[sdiy] Newbie Electronics Math problem (I need help!)

[Tim Stinchcombe]

> You're missing nothing here.  You are correct.  Either the 
> textbook is wrong, or it's a "trick question" (which is what 
> I always tell my students when I've f***ed up a problem!).
> 
> P = VI = E/t
> 
> Ergo, V = E/I/t = E/Q
> 
> I.e., no t, no V.  V could be anything, since it is just the 
> driving force. If it takes 17 years for that 0.0025 J to be 
> expended, then obviously the driving force needn't be very 
> high!  If it takes a nanosecond, then it is pretty high!

Maybe it's a test of how well you understand the units/dimensions involved?
I.E. leave the time in the expression as an 'unknown', so that it is
25millisomethings per second? The question then arises as to whether to say
this is 25mJ per amp per second, or even 25mV-seconds per second? Is that a
bit harsh, or do I have it completely wrong? (Quite likely - either way it
is a bit of a mind-f*ck...never could get on with such dimensional-type
questions because of that).

Tim
__________________________________________________________
Tim Stinchcombe 

Cheltenham, Glos, UK
email: tim102 at tstinchcombe.freeserve.co.uk
www.timstinchcombe.co.uk