A) How long must a mechanic wait before servicing a circuit with a fully charged
ID: 1696128 • Letter: A
Question
A) How long must a mechanic wait before servicing a circuit with a fully charged capacitor (C=470 microfarads), that has an initial charge of 250V, and is hooked up to a 1M ohm resistor. It is unsafe to touch the circuit if the capacitor has more than 1V.B) How much charge is contained by the capacitor when fully charged?
C) A 5-second prolonged electric shock of 235mA is fatal. Can the fully charged capacitor produce this much current for the entire 5 seconds?
D) A current of 75mA across the heart is sufficient to cause V-fib. If the resistance across the mechanics body is 30 kilo-ohms, will he be electrocuted if he touches the fully charged capacitor?
Explanation / Answer
A) R*C=1 E6 ohm*470 E-6 F=470 sec 1 V=250 V*e^(-t/(R*C))= Ln(1/250)*470=-t A) -2595.1 sec=-t therefore at least ---> t=2595 sec or 2595/60=43.25 minutes B) 250 V*470 E-6 F=117.5 mC or 117500 microC the energy: E=1/2*C*V^2=joules (energy) C) tau=time constant=470 sec/60=7.8 minutes for 1 time constant C) V/R*e^(-t/(R*C))=I: thus 250/1E*e^(-5/(470))=.247 mA ans no D) tau=470 microF*30000 ohms=14.1 s V/R*e^(-t/(R*C))=I:thus 250/30000*e^(-5/14.1)=5.85 mA at 5 seconds of current not electrocuted