MTW Ch7: Choosing Lagrangian for Scalar Potential

[TerryW]

I have managed to get to the end of Chapter 6 and have done almost all of the exercises (I didn't get anywhere with exercise 5.6 (d) and have seen the Cesarth/TSny exchange and still don't feel I have a satisfactory solution...) but I have hit a bit of a wall with Exercise 7.1 (a).First question is 'Why choose e^φ instead of just φ in the integral for I ?'Next question 'Can anyone give me a hint as to how I should be approaching this?'
I've attached my manuscript working which achieves a result of 0 = 0 (well at least it is consistent) but no differential equations.
Regards
TerryW

 

[Greg Bernhardt]

Thanks for the post! Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?