I have a few questions: 1. Most CD players use laser light in the red portion of the spectrum. What changes would be required in the manufacturing of CDs if blue light were to be used? 2. A student performs Young's double-slit experiment using a slit separation of 21.6um. A screen is placed 2.50m from the centre of the sources such that a point on the fifth nodal line is 37.5cm from the centre of the interference pattern. Find the wavelength of the light used and identify its colour. -> I was going to use the equation dXn/L = (n-1/2)lambda There's also the equation delta x = L x lamda / d i don't know which equation to use. I know that d = 21/6um, L = 37.5cm but what's 2.50m? 3. A two-point source interference pattern in a ripple tank with two sources operation in phase: A point on the eigth nodal line is 1.25m from the centre of the two sources and 48.0cm from the perpendicular bisector of the two sources. If the source separation is 2.75cm, find the wavelength of the waves. -> I'm not sure what 1.25m and 48.0cm represent. and one quick question. if one wave crest takes 2.0s to travel the 35.0m width of the pool, the speed is just v = 35.0m / 2.0s right? ( this might be a stupid question....i know...;;) If you can help me with any of these questions, I would greatly appreciate it :) Thanks!