# Electric potential difference between coaxial cables clarification

In this video, he derives an expression for the potential difference between the two radii R2 and R1 where R2>R1

He arrives at the derivation by integrating the electric field with respect to radius. But his integration limits are from R1 to R2 (2:18 in video)

Whats the reason behind this?

I'm not understanding the basis of putting a lower value at the top of the integration and a higher value at the bottom, as I've always done the opposite.

• You're aware that flipping the limits of integration simply multiplies the integral by $-1$, correct? – probably_someone Jul 23 '19 at 13:32
• @probably_someone yes but is that all there is to it? In the video it seemed like there was a more of a reason behind it? But I guess the only reason he did it was so that the equation was positive at the end. – elliris Jul 23 '19 at 14:12