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In two books I have used for physics course, the work done is taken to be positive when direction of displacement of charge and electric field is same and this positive works means that work is done by the field. Is that text using the definition the other around? Is that text taking work done to be negative when it's done by the field?
However, when you "find the work done to move the charge", it is of opposite sign from the work done by the charge/field.
Hence, this implies that if an external source supplies energy and the charge gains energy, the work is positive. This is why they start the calculation off with a negative sign in the equation for work W.