Problem 22.67 It\'s possible to estimate the percentage of fat in the body by me

Question

Problem 22.67

It's possible to estimate the percentage of fat in the body by measuring the resistance of the upper leg rather than the upper arm; the calculation is similar. A person's leg meas-ures 40 cm between the knee and the hip, with an average leg diameter (ignoring bone and other poorly conducting tissue) of 12 cm . A potential difference of 0.74 V causes a current of 1.6 mA .

Part A

What are the fractions of muscle and fat in the leg?

Express your answer using two significant figures separated by a comma.

Explanation / Answer

from ohms law

V = I*R

R = V/I

R = resistance = rho*L/A

rho = resistivity

L = length = 0.4 m

A = area of cross section = pi*r^2 = pi*0.06^2 = 0.0113 m^2

rho = RA/L = VA/IL

rho = (0.74*0.0113)/(1.6*10^-3*0.4) = 13.1

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