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  1. C

    Simple stats question

    Homework Statement The problem goes like this. I have two parameters A and B, both which can only be true or false ( booleans ). Then, the only information I have is that for x events for which A is true, B is also true y times. My question then is, what is the most I can get out of these two...
  2. C

    Hypothesis testing, confidance leves, photon statistics

    Homework Statement A source is supposed to emit photons with spin +/-1 independently at equal rate. a) after measuring 4 photons, all have spin +1; b) after measuring 100 photons, 60 have spin +1. at which confidence level can the hypothesis be rejected. Calculate for each of the...
  3. C

    Radiative transfer

    Homework Statement A galaxy consist of a uniform slab of stars mixed with dust. The slab has thickness L, and optical depth \tau for a ray passing perpendicularly through the slab. assume the emmisivity of the stars \epsilon and the density of dust is constand throught the slab. Further assume...
  4. C

    Nuclear Beta Decay (Parity, deta[L])

    Hey, I don't quite remember this but I'll try to explain how you do it for your first reaction. At the beginning, you can find the allowed values for L ( the orbital angular momentum ) via the angular momentum addition theorem: L = { |J1-J2|,..,|J1+J2|} in integer steps. As for the...
  5. C

    Absolute color - magnitude diagram

    Hey thanks for your answer. I have thought of that, but I wouldn't like to do that manually for ~100 stars.. Isnt any ready data table of absolute magnitudes and colors out there ( at least for near by stars? ) Thanks
  6. C

    Absolute color - magnitude diagram

    Hello all, I am finding a distance to a cluster via Main Sequence fitting, and I don't know where to find an absolute color - magnitude diagram ( B-V, and V ). I can be from any star cluster, or sky region, as long as the magnitudes are absolute. I need the data tables, not just a pretty...
  7. C

    Self Inductance

    Homework Statement Show that the self-inductance per unit length of a wire of radius R carrying a uniform current density inside, the current returning along the surface of the wire is μ0/8π. The Attempt at a Solution I thought that it might be simpler to calculate the self...
  8. C

    Conductors separated by interface

    Homework Statement The Plane z=0 forms an interface between two conductors of conductivity σ1 and σ2 respectively. In the 1st conductor a steady current J1 flows and it makes an angle θ1 with the normal of the interface. Find the current in the 2nd conductor and the charge density on the...
  9. C

    Force on a sphere in a constant external electric field

    It seemed too simple somehow... Is q the induced charge on the sphere, and E the electric field close to the sphere?? Thank you for your help
  10. C

    Force on a sphere in a constant external electric field

    Homework Statement An uncharged solid sphere is paced in a constant external electric field E0. What is the force on the sphere? Homework Equations The Attempt at a Solution I know ( already have found ) the electric potential and electric field around the sphere. Also worked out...
  11. C

    Electric Field of a Conducting Slab

    Is this supposed to be solved by the method of image charges, or that is something completely different? Well the charge induced at the surface of the slab will have the same magnitude as the point charge above it. But i am not sure what that tells me about the field since the geometry of the...
  12. C

    Inelastic Collision Problem. Help!

    Well.. you know that the collision is inelastic, so kinetic energy will not be conserved, but momentum will be. You know the masses and the velocities before the collision as well as their velocities, and you can safely assume that mass is conserved, you can use momentum conservation to find...
  13. C

    Elastic Collision in 2D between 2 Hard Spheres

    Homework Statement By resolving the momentum equations parallel and perpendicular to the incident beam direction, show that α is related to the speed v2 of the recoiling particle by: cos α = m2*v2/(2μ*u1) where μ=m1m2/(m1+m2) Homework Equations See attachment for diagram...
  14. C

    Experiment with Electric field lines

    Homework Statement Hello all. I need help or ideas on making an experiment in which I need to show the electric field lines. I think it should be somewhat similar the the experiment when you put lots of little metal pieces on a piece of paper and then you put a magnet below the paper, and...
  15. C

    QM step potential

    In my case, the energy of the electron is less then the step potential, so the marble example would apply. I could think of more examples if the potential was not infinite, but this complicate things.
  16. C

    QM step potential

    Thanks, that indeed makes sense.
  17. C

    QM step potential

    Homework Statement A step potential is defined by: V(x) = 0 ( for for x <0 ) and V(x) = V0 ( for x >0 ). Hence the step occurs at the origin. Suggest a real physical situation, that might correspond to this idealized problem Homework Equations None needed. The Attempt at a Solution...
  18. C

    Induction and EMF

    But from the original equation which is emf = - dΦ/dt, so this minus cancels out with the -3 minus.. I will redo it just in case. That's for all the help, you can count this one as solved ( I understood the main idea with the z being the only thing that changes with time! ). Thanks very much
  19. C

    Induction and EMF

    Is this anywhere near to correct?
  20. C

    Induction and EMF

    Sorry I made a typo.. should have been A* (μIR*R/2) * 3/( v^3 * t^4 ) but then still A* (μIR*R/2) * 3/( z^3*t )
  21. C

    Induction and EMF

    So will the emf be A* (μIR*R/2) * 3( v^3 * z^4 ) or I did it very very wrongly..
  22. C

    Induction and EMF

    Homework Statement In a ring of radius R, there is current I flowing in the counterclockwise direction as viewed from above. A small ring of radius r is on a common axis and is a hight z above the current carrying ring, where z>>R. The small ring moves up with velocity v. Calculate the emf in...
  23. C

    Addition of Potentials

    Homework Statement 27 drops of salt water with same radius, are each charged to a potential of V volts. They are made to coalesce into a single drop. How is the potential of a new drop compared to the potential of the original drops. Homework Equations V ( potential ) = k* q/r...
  24. C

    Single Plane?

    The motion of the mass and the rod is a circle. Circle lies in a place, perpendicular to the angular momentum vector of the objects moving round the hinge... I think
  25. C

    Work - Force - Energy

    I solved the integral and I got the same expression as in for the difference in kinetic energy, so it's gotta be right. Thanks for Your help!
  26. C

    Work - Force - Energy

    I know that the units are consistent. I have found the change in Kinetic energy, which is deltaK = 1/2 *v0^2 * [( R0^2 / R1^2 ) - 1 ]. But when I integrate mv1^2/R1 dR ( between R0 and R1 ), I get the very same expression but without the 1/2 factor at the start.. What am I doing wrong?
  27. C

    Work - Force - Energy

    Homework Statement A particle of mass m is tied to a string which goes through a hole in a smooth horizontal table. The particle moves in uniform circular motion with speed v0. The radius of the cricle is R0. By puling the string very slowly, the radius of the circular motion is reduced tao...
  28. C

    Simple Harmonic Motion of springs

    I checked, my working is correct, just multiply my equation by 2, you get the same answer. Algebra is all i have.. Thanks for everything!
  29. C

    Simple Harmonic Motion of springs

    maybe I start from the wrong thing.. I start from : ( 2k/m )^1/2 = 2Pi/T from there I got the thing written above