Why is it Va - Vb, why not Vb - Va?
Solution,
Work is done by an electric field on a charge particle when a positive charge moves in the direction of the electric field or when a positive charge moves from high potential to low potential. So, since WE denotes the work done by the electric field on the charge when it is moving from A to B, it have been defined as qo(VA - VB). No, this will be negative when VA < VB and positive when VA > VB. Accordingly, the external work done will be positive (is to be done on the system) or negative (done by the system).
Work is done by an electric field on a charge particle when a positive charge moves in the direction of the electric field or when a positive charge moves from high potential to low potential. So, since WE denotes the work done by the electric field on the charge when it is moving from A to B, it have been defined as qo(VA - VB). No, this will be negative when VA < VB and positive when VA > VB. Accordingly, the external work done will be positive (is to be done on the system) or negative (done by the system).