1. Chapter 24 Electromagnetic waves Lecture 11 April 26, 2005

2. My equations: And the Lorentz force from E and B on A charges q:

3. describe all electric and magnetic phenomena and LIGHT Demo 1 - 200 MHz

4. Which is not one of Maxwell’s equations? 1234512345

5. Which is true? Maxwell’s equations 1.Have been superseded by relativity. 2.Were all anticipated by experiment. 3.May be derived from pure thought. 4.Are mathematical descriptions of empirical fact. 5.Are irrelevant to modern physics.

6. Electromagnetic waves If we look at Maxwell’s eqns where there are no charges or currents - after a bit of math we will get… Units of 1/speed 2

7. This is one way to look. See Chapter 24.3

8. Suppose we start with a sine wave electric field in the x direction traveling in the z direction: The Ampere-Maxwell law says Path of integral

9. Then the Faraday law of induction says This can only be true if Path of integral Which implies

10. The speed of the waves is Units of 1/speed 2 Light is an electromagentic wave. It is described by Maxwell’s equations. Electricity, magnetism and optics are different aspects of the same theory.

11. This is in the vacuum. In a medium of dielectric constant  and magnetic permeability  the speed of light is

12. Electromagnetic waves are transverse ^ ^ y Demo 2 – 10 GHz

13. In an electromagnetic wave, the directions of the electric and magnetic fields must be 1.Opposite. 2.Parallel. 3.Perpendicular. 4.Sinusoidal. 5.Symmetric.

14. In an electromagnetic wave, the fact that the electric and magnetic fields are perpendicular to the direction of propagation of the wave means that the wave is 1.Perverse. 2.Inverse. 3.Reverse. 4.Transverse. 5.Obverse.

15. Electromagnetic spectrum All these are the same beast…differing only in wavelength Absorbed by water (microwave oven) Permeate the universe Heat Strongest solar light (hence the evolutionary preference) Harmful in high dosage Absorber by ozone in the upper atmosphere Can punch through organic material Causes cancer in high doses Controlled doses kill cancer cells Positronium annihilation gamma ray laser! FCC-Free communication band