1. A “Visual” Review
Lyzinski Physics

2. Light? Where does it come from?
It comes from moving electrons
- different energy levels in an atom
- when light jumps UP, it absorbs energy (usually in the
form of heat)
- when light jumps DOWN, it emits energy in the form of
light.
- the color of the light depends on the size of the jump.
Moving electrons set up a changing electric field that also induces a changing magnetic field.
 Electromagnetic Waves!!!!

3. Light? What is it (what is it like)?
It is both wave-like AND particle-like.
It is a transverse, electromagnetic wave
- Transverse (light) vs. longitudinal (sound)
- Electromagnetic wave
No medium needed
It travels at the speed of light (c = 3E8 m/s)
It travels in straight lines  rectilinear propagation
It travels in rays (infinitely thin)
The approximate speed of light in a vacuum (or in air)

4. General Equation: works for sound, water, slinkies, light, etc.
The Wave Equation
General Equation: works for sound, water, slinkies, light, etc.
Velocity Frequency Wavelength
For light,
Increase l, decrease f.
Decrease l, increase f.
Light Equation

5. The Electromagnetic Spectrum
Radio Micro Infra ROYGBIV Ultraviolet X Gamma
AM FM

6. AM vs. FM 535-1605 kHz 88-108 MHz Lower frequency Higher frequency
Longer wavelength
Higher frequency
Shorter wavelength
kHz = kilohertz = 103 Hz
MHz = megahertz = 106 Hz

7. Some Helpful Applets
Applets showing longitudinal AND transverse waves.
Applet explaining how a moving electron (jumping and falling in energy level) produces a wave.
Applets showing a 3D electromagnetic wave.

8. Plane Reflectors
Normal
Incident Ray
Reflected Ray
Rule #1: The angle of Incidence equals the angle of reflection.
Rule #2: The normal, incident ray, and reflected ray all lie in the same plane.

9. Drawing PLANE MIRROR Ray Diagrams
Draw two incident rays from a point.
Find the intersection of the two reflected rays.
Repeat for every point on the object B’ C’ C B
mirror

10. Light “Caves in” on the Focus CONCAVE (CONVERGING)
Spherical Mirrors
Light “Caves in” on the Focus CONCAVE (CONVERGING)
Notice that qi = qr C
Focus
Center of Curvature
Principal Axis F
f = focal length
R = radius of curvature

11. Spherical Mirrors vs. Parabolic Mirrors
Large spherical mirrors have an avoidable issue.
…..using mirrors that are PARABOLIC, instead of spherical
…..using mirrors whose width (w) is smaller than its radius of curvature (R). OR R w
Near the edges, reflected rays might not reflect through the focus.
This is known as SPHERICAL ABBERATION .
It can be corrected by…..

12. Again, Notice that qi = qr
Spherical Mirrors
CONVEX (DIVERGING) C F
Principal Axis
Again, Notice that qi = qr
Center of Curvature f
“Virtual” Focus R

13. Image Formation What does your eye see??? Object Image Plane Mirror
Cone of rays seen by the human eye
Object Image
Virtual
(cannot be formed on a screen)
Plane Mirror

14. Characteristics of Images
TYPE
Real
Virtual VS
Can be formed on a screen Can NOT be formed on a screen
Upright
ATTITUDE
Inverted VS
or “Orientation”
Larger
Same size
Smaller

15. Image Formation (continued)
A screen placed here will have a focused image on it.
A screen placed here will have a “fuzzy”, unfocused image on it.
In Spherical, CONCAVE mirrors, a clear image is formed where all the reflected rays emitted from any single point on the object intersect.

16. How do you locate the image in a Spherical Mirror Situation.
Pick a point on the object (usually the one furthest from the principal axis), and then draw 2 intersecting rays that obey the following rules:
Any ray parallel to the principal axis is reflected through the focus.
2. Any ray through the focus is reflected parallel to the principal axis.
Any ray through the center of curvature is reflected back along the
incident ray (back along itself)

17. Concave Mirrors “OUTSIDE“ the focus C F
Moving towards the focus, the image is REAL, inverted, and gets larger.

18. Concave Mirrors “ON” the focus C F
When an object is at the focus, it doesn’t have an image.

19. Concave Mirrors “INSIDE” the focus C F
Moving towards the mirror, the image is VIRTUAL, UPRIGHT, and gets smaller (although the image is still larger than the object itself).

20. Note: All images are in front of the virtual focus.
Convex Mirrors
Note: All images are in front of the virtual focus.
F C
When an object gets closer to the mirror, its image is VIRTUAL, UPRIGHT, and keeps getting smaller (and the images are always smaller than the object).

21. Wanna play with mirrors?
try an applet at …..

22. Mathematically locating an image
All distances are measured from the mirror’s vertex
Distances are POSITIVE for REAL images/objects
Mirror
Equation
Distances are NEGATIVE for VIRTUAL images/objects
Heights are positive when measured upward and negative when measured downward.
M is the magnification.
Magnification
Equation

23. A few Helpful tips to using the equations.
Always write out a list of do, di, ho, hi, f, and M first.
Using knowledge of the type of mirror you have and where the object is placed, make sure the SIGNS are correct on your variables before plugging the variables into the equations.
ALWAYS check your answers to makes sure that they 1) match your drawing 2) have signs that make sense 3) have numbers that make sense.

24. Example
A converging mirror is used to take a 4 meter tall object and create a 2 meter tall image of it that is formed on a screen. If the object is 3 meters from the mirror, find the mirror’s focal length, the image distance, and the magnification.
hi = -2m (negative because it must be upside down, since real images in a
converging mirror are always inverted).
ho = 4m
do = 3m
f = + ___ (since it’s a concave, converging mirror)
di = +___ (since it’s real)
-1 < M < 0 (since its inverted and smaller)

25. Another Example
A mirror is used to create a small, upright image. If the radius of curvature of the mirror is 40 cm, and if the image is 4 times smaller than the object, how far in front of the mirror has the object been placed?
THE mirror must be diverging since only convex mirrors can create smaller, upright images! Therefore, f = -20 cm.
Also, M = +1/2 (since the image is half the size of the object).
You have to use a substitution method on this problem, yielding:
di = - ___ (since the image is virtual)
do = + ___ (since the object is real)

26. Concave mirrors Convex mirrors Can make small objects appear larger
Make-up mirrors, shaving mirrors
Convex mirrors
Can make large objects appear smaller (see a WIDE view)
Security mirrors, Driveway mirrors, Car door mirrors

27. Uses for PARABOLIC mirrors (in case you were wondering )
At solar power plants, parabolic “troughs” (as they’re called) are used to focus light onto a fluid carrying pipe, thus heating the fluid and producing useable energy.
Fluid filled pipe being heated
Parabolic trough