After heavy rain, an engine oil was accidentally dropped on a wet concrete road. People observed that the color of the of floating on water appear to be bright red when viewed almost perpendicularly on the surface, see the figure. If light falls perpendicularly on the thin oil film and the wavelength of red light in vacuum is = 650 nm, calculate the nonzero minimum thickness t of the fllm.

After heavy rain, an engine oil was accidentally dropped on a wet concrete road. People observed that the color of the of floating on water appear to be bright red when viewed almost perpendicularly on the surface, see the figure. If light falls perpendicularly on the thin oil film and the wavelength of red light in vacuum is = 650 nm, calculate the nonzero minimum thickness t of the fllm.