Question

I already have the answers...I just need someone to explain to me the logic behind the work done to obtain the answer if that makes sense lol.

  1. A laser beam shines along the surface of a block of transparent material. Half of the beam goes straight to a detector, while the other half travels through the block and then hits the detector. The time delay between the arrival of the two light beams at the detector is 6.15 nanoseconds . The distance is 2.50 meters. What is the index of refraction of this material?
  2. The answer is 1.74. When I looked online for clarification if what I was doing was correct it was telling me to use v=d/t to find the velocity in air and velocity in the material and to divide them both. Which doesn't quite make sense to me. I found one velocity to be 4.065*10^8 m/s but how do I find the other? And why do I divide them to get the index of refraction?

  3. Light with a frequency of 5.95×1014 Hz travels in a block of glass that has an index of refraction of 1.52. A.- What is the wavelength of the light in vacuum? B.- What is the wavelength of the light in the glass?

Part A I got a correct answer of 5.0410^-7m. For Part B I received the correct answer of 3.3110^-7m. But why do I divide the answer to part A by the index of refraction to find the wavelength for part B?

Any help would be greatly appreciated!