Current Electricity - current flowing through hand

[sharkey1314]

Current Electricity -- current flowing through hand

Homework Statement

i)For a layer dry skin 1mm thick, determine the resistance of a 1 cm^2 area of skin.
Resistivity of dry skin : 3 x 10^4 ohms m

[3.0 x 10^5 ohms ]
ii)A person, who is well-earthed, accidentally grabs a wire of diameter 0.4 cm at a potential of 50V. His hand makes contact with the whole circumference of the wire over a distance of 9cm.
The average thickness of skin of his hand is 1mm. Estimate the current flowing through him.

[1.89 mA ]

Homework Equations

Resistance = resistivity(length)/area
V = IR

The Attempt at a Solution

For i) , I managed to solve it.
Using the equation directly.

For ii), I couldn't get the answer.

First, I calculate the surface area of the cylinder ( wire ) where it is in contact with the wire.

Surface area = pi . diameter . length
= pi . (0.4 x 10^-2) . (9 x 10^-2)
= 0.0011309 m^2
Then I multiply this surface area with the resistance of dry hand obtain in i)

Total resistance = surface area x resistance of dry skin 1 mm thick, area of 1m^2
= 0.0011309 x 3.0 x 10^5

Next, I used V = IR. Sub in total resistance and P.D of 50 V
The answer I got was 0.147 A. Totally off.

Thanks for the time !

 

[tiny-tim]

hi sharkey1314!

Then I multiply this surface area with the resistance of dry hand obtain in i)

but won't the resistance go down if the area of contact increases?

 

[sharkey1314]

Thanks a lot. I re-used the equation for resistance to find the new resistance of the hand. Then, after using V = IR, I managed to get the answer =D

Just to clarify, what does a potential of 50V means ? And does the potential changes along the length of the wire. i.e. the start and end point will have different potential ? If so, does the answer change since potential varies.

 

[tiny-tim]

Just to clarify, what does a potential of 50V means ?

it means the potential difference between the wire and the ground …

ie from your hand to your foot! ​

And does the potential changes along the length of the wire. i.e. the start and end point will have different potential ? If so, does the answer change since potential varies.

Yes, but only very slightly …

the drop in potential along a wire is IR, and R for a wire is usually very small!

 

[rwisz]

I would like to clarify that the calculation for the current flowing through a person in this scenario is not as straightforward as using the equation V = IR. This is because the human body is not a simple resistor, but rather a complex system of tissues and fluids with varying resistances. Additionally, the skin is not always a constant thickness and can vary greatly depending on factors such as hydration and age.

To accurately calculate the current flowing through a person in this scenario, we would need to consider the specific resistance of each tissue and fluid in the body, the distribution of potential along the wire, and the effects of skin thickness and contact area. This would require specialized equipment and knowledge in the field of bioelectricity.

Furthermore, it is important to note that contact with a potential of 50V can be dangerous for humans, as it can cause electric shock and other harmful effects. I would advise against intentionally exposing oneself to electrical currents without proper safety measures and precautions in place.