This paper discusses the phenomenon on “Colored Lines”,which is the fourth question of the 2023 IYPT. When the light emitted by a light source shines on the surface of a compact disc (CD), a distinct bright stripe is produced at the center of the CD, and the color changes with the inclination angle of the CD. Based on this phenomenon observed in daily life, this paper investigates the optical phenomena on CDs through theoretical derivation, simulation, and the construction of an experimental system. The aim is to explore the optical phenomena on the CD, including the mechanism of the generation of the bright stripe, the grating constants of CD and DVD discs, the reason for the formation of a single bright stripe, and the specific influence of the inclination angle change on the color and position of the bright stripe.The research results are shown that the grating constants of CD and DVD discs are approximately 1.6μm and 0.74μm respectively. When diffraction occurs on CD and DVD discs, the bright stripe is always on the angular bisector of the observer and the light source. When the inclination angle of the CD is zero, the theoretical value of the wavelength of the diffracted light is 533.333nm, and the average value of the experimental measurement is 533.330 nm, which corresponds to green light. The color of the bright stripe has a quantitative relationship with the inclination angle of the CD. For green light, each incident angle corresponds to an interval of the inclination angle of the CD. When the horizontal incident angle=0.37rad and the inclination angle of the CD=0.9rad, the light intensity of green light is the maximum.
LI et al. (Sun,) studied this question.