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Tue 5 Jul, 2005 04:09 pm
The equation governing the amount of current I (in amperes) after time t (in seconds) in a simple RL circuit consisting of a resistance R (in ohms), an inductance L (in henrys) and an electromotive force E (in volts) is
I = E/R [1 - e^-(R/L)t]
If E = 12 volts, R = 10 ohms and L = 5 henrys, how long does it take to obtain a current of 0.5 ampere? of 1.0 ampere?
I plugged the given information into the formula above and used my calculator trying to solve for time or t but could not come up with the correct answer. What am I doing wrong? Can you show me the correct steps using a Tl -36x solar Texas Instrument calculator.
Rearrange the equation
If:
I = E/R [1 - e^-(R/L)t]
Then
IR/E = 1 - e^-(R/L)t
And
1- IR/E = e^-(R/L)t
And
ln (1 - IR/E) = -(R/L) t
And finally
-L/R * ln (1- IR/E) = t
Great
I can now plug the given information and find each answer thanks to you.
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