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08 January 2014

Mail time: is the sign on electric potential energy important?

Joseph Rao, from my 2013 Manhattan College AP Summer Institute, writes in:

For AP Physics do we pay attention to the sign on Electric Potential energy?  I know we do not assign a sign to Electric field and do assign one to potential difference when calculating potential some distance from a source charge or charged plate. 

Hey, Joseph... the sign on electric potential energy is important, because objects are forced from high to low potential energy.  A charge released from rest with -30 J of PE will speed up to a place where it has -80 J of PE.  

Note this is different from electric potential (i.e. voltage).  A positive charge is forced high to low voltage, while a negative charge is forces low to high voltage.


1 comment:

  1. also, putting a sign on a vector (the electric field) isn't as meaningful as a sign on a scalar (the potential)