optics q

[inaccensa]

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a soap film of thickness "t" is surrounded by air and is illuminated at near normal incidence by monochromatic light with wavelength "w"With respect to "t" in the film what thickness will produce maximum constructive interference?
waves in phase = constructive 2t=mw/n m=0,1,2
waves out of phase =constructive --> 2t = (m+.5)w/n m=0,1,2

I thought both waves will be in phase, but it doesnt seem so

 

[inaccensa]

never mind, I realized my mistake

 

[geeyouknit]

a soap film of thickness "t" is surrounded by air and is illuminated at near normal incidence by monochromatic light with wavelength "w"With respect to "t" in the film what thickness will produce maximum constructive interference?
waves in phase = constructive 2t=mw/n m=0,1,2
waves out of phase =constructive --> 2t = (m+.5)w/n m=0,1,2

I thought both waves will be in phase, but it doesnt seem so

Can you explain this? Doesn't constructive interference imply two waves? There only seems to be one wave? I just don't seem to understand the question in general.

Thanks

 

[inaccensa]

Can you explain this? Doesn't constructive interference imply two waves? There only seems to be one wave? I just don't seem to understand the question in general.

Thanks

Well, its like a bubble suspended in air. A wave of light in air, hits the air/soap interface and reflects while changing phase. The same wave of light is refracted in the film and reflects at the soap/air interface, but doesnt change phase, since refractive index of soap is greater than air. refracted waves dont change phase, so you get two waves out of phase. Just plug the numbers in the formula🙂