For how long will the current across his chest exceed the danger level of 50 mA?
ID: 778570 • Letter: F
Question
For how long will the current across his chest exceed the danger level of 50 mA? For how long will the current across his chest exceed the danger level of 50 mA? Large capacitors can hold a potentially dangerous charge long after a circuit has been tuned off, so it is important to make sure they are discharged before you touch them. Suppose a 120 AF capacitor from a camera flash unit retains a voltage of 140 V when an unwary student removes it from the camera Part A If the student accidentally touches the two terminals with his hands, and if the resistance of his body between his hands is 1 8 k for how long wil the current across his chest exceed the danger level of 50 mA? Express your answer with the appropriate units. O ? Submit X Incorrect: Try Again; 8 attempts remainingExplanation / Answer
Given data
R=1800 ohm, C=120*10^-6 F, Vo=140 v, I=50*10^-3 A
Calculate the time
current, I=Io*e^-(t/RC)
50*10^-3=Vo/R*e^-(t/(1800*120*10^-6)
50*10^-3=(140/1800)*e^-(t/(1800*120*10^-6)
===> t=0.074 sec
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