# Dielectric-Dielectric Boundary Conditions

1. Oct 9, 2011

### jegues

1. The problem statement, all variables and given/known data

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

2. Relevant equations

3. 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!

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2. Oct 9, 2011

### SammyS

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

3. Oct 9, 2011

### jegues

Doh.

Thank you.

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