# Transition from one dielectric medium to another medium

1. Feb 3, 2016

### phoenix95

1. The problem statement, all variables and given/known data
A plane electromagnetic wave of frequency 5×1014 Hz and amplitude 103 V/m, traveling in a
homogeneous dielectric medium of dielectric constant 1.69, is incident normally at the interface
with a second dielectric medium of dielectric constant 2.25. The ratio of the amplitude of the
transmitted wave to that of the incident wave is ___________.

2. Relevant equations

3. The attempt at a solution
It should be 1 right? I mean passing from one dielectric medium to another would result in the change of phase velocity but not the amplitude??

2. Feb 3, 2016

### DrDu

You should also consider reflection.

3. Feb 3, 2016

### phoenix95

Would you please explain a little bit? I don't know how to apply that concept...

4. Feb 3, 2016

### DrDu

If the media are transparent, then the sum of the reflected and transmitted intensity must equal the incident intensity. The relative intensity of the transmitted and reflected intensity is dictated by the continuity of electric and magnetic fields at the boundary. Probably you were talking about this in class?

5. Feb 3, 2016

### phoenix95

No, this question is from one of the entrance examinations... I tried searching in the internet but I couldn't find any reasonable explanations...

6. Feb 3, 2016

7. Feb 3, 2016

8. Feb 3, 2016

### phoenix95

so the answer would be 0.857... Thanks a lot... The information was very useful...

9. Feb 3, 2016

### TSny

I don't believe this is the correct answer.

Equation (1227) of the link gives Et (but there is a misprint on the right of the equation where Et should be Ei).

Note that this equation is in terms of the indices of refraction of the materials, not the dielectric constants.

I guess you have to assume that the question is concerned with the electric field amplitudes and not the magnetic field amplitudes.

10. Feb 4, 2016

### DrDu

The index of refraction and the relative dielectric constant are related as $n=\sqrt{\epsilon_r}$. So n1=1.3 and n2=1.5 giving for the ratio of the transmitted to the incident electric field amplitude: 2n1/(n1+n2)=2.6/(1.3+1.5)=0.93.