Light wavelegth strikes a pane of glass of thickness T and refractive index N, a

Question

Light wavelegth strikes a pane of glass of thickness T and refractive index N, as showin in the figure. Part of the beam is reflected off the uppers surface of the glass, and part is transmitted and then reflected off the lower surface of the glass

T=Wavelthgn/2

2T=Wavelentgh/2

T=Wavelenth/2N

2T=wavelength/2N

Light wavelength strikes a pane of glass of thickness T and refractive index N, as showing in the figure. Part of the beam is reflected off the uppers surface of the glass, and part is transmitted and then reflected off the lower surface of the glass

Explanation / Answer

T = wavelength/(2n)

The reason: The top reflection produces a phase reversal since n(air) < n(glass). The bottom reflection does not produce a phase reversal since n(glass) > n(air). Thus the extra path length 2T must provide a 1-wavelength, or lambda(glass), phase shift for destructive interference with the 1/2-wavelength shift of the top reflection. Lambda(glass) = lambda(air)/n.

Thus 2T = lambda(glass) = lambda(air)/n = lambda/n, so T = wavelength/(2n)

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