1. Polarization Physics 102 Professor Lee Carkner Lecture 28

2. PAL #27 EM Spectrum  Acceleration of lightsail craft  I = P s /4  r 2 = (3.9X10 26 )/(  (1.5X10 11 ) 2 ) =  p r = 2I/c  p r = (2)(1379)/(3X10 8 ) =  F = ma = p r A a = p r A/m  a = (9.2X10 -6 )(2.25X10 8 )/5000 =

3. Polarization   The plane containing the E vectors is called the plane of oscillation   Most light sources are unpolarized, any given wave has a random plane of oscillation

4. Plane of Oscillation x y z y z E E

5. Direction of Polarization

6. Unpolarized Light

7. Polaroid   Polaroid is a sheet of material that will only pass through the components of the E vectors in a certain direction   If you put a horizontal Polaroid sheet on top of a vertical Polaroid sheet no light gets through

8. Polarizing Sheet

9. Polarization and Intensity   The sum of all of the y components should be equal to the sum of all of the z components  I = ½ I 0  This is true only when the incident light is completed unpolarized

10. Angle of Polarization

11. Incident Polarized Light  For polarized light incident on a sheet of Polaroid, the resultant intensity depends on the angle  between the original direction of polarization and the sheet  E = E 0 cos   I = I 0 cos 2    The angle  can be the angle between two adjacent polarizing sheets

12. Multiple Sheets

13. Sheet Angles

14. Today’s PAL  Consider unpolarized light incident on a stack of 3 polarizing sheets. The first sheet is aligned in the vertical direction. The second sheet is aligned 45 degrees from the vertical, and the third sheet is aligned in the horizontal direction. What fraction of the original intensity do you see if you look at the light after it passes through the third sheet?  What would you see if you remove the second sheet?

15. Means of Polarization   This alignment permits only the components in that direction to pass   The dust grains are partially aligned by the galactic magnetic field and so the light is partially polarized  Light can also be polarized by reflection

16. Interstellar Polarization

17. Reflection Polarization

18. Polarization By Reflection  Light reflected off of a surface is generally polarized  This is why polarized sunglasses reduce glare 

19. Next Time  Final:  Section 1, Tuesday, February 22, 9am  Section 2, Thursday, February 24, noon  Covers Chapters 21-22, 24.10 (2/3) and Chapters 13-20 (1/3)  About 15 multiple choice, 6 problems  Structured like previous tests  Practice problems online