I am in high school at the moment and I am revising a section on waves. I am slightly confused by some things in our notes, which I would like to ask about.
We looked at Young’s double slit experiment, and the following is my understanding: Both slits diffract the incident light, forming ‘semi-circle’ wavefronts. Where the two semicircles (one from each slit) intersect, they can interfere, forming a disturbance pattern on a screen placed there.
We then looked at diffraction grating, and I initially thought that the same thing was occurring there, only with far more semicircles. My professor, however, explained something different. He said that although the same kind of interference does happen, it is hard to see, and that the main fringes could only be seen with a lens. He then showed how parallel light rays could be focused, and then would either form a bright fringe or a dark fringe, depending on whether the path distance was an integer or half-integer wavelength apart.
My professor said that, at our level, there is a kind of distinction between interference fringes (like what is happening in Young’s experiment), and diffraction fringes (like with the ‘main part’ of diffraction grating).
I can’t seem to understand the difference, and especially what determines which of the two is the dominant one in any given experiment. I hope I have made myself clear, because I find it very difficult to explain my confusion - feel free to ask for any clarification, and thank you very much for your answers, it means a lot.