If you touch the two terminals of a power supply with your two fingertips on opp
ID: 1440488 • Letter: I
Question
If you touch the two terminals of a power supply with your two fingertips on opposite hands, the potential difference will produce a current through your torso. The maximum safe current is approximately 5 mA.
(a) If your hands are completely dry, the resistance of your body from fingertip to fingertip is approximately 515k. If you accidentally touch both terminals of your 125 V household electricity supply with dry fingers, what current will flow, and will you receive a dangerous shock?
(b) If your hands are moist, your resistance drops to approximately 1.8 k. If you accidentally touch both terminals of your 125 V household supply with moist fingers, what current will flow, and will you receive a dangerous shock?
Explanation / Answer
a) V = IR
where V = 125 Volt
R = 515 k ohm = 515 x 10^3 ohm
I = V/R = (125 ) / (515 x 10^3) = 0.243 x 10^-3 A = 0.243 mA
which is less than 5mA
hence no danger
b) now R = 1.8 x 10^3 ohm
I = (125) / (1.8 x10^3) = 69.44 x 10^-3 A = 69.44 mA
which is greater current than 5mA.
hence you will receive dangerous shock.