# Recent content by Dopplershift

1. ### Other Entering a PhD Physics Program While Teaching High School?

Hello, I am currently a high school physics teacher in Chicago. I am thinking about going back to school to get a PHD in Physics. I currently have a B.S. in Applied Physics and a secondary education license. I would like to find a way to go back and get a PHD. I cannot afford to quit my job...
2. ### I Understanding Continuous Variable QKD

So, I am doing my undergraduate research project in Quantum Cryptography, and I have some confusion in a few areas, especially in the topic of continuous variable quantum key distribution. From what I understand, Discrete Variable - Single photon. That is, for example, the BB84 protocol. Bob...

Thank you!
4. ### Rocket's Initial Mass

I'm confused, how is the initial velocity zero? It says that the fuel gives us a v0 of 3.0*105? The problem is when I plug in the values of the conditions into my final equation, (equation 2).
5. ### Rocket's Initial Mass

The problem states: Typical chemical fuels yield exhaust speeds of the order of 103 m/s. Let us imagine we had a fuel that gives v0 = 3 × 105 m/s. What initial mass of fuel would the rocket need in order to attain a final velocity of 0.1c for a final mass of 1 ton? I derived the equation in the...
6. ### Find Hamiltonian given Force

Homework Statement A particle with mass, m, is subject to an attractive force. $$\vec{F}(r,t) = \hat{e}_r \frac{k}{r^2}e^{-\beta t}$$ Find the Hamitonian of the particle Homework Equations H = T + U Where T is the kinetic energy and U is the potential...
7. ### Limits of Integration of a Triangle

That makes sense. Thank you! :)
8. ### Limits of Integration of a Triangle

You didn't misunderstood, I mistyped, my apologies. It is dZ. My limits I assumed are 0<y<1 0<x< y
9. ### Limits of Integration of a Triangle

How to I integrate if the integral is a sum such as dz = y dx + (x+2y)dy ? And are my limits of integration correct?
10. ### Limits of Integration of a Triangle

Homework Statement Suppose you have a Triangle with the vertices, (0,0) (1,1) and (0,1). Integrating along that path. I have some differential function dZ where Z = Z(x,y) Homework Equations The Attempt at a Solution [/B] If I need to integrate, then I need to find the limits of...
11. ### Need Help With Gradient (Spherical Coordinates)

Thank you, very much! :)
12. ### Need Help With Gradient (Spherical Coordinates)

So would it be: $$\begin{split} f(r) = rcos(\theta) \\ \frac{\partial f}{\partial r} = cos\theta \\ \frac{\partial f}{\partial \theta} = - rsin \theta \\ \frac{\partial f}{\partial \phi} = 0 \end{split}$$ So the gradient is cos\theta \ \hat{r} +...
13. ### Need Help With Gradient (Spherical Coordinates)

if you're asking if I know how to take partial derivatives, then yes. The issue lies in I don't know where to begin since there is ##\hat{r}##, ##\hat{\theta}##, ##\hat{\phi}## in the equation.
14. ### Need Help With Gradient (Spherical Coordinates)

Homework Statement Find te gradient of the following function f(r) = rcos(##\theta##) in spherical coordinates. Homework Equations \nabla f = \frac{\partial f}{\partial r} \hat{r} + (\frac{1}{r}) \frac{\partial f}{\partial \theta} \hat{\theta} + \frac{1}{rsin\theta}...
15. ### 3-D Dirac Delta Function

Never Mind, I figured it out. I was overthinking the problem. Thanks for your help! :)