Wed. Mar. 4 – Physics Lecture #34The Unification of Electricity and Magnetism

0. Announcements

1. Questions?

2. Electric Fields Accompany Changing Magnetic Fields, and Magnetic Fields Accompany Changing Electric Fields Electromagnetic Radiation

3. Electric Fields and Magnetic Fields are Unified

4. More Unification

(Today) Wed. Mar. 4All-Campus Mentoring Day (1 – 4), Academic Fair (4 – 6) http://www.evergreen.edu/events/mentoringdays/

Office HoursRachel Wed 12 – 1Krishna Thu 2 – 3 Seth’s Tutoring Hours: see web-site

Week 20 ScheduleMon. Mar. 9, 9 – noon, Lecture Hall 2: Physics Exam

Tue. Mar. 10, 9 – noon, LIB 1005: Calculus Exam

Tue. Mar. 10, 1 – 3:00, Lab 1 2046Mandatory Lab Clean-upPhysics Exam Group Reflection

Wed. Mar. 11, 9 – 1, Lab 1 2046Calculus Exam Group ReflectionSelf-Evaluation Peer ReviewQuarter Wrap-up

Thu. Mar. 12: Portfolios due by 9 am outside Rachel’s office Lab 2 3268

A wire loop lies in the plane of the page as shown. A point P above the loop (in the plane of the page) is indicated. Consider the following directions, and hold up as many cards as apply:

a) The current in the loop is clockwise and constant. What is the direction of the magnetic field at P?

The current in the loop now alternates (CW, then CCW, then CW, etc.)

b) What is the direction of the EM wave at the indicated point?

c) What is the polarization direction of the magnetic field portion of the EM wave at the indicated point?

d) What is the direction of the electric field associated with the EM wave at the indicated point?

How are the maximum values of the electric field and the magnetic field related?

1. Up 3. Right 5. Into page

2. Down 4. Left 6. Out of page

0. No direction/zero

P

Maxwell discovered that this electromagnetic disturbance traveled at a speed determined by the electric and magnetic constants:

This speed was ?1

4

41

000

0

B

E

kk

v

229

0

/CNm10941

Ek 270 N/A1014

Bk

From WikiMedia Commons, permission granted by author Victor Blacus under a Creative Commons Attribution-Share Alike 3.0 Unported license.

For waves:

wave speed = (frequency) x (wavelength)

v = l fThe longest wavelength that most people can see is 700 nm. What frequency corresponds to that wavelength?

Unification of Electricity & Magnetism

reveals EM waves

unifies Light & Optics w/ E&M

basis for incredible technical revolution

theoretical underpinnings sets stage for Special Relativity

experimental confirmation sets stage for Quantum Mechanics