Answer: d. The waves must have the same frequency.
Explanation:
Interference is a phenomenon that occurs in all types of waves and consists of the superposition (constructive or destructive) of two or more waves to form a resulting wave of greater, lesser or equal amplitude.
The occurrence of this phenomenon depends fundamentally on the wavelength [tex]\lambda[/tex], the amplitude and the relative distance between the waves (phase difference).
In this sense, to observe a wave interference pattern from two sources, the following conditions must be met:
-The sources must be coherent, that is, they must maintain a constant phase difference.
-The sources must be monochromatic, that is, they must have exactly the same wavelength.
-The sources must have the same amplitude.
However, it is not necessary that the waves have the same frequency [tex]f[/tex], the interference pattern will be observed regardless of whether the initial waves have the same frequency or not.
At this point, it is necessary to explain the following:
There is an inversely proportional relationship between frequency and wavelength:
[tex]f=\frac{v}{\lambda}[/tex]
When a wave passes from one medium to another, its wavelength and speed [tex]v[/tex] change, but its frequency does not.
