ance of the mercury is measured with the aid of electrodes sealed into the ends of the tube. If 100.00 cm of the tube is wound in a spiral around a patient's upper arm, the blood flow during a heartbeat causes the arm to expand, stretching the tube to a length of 100.20 cm. From this observation, and assuming cylindrical symmetry, you can find the change in volume of the arm, which gives an indication of blood flow. Take ?Hg = 9.4 ✕ 10−7 Ω · m. (a) Calculate the resistance of the mercury. (b) Calculate the fractional change in resistance during the heartbeat. Hint: Because the cylindrical volume is constant, V = Ai Li = Af Lf and Af = Ai(Li/Lf).
In one form of plethysmograph (a device for measuring volume), a rubber capillary tube with an inside diameter of 1.30 mm is filled with mercury at 20°C. The resistance of the mercury is measured with the aid of electrodes sealed into the ends of the tube. If 100.00 cm of the tube is wound in a spiral around a patient's upper arm, the blood flow during a heartbeat causes the arm to expand, stretching the tube to a length of 100.20 cm. From this observation, and assuming cylindrical symmetry, you can find the change in volume of the arm, which gives an indication of blood flow. Take ?Hg = 9.4 ✕ 10−7 Ω · m.
(a) Calculate the resistance of the mercury.
(b) Calculate the fractional change in resistance during the heartbeat. Hint: Because the cylindrical volume is constant,
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