearest star)
Light Speed
Lightyear
•170, 000 lightyears away•How many years ago did it occur?
How far light travels in 1 year
Plane Mirrors: The Flat Mirrors
Plane Mirrors
•Incident ray hits the mirror
•Reflected ray is the ray that bounces off
•The Normal is the perpendicular line from mirror
3 Laws of Reflection
i = r di to mirror = do to mirror Apparent path
of light = Actual path of light
Draw the Reflected Ray
54° 54°
1. Draw the normal
2. Measure the incident angle
3. Draw the reflected ray
Let practice! Turn to page 15
Work together to solve #1 and #2
#1b. Headlight on a dry road
3 Laws of Reflection
i = r di to mirror = do to mirror Apparent path
of light = Actual path of light
Reflection
Virtual Image of the nose
• To find an image: extend the reflected ray behind the mirror.
• The image is formed where the rays intersect.
do di
do= object distance di= image distance
mirror
Image
mirrorApparent path of
light
Actual path of light?
Object
Length of Actual Path of light =
Length of Apparent path of light
Lab part 2: Parallaxreal screw (behind mirror)
image of screw
mirror• Parallax can be
used to find image location• Parallax makes
objects appear to move when not in the same place• Try it
Parallax
• Move head to the side• If the image and
real screw separate, then not at same place• Try it
mirror
Parallax
• If the two move together, they are at same place• Try it
mirror
Now, to the LabPart II (pg
11)
Common Lab ShortfallsUse Full SentencesNon-Example:
4.2cm and 4.5 cm. 5%
The distance from the object to the mirror is __ cm and the distance from the mirror to the image is __cm. The percent
difference is __% which indicates ___________________.
What is 4.2cm???Example of a great response:
Part 2: Compare using the Percent difference
#1. Headlight on a dry road
Headlight on a dry road
1. Diffuse Reflectors
#3. Find the Object
Find the Object
Image to eye
14.5 cm
Object14.5 cm
Apparent path of light
Actual path of light
4. Yourself in a Mirror
Minimum height of mirror?
Tip for #4
Work backwards! Where do the rays need to reach to let everything be seen?
Tip for #6In order to focus you camera you
must know the distance between the camera and the image
Problem 9
mirror
object
mirror
3.0 m
2.0 m2.0
m1.0 m
1.0 m
A man is standing between 2 parallel mirrors looking
to the left. How far
away from the person are the first
three images he
sees?
Problem 6mirror
2.0 m
2.0 m
4.5 m
4.5 m
object
image
Problem 7: 25° with the surface of the
mirror… ?
Mirror25°
normal
θ
θ = incident angle
90° = θ + 25°90° – 25° = θ
65° = θ
But what is the question is asking?
Curved Mirrors
Curved Mirror Vocab
C = radius of the sphere the mirror was made from
f = point at which rays convergeF = length of the mirror to f (focal length) f = C/2
Concave mirrorC f
Center of curvature
= Focal point
Image TypesVirtual images are formed by
diverging light rays (example: behind a plane mirror)
Real images are formed by converging light rays
Real or Virtual?
Vocab
WordPicture that reminds you of definition
DefinitionWord or words that remind you of definition
Sentence using word
Converge
Come together from different directions to eventually meet
• Come together• Cross
• Eventually meet
The students will converge in the cafeteria
Vocab
WordPicture that reminds you of definition
DefinitionWord or words that remind you of definition
Sentence using word
Diverge
Separate and go in different directions
• Separate• Grow apart • Turn away
Monkeys and Humans diverged from a common ancestor
Real vs Virtual Images
Concave MirrorImage in frontUse a Card to
see!
Light rays converge
Image is Real
Real vs. Virtual Images
Concave Mirror
Image behind mirror
Appears to converge
Image is virtual
Real Or Virtual ?
Image behind mirror
Appears to converge
Image is virtual
Real Or Virtual ?
Image in front of a curved mirror
Appears to diverge
Image is real
Let practice! Turn to page 23
Skip pg 24
Skip question 3 on page 27
Normals to the surface have already been drawn as dashed lines.
Concave Mirrors
C f
through the focal point!Incoming Parallel rays reflect:
Concave Mirrors
C f
parallel!Rays through (or from) f reflect:
Concave Mirrors
C f
back through C!Rays through C reflect:
Convex Mirrors
C f
away from focal point!Incoming parallel rays reflect:
Note: Only the red lines are used to locate the image
Convex Mirrors
C f
parallel!Rays towards focal point reflect:
Convex Mirrors
C f
back away from C!Rays towards C reflect:
Choose easiest paths
(Only need 2) Use 3rd to “check”
image
The Image is between the Principle axis & the intersection
Finding the ImageDraw ray pathsIdentify
Characteristics
Beyond C
largerinverted
Real
R = Region S = Size O = Orientation T = Type of Image
Now Go Make Your Own!
Pages 30-33
Answers pg 31
R = Region S = Size O = Orientation T = Type of Image
Image Characteristics
Concave and Convex
Concave: (pg 32)Object at center of Curvature
Concave (pg 32)Object between C and F
Concave (pg 32)Object between F and Mirror
Prior Knowledge: Lab 2
Virtual Image of the nose
do di
do= object distance di= image distance
+ -
Lab 2
Measure object distance from the filament
Advice
Record the object size, orientation & image position
Mark & number all 11 object and image distances on your paper! (skip recording the object and image distances, you
can measure those later)
Look at the table on page 37
Your data tableImage Size: larger, smaller, or
same? Image Orientation: upright or
inverted? Image Position; behind mirror
(distance will be negative) OR between mirror and object, at object, or beyond object?+ -
How do you calculate the focal length of a curved
mirror?
