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Wed. Mar. 4 – Physics Lecture #34
The 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. 4
All-Campus Mentoring Day (1 – 4), Academic Fair (4 – 6)
http://www.evergreen.edu/events/mentoringdays/
Office Hours
Rachel Wed 12 – 1
Krishna Thu 2 – 3
Seth’s Tutoring Hours: see web-site
Week 20 Schedule
Mon. 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 2046
Mandatory Lab Clean-up
Physics Exam Group Reflection
Wed. Mar. 11, 9 – 1, Lab 1 2046
Calculus Exam Group Reflection
Self-Evaluation Peer Review
Quarter 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:
1. Up
3. Right
5. Into page
2. Down
4. Left
6. Out of page
P
0. No direction/zero
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?
Maxwell discovered that this electromagnetic disturbance traveled at a speed
determined by the electric and magnetic constants:
1
kE 
 9  10 9 Nm 2 /C 2
40
This speed was
v
kE

kB
0
kB 
 1  10 7 N/A 2
4
1
40
1

?
0
 0 0
4
For waves:
wave speed = (frequency) x (wavelength)
v=lf
The longest wavelength that most people can see
is 700 nm. What frequency corresponds to that
wavelength?
From WikiMedia Commons, permission granted by author Victor Blacus under a Creative Commons Attribution-Share Alike 3.0 Unported license.
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