An approximation for exponential.

AI Thread Summary
An approximation for exp(-k*L) when L is large but finite is under discussion, with the limit as L approaches infinity suggesting a useful approximation. The conversation highlights that while calculus provides insights, the approximation must consider the entire power series rather than truncating it to the first few terms. It is noted that negative exponents complicate the use of simple approximations, as the full series expansion is necessary for accuracy. The discussion emphasizes that k is assumed to be positive, which influences the behavior of the function. Overall, a comprehensive approach using power series is recommended for better accuracy in approximating the exponential function.
Alta
Messages
13
Reaction score
0
Is there an approximation for exp(-k*L) with L large but finite??
 
Physics news on Phys.org
Well, what is
\lim_{L \to +\infty} e^{-kL}​
? Doesn't calculus tell you that limit would be a good approximation?

(P.S. are you making any assumptions about k? )
 
L is large but finite. No assumptions about k but it is positive.
 
Power series. Use as many terms as you like to improve accuracy.
I can't seem to do Latex code, but you'll find it here about a screenfull down.
http://en.wikipedia.org/wiki/Power_series

Oops - no good for negative exponent!
 
The trouble with that is that you can not say that exp(-k*L)=1+-k*L. you need the entire sum.
 
Thread 'Variable mass system : water sprayed into a moving container'
Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
I was thinking using 2 purple mattress samples, and taping them together, I do want other ideas though, the main guidelines are; Must have a volume LESS than 1600 cubic centimeters, and CAN'T exceed 25 cm in ANY direction. Must be LESS than 1 kg. NO parachutes. NO glue or Tape can touch the egg. MUST be able to take egg out in less than 1 minute. Grade A large eggs will be used.
Back
Top