The maximum safe current through a normal person is 5.0 mA. A repair technician

Question

The maximum safe current through a normal person is 5.0 mA. A repair technician touches the hot wire in an appliance opened (or servicing and thereby comes into contact with 120 V. Will he receive a harmful shock: (i) if his hands are wet and the resistance of the path through him to the ground is 8,000 ohms? Show your work. (ii) If his skin is dry and he is wearing rubber soled shoes giving a resistance of 500,000 ohms to ground. Show your work. (iii) A current of 20 times 10^-6 Amps applied directly to the heart (perhaps by accident during surgery) may cause ventricular fibrillation If the resistance of a human heart is 300 ohms, what is the smallest voltage that poses a danger when the heart is exposed during surgery?

Explanation / Answer

calculate the current in each case:

(a)   current = voltage / resistance = 120 /8000 = 0.015 amps = 15 mA - Danger

(b)             current = 120 / 500000 = 0.00024 amps = 0.24mA - No danger

c) V = IR = 20x10^6 *300 = 6x10^3V = 6.0mV

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