Department of Physics
RUSMART pages (weather)
Spring 2013 Classes & Info
My daily schedule
NSF REU Program (list of REU sites)
The Nucleus (resources for
pics from the north pole trip
the picture from the trip
Simple 2-liter water rocket
American Institute of Physics
Homework #8: Due Saturday, March 30 by 12 noon
- A wire has within it a current density given by J=J0r3z where the boldface z is the z unit vector, and J0=2,500Amp/m5. This will make the current bunch up towards the edges of the wire. The radius of the wire is 0.20cm. Find (a) the total current I in this wire, and (b) the magnetic field at a distance of 0.15m from the center of the wire.
- problem 6.30. Note that the magnetic field unit of 1 gauss=10-4Tesla. li>
- A proton from out sun hits Jupiter's magnetic field with a speed of 1.0x106m/s; assume the average value of this field throughout this problem is 35nT. Find (a) the Larmor radius of this proton's orbit in this field, (b) the Larmor frequency fL with which this proton goes around that circle, and (c) the electromagnetic power that this proton radiates while in this orbit.
- Ous SPS speaker on Friday, Dr. Rhon Keinigs, said something that I mentioned in class, and you've certainly heard it from the other physics profs: "Classically, atoms can't exist." Let's explore this.
a. Asumme that an electrons in a hydrogen atom is "held in its orbit" at r=0.53Angstroms by the electrostatic attraction between the electron and the proton. Find the speed of the electron is this circular orbit (ignore any relativistic effects).
b. Find the electromagnetic power radiated by this electron.
c. Assuming the electron only has its initial (non-relativistic) kinetic energy, find the time it would take for the electron to radiate away all of this energy if this classical situation was happening (and not the strange and wonderful world of quantum mechanics).
- An electron has been ejected from a supernova explosion and has a kinetic energy of 25MeV. Find (a) the speed of this electron, and (b) the potential difference that the supernova applied to the electron to get it to go this fast.
- A proton has been accelerated by a potential of 4.0 billion Volts by a neutron star and flung into space. Find (a) the speed of this proton, (b) the orbital radius of this proton when it encounters the interstellar magnetic field of 3x10-10T, and (c) the time it takes the proton to make one orbit in this field.
That's all for homework #8.