Work in a uniform electric field

[malek2771999]

I need a little help here
when calculating the work done in a uniform electric field on a positive charge to move it from point a at higher potential to point b at lower potential that means the charge is going towards the negative plate we first use V = - ED and then we have a negative V then we use W = qv and we have a negative work that means the work is done by the system not external force and that's what happened because a positive charge in a electric field will always go towards the negative plate is everything I did here correct? Because in my textbook the formula for work is W= - qv and it's confusing me please help my exam is tomorrow :)

 

[Dale]

The first step is to think about the situation physically and figure out which way energy is going. Since you have a positive charge going from a high potential to a low potential this is energy going from the field to the charge. So if W is positive the W is the work done by the field on the charge, and if W is negative then it is the work done by the charge on the field.

Importantly, not everything labeled W means the same thing.