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Get Full Access to College Physics - 1 Edition - Chapter 20 - Problem 18cq
Get Full Access to College Physics - 1 Edition - Chapter 20 - Problem 18cq

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# Using an ohmmeter, a student measures the resistance

ISBN: 9781938168000 42

## Solution for problem 18CQ Chapter 20

College Physics | 1st Edition

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Problem 18CQ

Problem 18CQ

Using an ohmmeter, a student measures the resistance between various points on his body. He finds that the resistance between two points on the same finger is about the same as the resistance between two points on opposite hands—both are several hundred thousand ohms. Furthermore, the resistance decreases when more skin is brought into contact with the probes of the ohmmeter. Finally, there is a dramatic drop in resistance (to a few thousand ohms) when the skin is wet. Explain these observations and their implications regarding skin and internal resistance of the human body.

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Solution 18CQ

Ohmmeter is a device used to measures resistance between the two points.

The resistance between two points on the same finger is same as the resistance between two points on the opposite hand is due to the geometric symmetricity of the body and the path provided to the current to flow through the body.

Also as the area of contact increases, when more skin is brought into contact with the probes of the ohmmeter, so the resistance decreases as,

R =

Here,  is the area provided for the flow of current.

Again, when the skin was wet, the drastic drop in resistance was due to the ions present in the liquid that makes path conducting and hence increases the conductivity of the skin greatly.

Step 2 of 3

Step 3 of 3

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