1. Light and Reflection
Can you see me?

2. 14-1
EM waves as we discussed before is the classification that light falls under;
White light is all light of the visible spectrum
Red, orange, yellow, green, blue, and violet
Not all light is visible to the human eye
Xrays, microwaves, and radiowaves have the same properties as visible light but we can’t see them. They are still considered EM waves

3. EM waves

4. EM waves depend on λ ƒ
Classic EM waves are considered oscillating magnetic fields and electric fields
Transverse waves (?)
Look at pink sheet to determine how wavelength and frequency affect light

5. c=λƒ V? All EM waves move at the speed of light
Speed of light (C) is 3.00 x 108 m/s
Barely changes
Equation for speed of light
c=λƒ

6. Problem
The AM radio band Mr. Kuehn listens to is WCCO x 105 Hz and 9.37 MHz for FM. What are the wavelengths for these frequencies?

7. Problem
The brightest light humans can see is 560 nm in wavelength, what is the frequency of this wavelength?
Answer 5.4 x 1014 Hz

8. Light travels as wave fronts

9. Brightness
Brightness decreases by the square of the distance from the source.
As you move away from a light source, the light wave front spreads out more and distributes the energy over a greater area.
Each area receives less energy when further away

10. Inverse square law

11. Reflection

12. Reflection
Light travels through any uniform medium or absence of medium in straight lines
If light comes in contact with different medium, some of the light will be absorbed and some reflected.
Reflection is a change of direction of light.
Even good mirrors can only reflect 90% of light

13. Types of Reflection
Diffused reflection: reflections in many directions off a rough uneven surface
Specular Reflection is off a perfect smooth surface and all reflection is in one direction

14. Incoming and reflected angles
Angle of incidence = angle of reflection
θ=θ’
Angle of incoming= angle of reflected from Normal

15. Flat Mirrors
When images reflect off of flat mirrors, the object appears to be behind the mirror.
The distance the image appears to be behind the mirror, “q” and the objects distance from the flat mirror, “p”, are EQUAL!
The image behind the mirror is called the virtual image

16. Image locations Image locations can be located with ray diagrams
Ray diagrams can be drawn to locate images using p, q, θ and θ’.

17. Steps
1)Draw object and image at respective p and q from a parallel mirror making sure their heights are the same
2) Draw a perpendicular “ray” of light. Once the ray passes through the mirror, make a dashed line.
3) Draw an angled “ray” including θ measurements. Draw the same “ray” for the image.

18. Flat Mirrors
p = q
θ=θ’
h=h’
Left Right reversal happens

19. Curved Mirrors

20. Curved Mirrors Curved Mirrors reflect light too Concave Mirror
Convex Mirror
Factors that affect image:
Amount of curve =radius of curve “r”
Center of curvature “c”
Draw light left to right.

21. Real or virtual
REAL- It usually appears INVERTED (depends on the type of mirror e.g convex, concave) It can be OBTAINED ON A SCREEN In case of mirror, the image lies in front of the reflecting surface. In case of lens, the image lies on the other side of the object. The light rays meet at a focal point in front of the mirror
VIRTUAL- It usually appears ERECT It CANNOT be obtained on a screen In case of a mirror, the image lies behind the mirror In case of lens, the image lies on the same side of the object The light rays meet at a focal point behind the mirror

22. Concave
Real images are images formed when rays of light actually intersect at a single point
To find image location
1/p + 1/q = 2/R
p = object distance
q= image distance
R= radius of curvature
1/p + 1/q = 1/f
F= focal length

23. Magnification Magnification for mirrors M=h’/h = -q/p Signs
=image height/ object height
= -image distance/object distance
M=h’/h = -q/p
Signs
+ for upright images virtual images
- for inverted real images

24. Ray diagrams for mirrors
Rays
Object to mirror
Mirror to image 1
Parallel to axis
Through F 2 3
Through Center of curvature “C”
Back along itself through “C”

25. Drawing

26. Example
A concave mirror has a focal length of 10.0 cm. Locate the image of a pencil that is place upright 30.0 cm from the mirror. Find the magnification of the images. Draw a ray diagram
q = 15 cm
M= -.50

27. Example 2
If you had a large concave telescope with a focal length of 2.5 m. Where would you place an object in front of the mirror in order to form an image at a distance of 3.75 m? What would the magnification be? If the image height were 6.0 cm, what would the object height be?
P= 7.50 m M=
h= 12 cm

28. Convex Mirrors Convex mirrors curve out. Same rules apply Rays
Object to mirror
Mirror to image 1
Parallel to axis
Through F 2 3
Through Center of curvature “C”
Back along itself through “C”

29. Symbol
Situation
sign p
Object in front of mirror + q
Image in front of mirror (real)
Image is behind mirror (virtual) -
R,f
C in front (convex)
C in back (concave)
Flat mirror
infinite h'
Image above axis
Image is below

30. Example 539
An upright object is placed in front of a convex mirror with a focal length of 8.00 cm. An upright image 2.5 cm tall is formed 4.44 cm behind mirror. Find the position of the object, magnification and height of the object.
P=10.0 cm
M= 0.444
H=5.63 cm

31. Example 2
The largest jelly fish every caught has tentacles 36 m long. Supposed the jelly fish is located in front of a convex mirror 36.0 m away. If the mirror had a focal length of 12.0 m, how far from the mirror is the image? What is the h’? m
M= .250
H’= 9.001