# Search results

1. ### A Ground Penetrating Radar formula

Are you saying that the energy is proportional to the SQRT of the dialectic constant, K?
2. ### A Ground Penetrating Radar formula

I am interested in the physics of ground penetrating radar. 1) Does anyone know where I can find a derivation of the formula in the attached jpg for the energy reflected? K=the dialectic constant. 2) An intuitive explanation of why the dialectic constant is important in determining the energy...
3. ### I Why is the speed of light absolute?

Does this FermiLab video help? "Why can't you go faster than light?" by Fermilab’s Dr. Don Lincoln
4. ### Work energy theorem

I read on the Internet that the work done by a (rigid) body = the change in Kinetic energy. What if I lift a rigid body slowly and vertically by 1 meter above the Earth's surface so that the initial velocity = final velocity =0? According to the Work Energy theorem as stated on many sites on...
5. ### EM Wave: Phase of the electric and magnetic waves?

In a vacuum, the plane wave solutions to Maxwell's Equations are... E=E0*cos(wt-kr) B=B0*cos(wt-kr) ie they are in phase. (See for example https://www.physics.wisc.edu/undergrads/courses/spring08/208/Lectures/lect20.pdf http://hyperphysics.phy-astr.gsu.edu/hbase/waves/emwv.html ) I don't...
6. ### That Heisenberg Uncertainity Principle

Does the Heisenberg Uncertainity Principle mean: 1) If a particle is confined within a length x then it must jiggle around with a momentum given by p ~ h/2x PI OR 2) If we measure the position of a particle to an accuracy of x then its momentum will be uncertain by ~ h/2x PI
7. ### Interaction of photons with charged particles

Does all this mean that a plasma is opaque to light of all wave lengths?
8. ### Interaction of photons with charged particles

Thanks. I'm trying to understand why light reacts with charged particles much more than with neutral atoms.
9. ### Interaction of photons with charged particles

Can someone please tell me the name of the theory describing the interaction of photons with charged particles eg electrons, protons? Can you also suggest a good introductory web page describing that theory at First Year University level for self study? Better still, a good VIDEO lecture on...
10. ### Aircraft lift - is it all Bernoulli's principle?

I find it hard to believe that the only factor important in computing aircraft lift is Bernoulli's principle. Doesn't good old Newton's Second Law play an effect? In other words simply deflecting the airflow downwards. Does anyone know the relative importance of these factors? (EG for a...
11. ### Reason the early Universe was opaque?

Apparently the early universe was opaque because the atoms were ionized. I'm wondering, why do electrons scatter photons but atoms don't? I'm presuming it's the electrons that do the scattering.
12. ### RELATIVITY: Co-ordinates of events

Thanks to you all. I think I'm starting to get the basics of SR!
13. ### RELATIVITY: Co-ordinates of events

I have reworked using a ruler length of L instead of 1m. I get: 1. The right end of the ruler passes the observer (in the observer's frame) (0,0) 2. The left end of the ruler passes the observer (in the observer's frame) (0,L/(u*gamma)) 3. The observer passes the right end of the ruler (in...
14. ### RELATIVITY: Co-ordinates of events

Thanks. I was expecting to get something like length/gamma ie length contraction!
15. ### RELATIVITY: Co-ordinates of events

Homework Statement A meter ruler moves at velocity u to the right past a stationary observer. The observer is at (0,0) in his rest frame. Give the (x,t) co-ordinates of the following events. 1. The right end of the ruler passes the observer (in the observer's frame) 2. The left end of the...
16. ### Special Relativity: Relative velocity

Homework Statement I know that if you have 2 observers, "A", one at rest and the other "B" moving wrt "A" and if the moving observer shoots a projectile, then we can calculate the velocity of the projectile wrt "A" using the standard equation shown below. I was thinking what equation would...
17. ### Magnetic monopoles are beyond me

1. So, if the universe is closed, there would seem to be no point in talking about monopoles. We could just talk about gigantic magnets? 2. And if the Universe is not closed, presumably one pole could move so far away from us that a light signal couldn't reach us from it (because of the...
18. ### Magnetic monopoles are beyond me

Still Puzzled! 1. Wouldn't this mean that there are as many north monopoles as there are south monopoles? In other words they come in pairs? 2. Suppose then there were just two monopoles in the (multi)universe, wouldn't this mean that the field would look identical to that of a (gigantic)...
19. ### Magnetic monopoles are beyond me

It was sometime ago so I don't recall the exact video. I did attempt to watch the early Cosmology Lectures by Leonard Susskind so it was probably mentioned in one of those. Sorry, I can't be more specific.
20. ### Magnetic monopoles are beyond me

How can you possibly have a magnetic monopole? The field lines must terminate somewhere, surely! I heard about them on a cosmology video on YouTube.
21. ### Find the velocity of the 14kg mass just before it hits the ground

Yes! Exactly! Here are my current thoughts. Taking down as positive: For 8Kg weight, where a is the acceleration of the 8Kg: 8a=-T1+8g For 14Kg weight where b is the acceleration of the 14Kg: 14b=14g-T2 For Pulley (since the tension on both sides of the string acts down)...
22. ### Find the velocity of the 14kg mass just before it hits the ground

Oops. Seems I skipped a step! Thanks. Intuitively 8a=T1-8g 14a=14g-T2 T1=T2 => (8+14)a= 14g-8g which gives the correct answer after a bit of algebra. ONE FURTHER QUESTION If the down direction is taken as positive, shouldn't these equations be... (T1 act upwards 8a=-T1+8g 14a=14g-T2 T1=-T2...
23. ### Find the velocity of the 14kg mass just before it hits the ground

Homework Statement A 14kg mass is attached to one side of a vertical pulley and an 8kg to the other. The 14kg mass is 5m above the ground. The 8kg is just resting on the ground. The pulley is frictionless and weightless. Find the velocity of the 14kg mass just before it hits the...