From key@physics.utoronto.ca Fri Apr 11 10:53:46 2008
Date: Fri, 11 Apr 2008 10:53:45 -0400
From: Tony Key <key@physics.utoronto.ca>
To: louisa.hong@utoronto.ca
Subject: Re: 

Hi Louisa - Look more carefully at the equation.  At t=0, exp(0) = 1, and
Mz=0.  At  t=infinity, exp(-infinity) = 0, so Mz = |M|.  From the graph, you
can read off what that value is.  (exp(-1) is NO equal to 1!.  T1 is a sort
of 'half-life, except that the function increases with time.  Find a time t
when Mz = |M|/2 - then you know that exp(-t/T1) = 1/2 - solve for T1.

Let me know if that works for you!

TonyK

louisa.hong@utoronto.ca wrote:
> Hi Prof. Key,
>
> How are you? My name is Louisa. I was doing mastering physics today and
> noticed something that took me half an hour trying to understand. You gave
> us the equation of T1, which is Mz = |M|[1-exp(-t/T1)]. I think |M| is the
> maximum M value, also I know that T1 is the time it takes for Mz to reach
> |M|. However, if I sub in T1 for t into the equation, Mz =/= |M|,because
> when t=T1, 1-exp(-t/T1)= 1- exp(-1) =/= 1! Is there something wrong with
> my logic? Please help me out. I hope you can understand my question. Thank
> you very much!
>
> Louisa Hong
>