Hey everybody, 1. The problem statement, all variables and given/known data: I came across a question discussing Young's Double Slit interference and was wondering how come when we diffract white light through the slits it gives us a central antinodal fringe that is also white? The question itself came in parts firstly considering monochromatic light diffracting and interfering through double slits. The section I couldn't answer states "The monochromatic illumination is replaced by sunlight. Explain how this will assist the experimenter to determine the position of the new central maximum bright fringe" 2. Relevant equations: The small angle approximation and the diffraction grating formula 3. My attempt: Obviously when you do the experiment with monochromatic light all the fringes will be the same colour however, my understanding is that white light actually consists of all the different frequencies of visible light and hence these diffract at different angles to produce a spectra of colour. But when I googled an image for the interference pattern of white light through a diffraction grating all the pictures show the central fringe is white flanked by overlapping coloured fringes (Which must answer the physical question stated in the book about how the experimenter would be able to determine the position of the central maximum - by spotting the white fringe). But the answer doesn't go on to explain why this fringe occurs and I can't understand or find a reason or an equation that explains why this central fringe isn't a spectrum of colours as well? I assume this must have something to do with path difference of the light waves. At the central antinode there is no path difference so does that mean that the waves of the different frequencies add to give white light. That would be my guess but the answer in the book is very vague and doesn't confirm this at all.