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Chapter 26, Problem 20P

(a)

To determine

The resistance of mercury.

(b)

To determine

The fractional change in the resistance during heartbeat.

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In one form of plethysmograph (a device for measuring volume), a rubber capillary tube with an inside diameter of 1.41 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 100.08 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 PHg = 9.4 x 10-7. m. (a) Calculate the resistance of the mercury. Ω (b) Calculate the fractional change in resistance during the heartbeat. Hint: Because the cylindrical volume is constant, V = A;L; = AƒLƒ and Aƒ = A;(L;/Lf). % increase
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, V = Ai Li = Af Lf and Af = Ai(Li/Lf).
Plethysmographs are devices used for measuring changes in the volume of internal organs or limbs. In one form of this device, a rubber capillary tube with an inside diameter of 1.00 mm is filled with mercury at 20.0°C. The resistance of the mercury is measured with the aid of electrodes sealed into the ends of the tube. If 100 cm of the tube is wound in a helix around a patient’s upper arm, the blood flow during a heartbeat causes the arm to expand, stretching the length of the tube by 0.040 0 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. Taking the resistivity of mercury to be 9.58 x 10-7 Ω ⋅ m, calculate (a) the resistance of the mercury and (b) the fractional change in resistance during the heartbeat. Hint: The fraction by which the cross-sectional area of the mercury column decreases is the fraction by which the length increases because the volume of mercury is constant.

Chapter 26 Solutions

Bundle: Physics For Scientists And Engineers With Modern Physics, Loose-leaf Version, 10th + Webassign Printed Access Card For Serway/jewett's Physics For Scientists And Engineers, 10th, Single-term

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