Reflection loss and refractive index

[Puchinita5]

Homework Statement

"Calculate the reflection loss when a beam of radiant energy passes through an empty quartz cell assuming the refractive index of quartz is 1.55"

Homework Equations

I/I_i = ((n2-n1) / (n2+n1))^2

The Attempt at a Solution

I'm taking the refractive index through the empty cell to be 1 (is that right?)I/I_i = ((n2-n1) / (n2+n1))^2
= ((1.55-1)/(1.55+1))^2 = 0.047 or 4.7%

The answer in the back of the book is 17.3 %

what am i doing wrong?

 

[Ninty64]

If the light is passing through the quartz, how many times does it get refracted?

You are right in assuming the refractive index inside is 1.