Spring 2017 PHYS 204 Answer all questions. For credit show the work where necess

Question

Spring 2017 PHYS 204 Answer all questions. For credit show the work where necessary double-helix a DNA molecule acts like a spring that can be compressed Biophysicists estimated the force constant for one type of DNA mo to be 60 compression um-long DNA molecule that requires a charge of pc and at one 2 A d and -1.2 pC at the othe muscles or ular ulator is a device designed to be implanted into paralyzed other tissue suffering neuromuscular dysfunction. The device supplies an electric current th stimulates the dysfunctional tissue. A particular device uses a capacitor built into a microchip: the capacitor can supply 10 mA of current for 200 us before it's fully discharged (a) Find the initial charge on the capacitor and (b) the capacitance if it's initially charged to 4.5 V 3. The cell membrane separates the interior of a living cell from its surrounding. So-called ion channel penetrate the membrane, allowing passage of materials into and out of cell (a) one channel opens for 1.0 ms and allows passage of x 10' singly ionized K during this time. What is the current in the current in the channel? (b) What is the resistance of the ion channel if the potential difference across the channel in (a) is 80 mV. (c) This ion channel can be modelled as a cylinder with a length of 6.0 nm and a diameter of 0.35 nm. What is the resistivity of the fluid filling the channel? (d) At what rate is the energy dissipated while the ions are flowing? A medical cyclotron with a 2 magnetic field is intended to accelerate deuterium nuclei (deuterons), consisting of one proton and one neutron (a) At what frequency should the potential difference (p.d.) between the dees be alternated? (b) If the vacuum chamber has a diameter of 0.90 m, what is the maximum kinetic energy of the deuteron (c) If the p.d. is 1500 v, how many orbits do deuter complete before achieving the maximum energy 5. An MRI scanner uses a large solenoid with inductance of 0.53 H. carrying 2.4 kA of current (a) What's the energy stored in the solenoid? (b) The solenoid coils are normally superconducting (zero resistance), but if superconductivity fails they revert to are resistance of 0.31 mm. (c) Given that the current can't change instantaneously, find the power dissipation in the solenoid immediately after a sudden loss of superconductivity 6. (a) A positron is the antiparticle of the electron, with the same mass but charge +e. Find the minimum energy required to produce an electron-positron pair (b) Positron-emission tomography (PET images body tissues by detecting gamma brays produced 7. hen electrons and positrons annihilate. (The positrons come from short-lived radioisotopes introduced into the patient.) What is the energy of the gamma rays? Concept Mapping (a) Magnet (b) Static Electricit

Explanation / Answer

force constant, K=0.6 nN/nm

K=0.6 N

r=75*10^-6 m

q1=1.2*10^-12 C and q2=-1.2*10^-12 C

====>

F=k*x

(1/4pi*eo)*q1*q2/r^2 = K*x

9*10^9*(1.2*10^-12*1.2*10^-12)/(75*10^-6)^2= 0.68*x

====> x=3.38*10^-6 m

compression, x=3.38 um

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