Hi and thank you for viewing this post. I'll begin with the question from the text book; Q: An electromagnetic radiation has a frequency of 5.00 x 10^14 Hz. a) Calculate its wavelength in a vacuum, in meters and nanometers. b) Calculate its wavelength in water. c) Is this radiation visible? If so, what is its colour? d) What is the index of refraction of a medium in which the speed of this radiation is 2.54 x 10^8 m/s? e) Where would you encounter this radiation in your daily life? and here are my attempts to the above questions; A: a) given that the speed of light in "vacuum" is 3.00 x 10^8 m/s, (not sure how to type-in the wavelength sign) wavelength = 3.00 x 10^8 m/s / 5.00 x 10^14 Hz Then it comes out to be, 6.00 x 10^-17 m which also equals to 600nm. b) given that the speed of light in "water" is 2.2 x 10^8 m/s, wavelength = 2.2 x 10^8 m/s / 5.00 x 10^14 Hz which turns out to be 4.4 x 10^-7 m, and 440 nm. c) I had a confusion because I wasn't really sure whether the question was asking about the radiation in vacuum or in water (Sorry this is an independent study course so there aren't any teachers whom I can contact). So, I gave the answer for both situations. Orange(590-610nm) for a), and Violet(400-450nm) for b). d) Again, confusion from the question c.. not really sure whether to use orange(neon gas) or violet(mercury vapour) as the source. According to the textbook the equation looks like this, n=c/v (n=absolute index of refraction, c=speed of light, v=speed of light in substance) so am I looking to solve for the variable n? e) Our ordinary main way to gather information about the world. So it would be greatly appreciated if anyone could read this over and correct me any wrongs. Any suggestions or advice are also appreciated, Thanks again!