I am working through the following problem: The charging circuit for the flash s

Question

I am working through the following problem:

The charging circuit for the flash system of a camera uses a 130 muF capacitor that is charged from a 250V power supply.

What is the most resistance that can be in series with the capacitor if the capacitor is to charge to at least 86% of its final voltage in no more than 8.0 s?

I have the equation:

I = Io[1

Explanation / Answer

v= vo[1–e^(–t/rc)] =>0.86=1–e^(–t/rc) =>e^(–t/rc)=0.14 =>-8/(r*130*10^-6)=ln 0.14 =>8/(r*130*10^-6)=1.9661 =>8/(1.9661*130*10^-6)=r =>r=31300ohm now answered it correct

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