Show that the energy of a charged conducting sphere in vacuum is kq²/(2R)

[jennyyyy]

Homework Statement

Show that the energy associated with a conducting sphere of radius R and charge q surronded by a vacuum is given by u=kq^2/(2R).

Homework Equations

The Attempt at a Solution

 

[Hootenanny]

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[jennyyyy]

i couldn't do anything. what is u ?where does it come from i don't understand :( pls help me and sorry for my english i don't know perfect english

 

[CompuChip]

Welcome to PF jennyyyy. U is just the name used to denote the energy you are asked to calculate:

Show that the energy u associated with a conducting sphere ... is given by $k q^2 / (2 R)$

Are you using a book for your electrodynamics course, or lecture notes? Surely there must be something about energy in there, like a formula you could use.