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I'm a bit of a noob when it comes to EE, so this might be a dumb question, but I find it super interesting and am learning as fast as I can

(1) I saw the following formula on another forum: "E = 0.5 * C * V^2 = 4 mJ"

Describing the energy that a gag shock pen would inflict on a human. I am confused how the op got to this conclusion. I read on a different site that energy = power * time where power equals V(voltage) * I(current), so I'm not sure where the 0.5, the C, and the second V comes in.

Does C stand for current? or is it some kind of constant? any explanation would be appreciated, Thanks!

(2) Also related follow up question, the thing I was initially trying to find out for curiosity and to kind of understand what a safe current is, is how much current a shock pen would have, assuming a voltage of about 50- 70 V

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    \$\begingroup\$ Capacitance in this context. (In other contexts, the speed of light, but not here.) \$\endgroup\$
    – user16324
    Commented Feb 3, 2021 at 15:27

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C in the equation

\$E = \frac{CV^2}{2}\$

refers to capacitance.

A capacitor with capacitance C which is charged to voltage V has

\$E = \frac{CV^2}{2}\$ energy stored in it.

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  • \$\begingroup\$ Thank you! that's the missing piece I needed \$\endgroup\$
    – Dyskord
    Commented Feb 3, 2021 at 2:10
  • \$\begingroup\$ would C be in farads in this equation? assuming E is in joules? \$\endgroup\$
    – Dyskord
    Commented Feb 3, 2021 at 2:13
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    \$\begingroup\$ @Dyskord yes. That would be correct. \$\endgroup\$
    – Math Keeps Me Busy
    Commented Feb 3, 2021 at 2:14

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