Large capacitors can hold a potentially dangerous charge long after a circuit has been turned off, so it is important to make sure they are

Question

Large capacitors can hold a potentially dangerous charge long after a circuit has been turned off, so it is important to make sure they are discharged before you touch them. Suppose a 120 μF capacitor from a camera flash unit retains a voltage of 140 V when an unwary student removes it from the camera. If the student accidentally touches the two terminals with his hands, and if the resistance of his body between his hands is 1.8 kΩ, for how long will the current across his chest exceed the danger level of 50 mA?

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Trung Dũng 4 years 2021-08-11T11:54:18+00:00 1 Answers 94 views 0

Answers ( )

  1. quangkhai
    0
    2021-08-11T11:55:45+00:00
    Reply

    Answer:

    93.3×10^-3s

    Explanation:

    If

    Resistance = 1.8 kΩ

    Current = 50 mA

    Capacitor = 120 μF

    Voltage = 140 V

    to calculate the discharge current

    Applying the formula of discharge current

    io=vo/R

    io= 140/ 1.8x 10³

    = 0.078A

    to calculate the time

    Applying the formula of current

    io= vo/R e-t/RC

    50= 140/1800e-t/RC

    0.649= e-t/RC

    -t/RC= ln( 0.649)

    t = 0.432x 120×10^-6x 1800

    t=93.3 x 10^-3seconds

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