Is "The Wave" at the stadium a transverse wave or a longitudinal wave? 1. Transverse 2. Longitudinal 3. Neither Note: * Correct Answer: A
A wave on a stretched drum head is an example of a: 1. transverse wave 2. longitudinal wave 3. it's not a wave at all Note: * Correct Answer: A
## Announcements * Papers are graded and grades were sent out * Some emails bounced! * Quiz next Friday (Maxwell Ampere + Poynting Vector) * Determine the electric and magnetic field in a situation where there is a displacement current * Discuss the direction of the Poynting vector and how it relates to conservation of energy
The electric field for a plane wave is given by: $$\mathbf{E}(\mathbf{r},t) = \mathbf{E}_0e^{i(\mathbf{k}\cdot\mathbf{r} - \omega t)}$$ The vector $\mathbf{k}$ tells you: 1. The direction of the electric field vector. 2. The speed of the traveling wave. 3. The direction the plane wave moves. 4. A direction perpendicular to the direction the plane wave moves 5. None of these/MORE than one of these/??? Note: * Correct Answer: C
The electric field for a plane wave is given by: $$\mathbf{E}(\mathbf{r},t) = \mathbf{E}_0e^{i(\mathbf{k}\cdot\mathbf{r} - \omega t)}$$ Suppose $\mathbf{E}_0$ points in the $+x$ direction. Which direction is this wave moving? 1. The $x$ direction. 2. The radial ($r$) direction 3. A direction perpendicular to both $\mathbf{k}$ and $\mathbf{x}$ 4. The $\mathbf{k}$ direction 5. None of these/MORE than one of these Note: * Correct Answer: D
A wave is moving in the $+z$ direction: $$f(x, y, z, t) = Re\left[A e^{i(kz – \omega t + \delta)}\right]$$ The value of $f$ at the point $(0,0,z_0, t)$ and the point at $(x, y, z_0 , t)$ are related how? $f_1 = f (0,0,z_0 , t)$ vs. $f_2 = f(x, y, z_0 , t)$ 1. $f_1 = f_2$ always 2. $f_1 >$ or $<$ or $= f_2$ depending on the value of $x,y$ <img src="./images/two_points_plane_wave.png" align="center" style="width: 500px";/> Note: * Correct Answer: A
The electric field of an E/M wave is described by: $$\mathbf{E} = E_0\sin\left(kx-\omega t\right)\hat{\mathbf{y}}$$ What is the direction of the magnetic field? 1. $+x$ 2. $+y$ 3. $–x$ 4. $+z$ 5. $-z$ Note: * Correct Answer: D