Figure (a) below shows a lens with radius of curvature R = 250 mm lying on a fla

Question

Figure (a) below shows a lens with radius of curvatureR = 250 mm lying on a flat glass plate and illuminatedfrom above by light with wavelength = 543 nm.Figure (b) below (a photograph taken from above the lens) showsthat circular interference fringes (called Newton's rings)appear, associated with the variable thickness d of theair film between the lens and the plate. (a) Findthe difference in radius between adjacent bright rings (maxima)r = r59 -r58 and (b) the areabetween this adjacent bright rings. Assume that /R<< 1.

Explanation / Answer

given, radius of curvature = R =250mm=250*10-3m,wave length of light = =543*10-9m from the newton rings experiment r = (m+1/2)R plug m = 59 r59= ----m---(1) plug m = 58 , and , R values r58 = -----m---(2) r = eq(1) -eq(2) = ------m here rings are circular rings so area of circular ring =r2 r59 area =r592-----(3) r58, area=r582-----(4) A= eq(3) ----eq(4) =-------m2 r58, area=r582-----(4) A= eq(3) ----eq(4) =-------m2

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