it’s what we see…

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