Question

Va-Vb=integral Edl from a to b
why isn't it from b to a?

Answer 1

it is so because , the potential decreases in the direction of the electric field.
and when we are calculating the P.D between two points A & B ,we should consider the direction of the electric field between those two points so ,Va-Vb will be integral from a to b ,if we do the converse i,e integral from b to a we are calculating the potential in the reverse direction so we get the same magnitude of P.D ,but with opposite sign.

Answer 2

actually,
∫abqUdl=∫abFdl=ΔK=−qΔU
So,
∫abUdl=−ΔU=−Edl
Then,
Ua−Ub=EΔl

Answer 3

IT WOULD BE MUCH BETTER IF YOU CONNECT IT WITH A SITUATION(CIRCUIT) .

Answer 4

Thanks guys! :)