1. Electromagnetism and Energy
Causes and effects of
static and dynamic
electric & magnetic fields
Maxwell equations yield
electromagnetic waves
Electromagnetic energy
Thermal energy:
heating, melting, boiling,
Potential energy:
electrostatic, gravitational
Kinetic energy
Bernoulli equation

2. Electrodynamics Giancoli Ch.21-29 Physics of Astronomy, winter week 6
Star Date
HW: finish CO 3.6, magnitudes
Overview of EM & Maxwell’s eqns
Minilectures
Derive EM wave equation and c
Next week: write Interim Research Planning Report
Boas Ch.4: partial differentiation (1-6)
Week 8: Modern physics + CO Ch.5: Interaction of light and matter

3. Causes and effects of E Gauss: E fields diverge from charges
Lorentz: E fields can move charges
F = q E

4. Causes and effects of B Ampere: B fields curl around currents
Lorentz: B fields can bend moving charges
F = q v x X = IL x B

5. Changing fields create new fields!
Faraday: Changing magnetic flux induces circulating electric field
Guess what a changing E field induces?

6. Changing E field creates B field!
Current piles charge onto capacitor
Magnetic field doesn’t stop
Changing
 “displacement current”

7. Maxwell’s equations

8. Maxwell eqns  electromagnetic waves
Consider waves traveling in the x direction with frequency f= w/2p
and wavelength l= 2p/k
E(x,t)=E0 sin (kx-wt) and
B(x,t)=B0 sin (kx-wt)
Do these solve Faraday and Ampere’s laws?

9. Faraday + Ampere

10. Sub in: E=E0 sin (kx-wt) and B=B0 sin (kx-wt)

11. Speed of Maxwellian waves?
Faraday
B0/E0 = 1/v
Ampere
B0/E0 = m0 e0 v
Eliminate B0/E0 and solve for v:
e0 = 8.85 x C2 N/m2
m0 = 4 p x 10-7 Tm/A

12. Maxwell equations  Light
E(x,t)=E0 sin (kx-wt) and B(x,t)=B0 sin (kx-wt)
solve Faraday’s and Ampere’s laws.
Electromagnetic waves in vacuum have speed c and energy/volume = 1/2 e0 E2 = B2 /(2m0 )