The average resistivity of the human body (apart from surface resistance of the

Question

The average resistivity of the human body (apart from surface resistance of the skin) is about 4.5 ·m. The conducting path between the hands can be approximated as a cylinder 1.5 m long and 0.10 m in diameter. The skin resistance can be made negligible by soaking the hands in salt water.

(a) What is the resistance between the hands if the skin resistance is negligible?


(b) If skin resistance is negligible, what potential difference between the hands is needed for a lethal shock current of 95 mA? Your result shows that even small potential differences can produce dangerous currents when skin is damp.
V

(c) What power is dissipated in the body by the current in b?
W

Explanation / Answer

a) length of hands = 1.5 m , cross section area = pi r^ 2 = pi x (0.05)^2 = 7.85x 10^3-

so Resistance = resistivity x length / area

= 4.5 x 1.5 / (7.85 x 10^-3) = 859.44 ohm

b) V = IR = 95 x 10^-3 x 859.44 =81.65 V

c) P = VI = 81.65 x 95 x 10^-3 = 7.76 W

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