no tagsHomework003SteveSekula, 8 February 2011 (created 5 September 2010)Homework 3Expectations for the quality of your handed-in homework are available athttp://www.physics.smu.edu/sekula/phy1308/homework.pdf. Failure tomeet these guidelines will result in loss of points as detailed in thatdocument.Reading Assignment:Chapter 22, Chapter 23Practice Problems:These are not required; they are odd-numbered problems from Wolfsonthat may help you to warm up for the required problems.CH22-21CH22-49CH23-22 (Answer: )Required Problems:SS-8 [20 Points]SS-9 [20 Points]General Physics - E&M (PHY 1308) LectureNotesGeneral Physics - E&M (PHY 1308) LectureNotesC :2 0 F = 2  1À8General Physics - E&M (PHY 1308) - Lecture Notes file:///home/sekula/Dropbox/Documents/Notebook...1 of 5 02/08/2011 05:38 PMCH23-30 [10 Points]CH23-32 [10 Points]Problem SS-8Medical facilities, such as hospitals, often contain a device known as a"particle accelerator" for use in cancer therapies. Particle accelerators useelectric fields to accelerate electrically charged particles to high speeds.They were originally developed for use in the study of subatomic particles,but have found many uses in industry and medicine.Medical linear accelerators are used to make a beam of particles that canpenetrate the body. The particles then deposit the energy gained duringacceleration into tumor material. Greenwich Hospital in New York boastson its website that it has " . . . one of the newest generations of linearaccelerators used in radiation therapy." (http://www.greenhosp.org/medicalservices_cancer-treatment-radiation-treatment.asp).Electrons are the typical particle of choice in such cancer therapy, as theyare cheap to obtain in large quantities and easy to accelerate. If, duringmedical therapy, a beam of electrons strikes the skin with an energy of (million electron-Volts):Through what potential was it accelerated to reach this energy?1.If a medical linear accelerator brings electrons from rest (zero energy)up to in 4.0 meters, what is the magnitude of the electric fieldused in acceleration?2.(More about medical accelerators: http://www.radiologyinfo.org/en/info.cfm?pg=linac)Problem SS-9The neuron is a complex cellular structure whose job is to transmitinformation, in the form of electrical impulses, throughout the nervoussystem of a living organism, such as a human. Neurons consist ofdendrites, which connect one neuron to another; the soma (central cell10:0MeV 10:0MeV General Physics - E&M (PHY 1308) - Lecture Notes file:///home/sekula/Dropbox/Documents/Notebook...2 of 5 02/08/2011 05:38 PMbody of the neuron which processes information from the dendrites); theaxon (the long "cable" behind the soma that transmits impulses to the axonterminal); and the axon terminal, which connects via synapses to otherdendrites on other neurons. See image below. The complex interaction ofneurons plays a central role in decision making, learning, memory, and islikely the cellular foundation of consciousness.The axon is essentially an example of a "coaxial cable" - this is a cablemade from a small wire running along the central axis of a largercylindrical conductor (the "sheath"). In the axon, the sheath is a chemicalcalled "myelin," which is produced by glial cells.Let us treat the axon as a very long coaxial cable (this is not unreasonable -some axons, as in the spine, can be up to a few feet long). This is illustratedbelow. The myelin sheath can be treated as a thin-walled cylindricalenclosure with a diameter of . The axon filaments in the center can betreated as a wire with a diameter of ; this filament wire runsalong the central axis of the myelin cylinder and carries a uniform linearcharge density. Treat the filament and the myelin as conductors.What is the formula for the electric field inside the cylinder due to thefilament? HINT: what is the electric field outside of a cylinder carryinga linear charge density, ?1.1:0Öm 1:0 0 m  1À8Õ General Physics - E&M (PHY 1308) - Lecture Notes file:///home/sekula/Dropbox/Documents/Notebook...3 of 5 02/08/2011 05:38 PMWhat is the electric potential difference between the outer surface ofthe filament, located at , and the inner surface of the sheath, locatedat ?2.The resting electric potential difference in a typical neuron is -70.0mV. What is the linear charge density on outer surface of the centralfilament?3.What is the capacitance of this axon if its length is ?4.r Ar B1:0m General Physics - E&M (PHY 1308) - Lecture Notes file:///home/sekula/Dropbox/Documents/Notebook...4 of 5 02/08/2011 05:38 PMGeneral Physics - E&M (PHY 1308) - Lecture Notes file:///home/sekula/Dropbox/Documents/Notebook...5 of 5 02/08/2011 05:38
View Full Document
Unlocking...