1. Phy2005 Applied Physics II Spring 2016 Announcements:
Test 2 Wednesday, March 23 covers chs , sections listed in
syllabus + all material covered in class
2 practice tests posted on course Tests page
Review session in class March 21 in class + March 21 6pm NPB 2205

2. Last time

3. The Superhero in Artificial Intelligence
Google DeepMind AlphaGo beat a Go master (Lee, Se-dol, world ranking #2)
4 times out of 5 matches.

4. Last time θ
I = I0cos2θ
Intensity after polaroid
Intensity before polaroid
For unpolarized light, a polaroid sheet reduces its intensity
to half (sunglasses).

5. Clicker Quiz Time Log in your remote! ACADEMIC HONESTY
Each student is expected to hold himself/herself to a high standard of academic honesty. Under the UF academic honesty policy. Violations of this policy will be dealt with severely. There will be no warnings or exceptions.
Log in your remote!

6. Q1 There are two light sources
Q1 There are two light sources. One is unpolarized and the other is linearly polarized. When you look at these light sources through a polaroid while rotating the polaroid axis 360 degree. What do you expect to observe?
For both you do not see any changes in the intensity during the full rotation.
The intensity varies during the full rotation for both light source.
One sees the intensity variation only for the unpolarized light.
One sees the intensity variation only for the polarized light.

7. Q2 A polaroid is placed at a 45o angle with respect to a linearly polarized light beam incident on it. The transmitted beam is then passed through a second polaroid at 45o with respect to the first polaroid. What fraction of the initial lightlight intensity is perpendicular to the initial beam?
1/3 1
1/2
1/4
Remember ?
I = I0cos2θ

8. Starting from A, make one touch at the wall and finish at B.
Which path takes the shortest time?
θ θ
x A
x B
Principle of shortest time determines: relection, refraction

9. Reflection and Mirrors
qi = qr qi qr
Law of reflection
Specular Reflection
Diffuse Reflection

10. Image forms at the point where the light rays converge.
When we talk about an image, start from an ideal point light source.
Every object can be constructed as a collection of point light sources.
VIRTUAL
IMAGE q p
Image forms at the point where the light rays converge.
When real light rays converge  Real Image
When imaginary extension of L.R. converge  Virtual Image
Only real image can be viewed on screen placed at the spot.

11. How about left-right? Let’s checkp q
IMAGE
VIRTUAL
For plane mirror: p = q
How about left-right? Let’s check
From now on p: distance to the object
q: distance to the image

12. Parallel light rays: your point light source is very far away.
Spherical Mirror
R: radius of curvature
focal Point
f: focal length = R/2
Optical axis
concave
convex
Parallel light rays: your point light source is very far away.
Focal point:
(i) Parallel incident rays converge after reflection
(ii) image of a far away point light source forms
(iii) On the optical axis

13. Spherical Aberration Reflected rays do not converge:
Not well-defined focal point
not clear image
Spherical Aberration
f = R/2 holds strictly for a very
narrow beam.
Parabolic mirror can fix this problem.

14. Spherical Aberration:
some mirrors were ground wrong by
1/50th of human hair thickness.

16. Case 1: p > R p f q
P > q
Real Image

17. Case 2: p = R
p = q
Real Image

18. Case 3: f < p < R
p < q
Real Image

19. Case 4: p = f
q = infinite

20. Case 5: p < f
q < 0
Virtual Image

21. For a small object, f = R/2 (spherical mirror)
Mirror Equation
1/p + 1/q = 1/f
For a small object, f = R/2 (spherical mirror)
1/p + 1/q = 2/R
Alert!!
Be careful with the sign!!
Negative means that it is inside the mirror!!
p can never be negative (why?)
negative q means the image is formed inside the mirror
VIRTUAL
How about f?

22. Focal point inside the mirror
For a concave mirror: f > 0
Focal point inside the mirror
f < 0
1/p + 1/q = 1/f < 0 : q should be negative.

23. All images formed by a convex mirror are VIRTUAL.
1/p + 1/q = 1/f < 0 : q should be negative.
All images formed by a convex mirror are VIRTUAL.
Magnification, M = -q/p
Negative M means that the image is upside-down.
For real images, q > 0 and M < 0 (upside-down).

24. Ex. 26.1 An object is placed at the center of curvature of a
Mirror. Where is the image formed? Describe the image?
1/p + 1/q = 1/f f = R/2
Object is at the center: p = R
1/q = 1/f – 1/p
= 2/R – 1/R
= 1/R
q = R > 0 (Real Image)
M = -q/p = -R/R = -1
No magnification but upside-down

25. Up-right or Upside-down
Ex A concave mirror has a 30 cm radius of curvature.
If an object is placed 10 cm from the mirror, where will the
image be found?
f = R/2 = 15 cm, p = 10 cm
1/p + 1/q = 1/f  1/10 + 1/q = 1/15
3/30 + 1/q = 2/30
1/q = -1/30
q = -30 cm
Case 5: p < f
Real or Virtual
Magnified or Reduced
Up-right or Upside-down
q < 0
M = -q/p = 3

26. Q. An upright image that is one-half as large as an object is
needed to be formed on a screen in a laboratory experiment
using only a concave mirror with 1 m radius of curvature.
If you can make this image, I will give you $10. If you can’t
you should pay me $10. Deal or no deal? Why?
1/p + 1/q = 1/f = 2/R > 0
M = -q/p = ½ > 0
should be a real image: q > 0
M = -q/p cannot be positive, if q > 0.
No deal!!!