Percentage of light transmitted by glass samples

Can any one help me with the answers to the question below?

A sample of glass has a refractive index of 0,99. If the glass is non selective, calculate the percentage of light transmitted by samples of 12mm, 25mm, and 75mm thick respectively

Thanks
Clive

 

Log in or Sign up to hide all adverts.

Unless memory is terribly wrong, the conventional definition of the refractive index is ratio of speed of light in vacuum (or air for practical reasons) to light speed in the material. Thus it is always a number great than unity.

Second point is that in "clear" glass, will lose most of the light normally incident upon it by two reflections - one at front and one at rear or leaving glass air glass interface. Typically each has about 4% reflected. Less will be transmitted when the incident rays are not normal to the surface. Thus your three thicknesses will have approximately the same percentage transmitted, if the class is “clear.”

The magnitude of the surface reflection at any interface can be calculated from Maxwell's equations but for normal incidence you should be able to search and find the results. (It is simple expression in "n" the refractive index.) Read any good optics book. It will give the full funtional equation for polarization and all incident angles. I.e. results from Maxwell's equations. (Years ago I solved those equations for that relationship – it is a "boundary value" problem. That solution does not need to assume normal incidence, but if not normally incident, then each polarizaion must be treated separately)

At an angle of incidence, called the Brewster's angle, 100% of one polarization is reflected at the front surface (and a slight amount of the other reflection is too) so less than half of incident un-polarized light will even enter the glass.

Also if the front and back surfaces are not parallel, it is possible for rays inside the glass to be totally internally reflected rather than exit, but this is not the normal condition.

 

Log in or Sign up to hide all adverts.

As Billy T said, refractive indexes for materials must always be greater than 1 (the index for a vacuum is 1), so this calculation wouldn't make physical sense anyway

 

Log in or Sign up to hide all adverts.