Dielectric-Dielectric Boundary Conditions

[jegues]

Homework Statement

No problem, I just have a confusion about a certain concept.

Homework Equations

The Attempt at a Solution

I'm confused as to how they draw the result,

\oint_{C} \vec{E} \cdot \vec{dl} = E_{1t}\Delta l - E_{2t}\Delta l = 0

You don't really need to do the integration since,

\Delta l

is so small. Thus the result must be,

E_{net} \Delta l

But why is it such that,

E_{net} = E_{1t} - E_{2t}?

It looks as though they are pointing in the same direction in the figure.

Can someone explain? Am I mixing some things up?

Thanks again!

 

[SammyS]

\vec{\Delta l\phantom{ll}} is to the right in one medium, to the left in the other.

 

[jegues]

\vec{\Delta l\phantom{ll}} is to the right in one medium, to the left in the other.

Doh.

Thank you.