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To produce a minimum reflection of wavelength near the middle of visible spectrum (550nm) how thick should a coating of mgf2 \left ( \mu =1.38 \right ) be vacuum coated on glass surface?

Option: 1

10^{-10}m^{}}


Option: 2

10^{-8}m


Option: 3

10^{-7}m


Option: 4

10^{-11}m


Answers (1)

best_answer

As we learn

Thin Film Interference in reflected light -

For normal incidence 

For destructive interference

  2\mu t=\left ( 2n+1 \right )\frac{\lambda }{2} \ \ where \ \ n=1,2,3....

To produce a minimum reflection, destructive interference should happen

So use 2\mu t=\left ( 2n+1 \right )\frac{\lambda }{2} \ \ where \ \ n=1,2,3....

at n=0         

  2\mu t=\frac{\lambda }{2}                 

 t=\frac{\lambda }{4\mu}=\frac{550*10^{-9}}{4*1.38}=100nm                        

        t=10^{-7}m                                                        

 

Posted by

Ritika Harsh

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