Polarization Physics 102 Professor Lee Carkner Lecture 28.

Polarization

Physics 102Professor Lee

CarknerLecture 28

PAL #27 EM Spectrum

Acceleration of lightsail craft I = Ps/4r2 = (3.9X1026)/((1.5X1011)2)

= pr = 2I/c

pr = (2)(1379)/(3X108) =

F = ma = prA a = prA/m a = (9.2X10-6)(2.25X108)/5000 =

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

Plane of Oscillation

x

y

z

y

z

E

E

Direction of Polarization

Unpolarized Light

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

Polarizing Sheet

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 I0 This is true only when the incident

light is completed unpolarized

Angle of Polarization

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 = E0 cos

I = I0 cos2

The angle can be the angle between two

adjacent polarizing sheets

Multiple Sheets

Sheet Angles

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?

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

Interstellar Polarization

Reflection Polarization

Polarization By Reflection Light reflected off of a surface is

generally polarized This is why polarized sunglasses

reduce glare

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