Physics on light

Question

You observe light being refracted though a strange substance. Find the speed of the light in this substance if it has a wavelength of 4.0*10^-7 and a frequency of 3*10^14. Make sure your answer goes to one decimal place

Answer 1

You really need to pay attention to the units.. This problem is trivial if you do so as wavelength is in meters/cycle and frequency is in cycles per second (you can treat cycles as implied in which case you have m and 1/sec). It is clear to multiply these so cycles cancel and you get m/s. (1.2 x 10⁸ m/s)