Destructive interference of the reflected light, Physics

Assignment Help:

It is desired to lessen the reflection of light by the outer surfaces of the objective lenses of a pair of binoculars. These surfaces are the foremost surfaces that light hits on entering the binoculars. The lenses are prepared of crown glass. To lessen the reflection the lenses should be coated with a transparent medium of the right thickness and of the right index of refraction. For utmost destructive interference of the reflected light the value of the index of refraction of the coating.

Answer:

Acceptable we want to put a quarter-wave thickness of optical coating on the lens to cause a path difference of half a wavelength consequently that we get destructive interference between the light path 1 light that reflects off the first interface (the air/coating interface) and the light path 2 light that reflects off the second interface (the coating/glass interface).

What we typically don't talk about in discussing thin-film interference is the amplitudes. However to get the most destructive interference where they do interfere we want the amplitudes to be the same. Then a crest of path 1 light is entirely cancelled by a trough of path 2 light. Now the bigger the dissimilarity between the indices of refraction of the two media on either side of an interface the greater the amount of reflection from that interface.

Presume we had the index of refraction of the coating exactly midway between that of air and that of the crown class. Additional suppose that 10% of the light is reflected off each surface. The value isn't important but the fact that both values are the same is reasonable since the difference ncoating-nair is under the given circumstances the same as the difference nglassncoating. If 10% is replicated off the first surface only 90% gets through. After that 10% of that 90% which is only 9% of the original intensity is reflected off the second surface and only 90% of that or 8.1% of the original intensity makes it back out through the first surface. Therefore where the light from the two paths joins together again back in the air after reflection we have 10% of the original intensity interfering with 8.1% of the original intensity consequently the cancellation will not be perfect (even if the coating is of the perfect thickness). If we reduce the index of refraction of the coating a little bit making it a little closer to the index of refraction of air we decrease the reflection at the first surface as well as increase the amount that gets through that surface and the percentage of that amount that is reflected off the second surface and then makes it back through the first surface. With the correct choice of the coating index of refraction extrapolating upon the given example we can bring that 10% down and the 8.1% up just enough to have them meet in the middle. If they are both equivalent we are able to get perfect destructive interference.

Therefore to maximize the destructive interference of the reflected light we need the index of refraction of the coating to be in between the nair and nglass, and we need it to be a little bit closer in value to nair than it is to nglass.


Related Discussions:- Destructive interference of the reflected light

Deriving a working equation, Hi, i am max a physics student working on a pr...

Hi, i am max a physics student working on a project. Can you help me derive a working equation from faradays equation and ampere equation in rectangular coordinates? I am trying to

Calculate the total amount of energy transfer by heat, A rigid tank primari...

A rigid tank primarily contains 3 kg of air at 500 kPa, 290 K. The tank is connected by a valve to a piston-cylinder assembly oriented vertically and consisting of 0.05 m³ of air i

Perpendicular bisector , Determine the potential and field due to a short d...

Determine the potential and field due to a short dipole of dipole moment 5.0 X 10 -16 coulomb-cm at a point distant 1 cm from it. (a) on its axis (b) on its perpendicular bi

Explain the molecular theory of surface tension, (i)  On the average, parti...

(i)  On the average, particles are separated by a distance of the order of 10-10 m and exert a force of attraction of the order of 10-11 N on each other. (ii)  The force of atta

Special resistor materials: constantan, Constantan: Constantan is a copper...

Constantan: Constantan is a copper-nickel alloy. The amount of nickel in constantan is 40%. Properties: 1.      It is silver like appearance. 2.      Its electrical res

Infra-red detectors and optic lens, Infra-Red (IR) Detectors:   An IR ...

Infra-Red (IR) Detectors:   An IR detector has an impedance of Z= (400+j200) ?  . During design  tests the detector  current  is measured  as  4  µA. What  is  the output v

Barrier potential in a p-n junction, Barrier potential in a P-N junction is...

Barrier potential in a P-N junction is caused by (A) Thermally generated electrons and holes. (B) Diffusion of majority carriers across the junction. (C) Migration

Define transverse waves , Particles of the medium implement simple harmonic...

Particles of the medium implement simple harmonic motion about their mean position in a direction perpendicular to the direction of propagation of wave motion. (i) It goes in th

Explain the types of x-rays, Depending upon the penetration power, there ar...

Depending upon the penetration power, there are two parts of X-rays Hard X-rays More penetration power More frequency of the order of ≈ 1019 Hz Lesser wavelength range

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd