# Recent content by unified

1. ### PN Junction at Equilibrium

phyzguy, A sketch would include four currents, two from the field (electrons move against the field, holes with the field) and two due to random thermal motions (electrons from P to N, holes from N to P). In equilibrium these effects cancel.
2. ### PN Junction at Equilibrium

Consider a PN junction doped with say phosphorous on the N side, and Boron on the P side. Initially, there is an opportunity for the electrons just below the N conduction band to drop to the lower available energy states just above the P valence band. This leaves the N side positively charged...
3. ### I Phase Speed of Wave in non-relativistic Doppler Shift Derivation

To answer my own question, we are comparing the frequency measured by the ground observer -- who is at rest relative to the medium air -- with that measured by an observer moving with the siren and at rest relative to the air. Since they are both at rest relative to the air, they will measure...
4. ### I Phase Speed of Wave in non-relativistic Doppler Shift Derivation

Consider the situation where an observer at rest on the ground measures the frequency of a siren which is moving away from the observer at speed ##v_{Ex}##. Let ##v_w## be the speed of the sound wave. Let ##\lambda_0##, ##f_0##, ##\lambda_D##, and ##f_D## be the wavelengths and frequencies...
5. ### Generalized Lorentz Transformation

If what I have is a valid transformation, then I'm confused about what is calculating. Given the coordinates in S, does it give the coordinates in S(bar)?
6. ### Generalized Lorentz Transformation

I noticed that of course. But, isn't it true that the matrix gives S(bar) in terms of S? I don't see how the logic could be wrong. We give S(bar) in terms of S' and S' in terms of S, thus S(bar) in terms of S. I agree the formula is not a boost, but isn't it still correct?

12. ### A simple Proper Time Calculation

Integral updated to include a dt term.
13. ### A simple Proper Time Calculation

Thanks for taking a look at it. The dimensions are correct. I'm using relativistic units, so |a| has units of 1/s. I'll email the professor and see if he is in agreement with our answers.
14. ### A simple Proper Time Calculation

Homework Statement Suppose a spaceship starts from rest from a space station floating in deep space and accelerates at a rate of |a| relative to the space station for 1.0 Ms. It then decelerates for the same amount of time at the same constant rate |a| to arrive at rest at another space station...
15. ### Tension on a string attached to two objects

OK, I see your point. The friction argument shouldn't matter anyways, because the result still holds in a friction free environment. Of course what I meant was the net forces acting on the person, so friction from the ground plus the two Tensions all sum to 0. But, I like the way you are...