In a physics lab, light with a wavelength of 550 nm travels in air from a laser

Question

In a physics lab, light with a wavelength of 550 nm travels in air from a laser to a photocell in a time of 17.5 ns. When a slab of glass with a thickness of 0.820 m is placed in the light beam, with the beam incident along the normal to the parallel faces of the slab, it takes the light a time of 20.8 ns to travel from the laser to the photocell. What is the wavelength of the light in the glass? Use 3.00 times 10^s m/s for the speed of light in a vacuum. Express your answer using two significant figures.

Explanation / Answer

speed = wavelength * frequency

3 * 10^8 = 550 * 10^-9 * frequency

frequency = 5.454 * 10^14 Hz

speed = distance / time

speed = 0.82 / (20.8 * 10^-9)

speed = 39423076.9231

39423076.9231 = 5.454 * 10^14 * wavelength

wavelength = 7.228 * 10^-8 m

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