Last class, we found that the wave packet that we constructed from a Gaussian distribution of $k$'s centered around $k_0$ was, $$f(x) = e^{-x^2/4\sigma} e^{-ik_0x}$$ Sketch this wave packet.

## Announcements * Quiz 6 (next Friday) - Waves in conductors; details on Friday * Volunteer for Physics and Astronomy Day (April 15, 2017) * [Link to Sign-up!](https://msu.co1.qualtrics.com/jfe/form/SV_1HrDNGo5gNgMsG9)

What do y'all want to learn about after this week? 1. Potential theory and gauge (Ch. 10) 2. Accelerated charges and radiation (Ch. 11) 3. Special relativity (Ch. 12)

Fourier tells us that we can write a "pulse" by summing up sinusoidal functions: $f(x) = \int_{-\infty}^{\infty} a(k)e^{ikx}dk$ If we were to compute $f(x) = \int_{-\infty}^{\infty} a(k)e^{ik(x-vt)}dk$ where $v$ is a known constant, what would we get? 1. $f(x)$ 2. $f(vt)$ 3. $f(x-vt)$ 4. Something complicated! 5. ??? Note: * Correct Answer: C

Fourier tells us that we can write a "pulse" by summing up sinusoidal functions: $f(x) = \int_{-\infty}^{\infty} a(k)e^{ikx}dk$ If we were to compute $f(x) = \int_{-\infty}^{\infty} a(k)e^{ik(x-v(k)t)}dk$ where $v(k)$ is function, what would we get? 1. $f(x)$ 2. $f(vt)$ 3. $f(x-vt)$ 4. Something more complicated! 5. ??? Note: * Correct Answer: D