1/f =1/do +1/dif = dodi / (do + di)
Lab Corrections
Earn back up to ½ the points you lost
Corrections should be done in colored pen/pencil OR on a separate piece of paper
Turn corrections into the regrade folder
The Lab: Part 1
Image
do di
do= object distance di= image distance
Lab Corrections
Due 1 week from the day it was due (Tuesday Tuesday)
Correct your lab and write a note to the front telling me:
1. what you corrected 2. your original mistake
NOTE: You can not earn points back by labeling the image
Use your Ray diagrams on page 30-33 to fill out
the table on pg. 39 Type of mirror
Object position
Image
Position Relative Size
Orientation
Type
concave
Mirror to focus
Center of Curvature
At C Same Inverted Real
Pg 39 Convex mirror
Position: Size: Larger / Smaller / SameOrientation: Upright / InvertedType: Real / Virtual
Convex mirrorpg 39
Position: Size: Larger / Smaller / SameOrientation: Upright / InvertedType: Real / Virtual
VirtualUprightSmaller
Behind the mirror
Mirror EquationsSolving for f
Mirror EquationsMagnificationReally 3 different equations
Mirror Equations
ImageDistance
FocalLength
Positive
negative
Concave mirrorsConvex mirrors
In front of mirror
Behind mirror
object
+ -
Prior Knowledge: Lab 2
Virtual Image of the nose
do di
do= object distance di= image distance
+ -
Let’s try some examples!
1.6 A girl is using a concave makeup mirror to get ready for the prom and is 27 cm in front of the mirror. The image is 65 cm behind the mirror.a. Find the focal length of the mirrorLet’s go over how to approach word
problems…
Solving Word Problems: GUESS
1. List your Given information (numbers you can use in eqns) make sure to label them with a
variable sometimes this includes a picture
1.6 A girl is using a concave makeup mirror to get ready for the prom and is 27 cm in front of the mirror. The image is 65 cm behind the mirror.a. Find the focal length of the mirror Given:
Solving Word Problems: GUESS
2. List your Unknown this is what you are solving for!
1.6 A girl is using a concave makeup mirror to get ready for the prom and is 27 cm in front of the mirror. The image is 65 cm behind the mirror.a. Find the focal length of the mirror Given:
f = ?
Solving Word Problems: GUESS
3. Write out the Equation you will use Write it the way you will use it
A girl is using a concave makeup mirror to get ready for the prom and is 27 cm in front of the mirror. The image is 65 cm behind the mirror.
a. Find the focal length of the mirror Given:
f = ?
Solving Word Problems: GUESS
4. Substitute: Plug your numbers into the equation
Do not forget your units!
A girl is using a concave makeup mirror to get ready for the prom and is 27 cm in front of the mirror. The image is 65 cm behind the mirror.
a. Find the focal length of the mirror Given:
f = ?
Solving Word Problems: GUESS
5. Solve: Calculate and write your answer!
Box it!
A girl is using a concave makeup mirror to get ready for the prom and is 27 cm in front of the mirror. The image is 65 cm behind the mirror.
a. Find the focal length of the mirror Given:
f = ?
A girl is using a concave makeup mirror to get ready for the prom and is 27 cm in front of the mirror. The image is 65 cm behind the mirror.
b. Find the Magnification of her image. Given:
M = ?
1.4 You are 2.0 m tall and stand 1.5 m in front of a mirror. You see an image of yourself that is upright and half your size.a. What type of image is it? Why?
Answer:Image is virtual.Why? Because image is upright.
1.4 You are 2.0 m tall and stand 1.5 m in front of a mirror. You see an image of yourself that is upright and half your size.b. What type of mirror is it? Why?
Answer:Mirror is convex.Why? Because image is smaller and virtual.
1.4 You are 2.0 m tall and stand 1.5 m in front of a mirror. You see an image of yourself that is upright and half your size.c. Find the center of curvature Given:
virtual!C = ?f = ? , di= ?
Unknown:
Equation:
Solve:
Solution:
1.4 You are 2.0 m tall and stand 1.5 m in front of a mirror. You see an image of yourself that is upright and half your size.c. Find the center of curvature
solve for f
1.4 You are 2.0 m tall and stand 1.5 m in front of a mirror. You see an image of yourself that is upright and half your size.c. Find the center of curvature
solve for C
1.7 A convex mirror has a center of curvature of 68 cm. If the image is located 22 cm from the mirror, where is the object?Given:
Unknown:
Equation:
Substitute:
Solve:
Object beyond C
f
ff
f
f
Object at C
Object between f and C
Object between f and the mirror
C
object
C
object
Image
object
object
C
C Image
Image
Image
Concave MirrorsImage type:
Image type:
Image type:
Image type:
The focal length is positive for concave mirrors
The Center of curvature is positive for concave mirrors
+ -
notes
Object anywhere
f
object
C
Image
Convex Mirrors
The focal length is negative for convex
mirrors f C
+ -
Image type:
The object distance is always positive because the object cannot go behind the mirror
Convex only produce virtual images