When the slit is very wide, the width of the slit is much larger than the wavelength of the light, and the diffraction phenomenon is extremely insignificant. The light propagates along a straight line, producing a bright line on the screen that is equal to the width of the slit; but when When the width of the slit is adjusted to be very narrow, comparable to light waves, the light will obviously deviate from the straight-line propagation direction after passing through the slit, and will illuminate a fairly wide area on the screen, and alternating light and dark diffraction stripes will appear. The smaller the slit, the smaller the slit. The larger the diffraction range, the wider the diffraction fringes. But the brightness is getting dimmer.