The human body is a complex and beautiful marvel of Evolution. It is also a bag of salty water with resistivity 5Ω⋅m . Let's get a sense for the inherent danger of different voltages applied across the body. From left hand to right hand, we approximate the body / torso as a tube 1.6 m long, 10 cm in diameter. We will consider two skin conditions -- wet skin (e.g. with salt water on it) in which case the skin's resistance is negligible, and dry skin which has much higher resistance. 1. First, if the skin is wet, what is the resistance from left hand to right hand (in ohms, to 3 significant digits)? 2. If the resistance from right hand to left is 500kΩ when skin is dry, what is the resistance of a single layer of dry skin (answer in kΩ , with 2 significant digits)? 3. A current of 100 mA passing from right hand to left can easily be lethal. If your hands are dry, what voltage is lethal (2 significant digits)? 4. A current of 100 mA passing from right hand to left can easily be lethal. If your hands are wet, what voltage is lethal (2 significant digits)? Note household wall voltage is ~120 V.
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The human body is a complex and beautiful marvel of Evolution. It is also a bag of salty water with resistivity 5Ω⋅m . Let's get a sense for the inherent danger of different voltages applied across the body. From left hand to right hand, we approximate the body / torso as a tube 1.6 m long, 10 cm in diameter. We will consider two skin conditions -- wet skin (e.g. with salt water on it) in which case the skin's resistance is negligible, and dry skin which has much higher resistance.
1. First, if the skin is wet, what is the resistance from left hand to right hand (in ohms, to 3 significant digits)?
2. If the resistance from right hand to left is 500kΩ when skin is dry, what is the resistance of a single layer of dry skin (answer in kΩ , with 2 significant digits)?
3. A current of 100 mA passing from right hand to left can easily be lethal. If your hands are dry, what voltage is lethal (2 significant digits)?
4. A current of 100 mA passing from right hand to left can easily be lethal. If your hands are wet, what voltage is lethal (2 significant digits)?
Note household wall voltage is ~120 V.
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