A neuromuscular microstimulator is a device designed to be implanted into paraly

Question

A neuromuscular microstimulator is a device designed to be implanted into paralyzed muscles or other tissue suffering neuromuscular dysfunction. The device supplies an electric current that stimulates the dysfunctional tissue. A particular device uses a capacitor built into a microchip: the capacitor can supply 10 mA of current for 200 mu s 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 The cell membrane separates the interior of a living cell from its surrounding. So-called ion channels penetrate the membrane, allowing passage of materials into and out of cell. (a) One channel opens for 1.0 ms and allows passage of 1.1 times 10^4 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 2.0 T 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 the deuterons? (c) If the p.d. is 1500 V, how many orbits do deuterons complete before achieving the maximum energy? 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 fail they revert to are resistance of 0.31 m Ohm. (c) Given that the current can't change instantaneously, find the power dissipation in the solenoid immediately after a sudden loss of superconductivity. (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 produce when electrons and positrons annihilate. (The positrons come from short-lived radioisotope introduced into the patient.) What is the energy of the gamma rays? Concept Mapping (a) Magnet (b) Static Electricity

Explanation / Answer

a) Using

Q = It = 10*10^-3*200*10^-6 = 2*10^-6 C = 2uC

b) Now

Using

Q = CV

C= Q/V = 2*10^-6/4.5 = 0.44 uF

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