Question

A certain type of laser emits light that has a frequency of 4.9 x 1014 Hz. The light, however, occurs as a series of short pulses, each lasting for a time of 2.9 x 10-11 s. The light enters a pool of water. The frequency of the light remains the same, but the speed of light slows down to 2.3 x 108 m/s. In the water, how many wavelengths are in one pulse

Answer 1

N = 1.42 × 10⁴ cycles

Step-by-step explanation:

Given that:

frequency f = 4.9 × 10¹⁴ Hz

Time = 2.9 × 10⁻¹¹ s

Speed = 2.3 × 10⁸ m/s

Recall that:

wavelength
`\lambda = (c)/(f) \\ \\`

Horizontal distance
`\Delta x = ct`

Number of wavelengths
`(N) = (\Delta x)/(\lambda)`

`N = (ct)/(c/f) \\ \\ N= ft`

N = (4.9 × 10¹⁴ cycles/s) (2.9 × 10⁻¹¹ s)

N = 14210

N = 1.42 × 10⁴ cycles