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Lecture 9: Traveling Waves and Electromagnetic Waves
February 20, 2025
Reading Assignment
- Read: 14.1-14.2 up to “The Wave Equation” (p. 254), 29.1-29.4 (through p. 569), 29.5-29.7
- Study: Eqs 14.1-14.3; Figs 29.7, 29.10
- Skim: The rest of 29.4
Objectives
- (Continuing objective) Describe applications of the concepts of induction, waves, and light to everyday “real life” situations.
- Relate the directions and magnitudes of the electric and magnetic fields and of the propagation velocity in a harmonic plane electromagnetic wave. Explain polarization of light and how this relates to the direction of the electric field.
- Explain qualitatively how electromagnetic waves are generated by oscillating charge. From the direction and polarization of an incoming wave, determine possible directions and polarization of a re-radiated wave.
- Explain the differences between the different kinds (radio, light, etc.) of EM waves.
- Given a specific expression for a traveling transverse or longitudinal harmonic wave in sinusoidal form, determine amplitude, angular frequency, frequency, wavenumber, wavelength, period, phase shift and wavespeed.
Homework
- Friday's Assigned Problems: A27, A31, A39, A48, A91; Problem X8; Ch. 14: 13, 17; Ch. 29: 13, 23
- Monday's Hand-In Problems relevant to today's lecture: Problem X9; Ch. 14: 14, 16; Ch. 29: 20
Lecture Materials
- Click here for the Lecture overheads.
- Animation showing how an oscillating charge creates an EM wave
Videos of example problems
To see the problem statement, click on the link below. To play the video example, click on the underlined words "Video Demonstration" near the top of the page with the problem statement.- Click here for an example of the relation for the electric field in an electromagnetic wave.
Pre-Class Entertainment
- Whole Lotta Loving - Professor Longhair
- I'm Gonna Walk - The Belairs
- Three Little Birds - Bob Marley
- Say a Little Prayer - Aretha Franklin
- Let's Stay Together - Al Green
Assigned Problems Guide
- A27: quick. Think about how you interact with EM waves
- A31: medium. You need to understand re-radiation, which we will talk about in problem session
- A39: quick. Using the polaization filters in your toy kit.
- A48: medium. Practice identifying properties of an EM wave given an expression.
- A91: medium-long. Taking data from a graph to find the expression for the wave.
- X8: medium. Use the online plotting tool to look at the wave at different times and figure out the wave speed and direction.
- 14-13: quick. Use the relationship between wavelength, frequency, and wavespeed.
- 14-17: medium. Again identifying properties of a wave from an expression.
- 29-13: quick. Which way is the wave propagating? Two ways to find it.
- 29-23: quick. How are the $\vec E$, $\vec B$, and $\vec v$ directions related?