Question

Which of the following conditions is not necessary to observe an interference pattern between two sets of waves?

Answer 1

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 $\lambda$, 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 $f$, 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:

$f=\frac{v}{\lambda}$

When a wave passes from one medium to another, its wavelength and speed $v$ change, but its frequency does not.

Answer 2

Answer:

d. The waves must have the same frequency.

Explanation:

We can observe two waves that have interference between them and they create a pattern that can be destructive or constructive, in order for us to see them the waves have to meet three conditions: They need to have the same wavelenght, they must have a constant phase difference, and the same amplitude, otherwise they would interfere with eachother, the only that is not necessary is that they must have the same frequency.