Which of the following conditions is not necessary to observe an interference pattern between two sets of waves?
a) the waves must have the same wavelength.
b) the waves must have a constant phase difference.
c) the waves must have the same amplitude.
d) the waves must have the same frequency.

To achieve an interference pattern, we must have two coherent wave sources. For coherence, the waves must have the same frequency and either have no phase difference or a constant phase difference.

For two waves traveling in the same medium, having the same frequency implies having the same wavelength by v = fλ where v = velocity, f = frequency, and λ = wavelength.

An interference pattern requires all of the above conditions except for having the same amplitude.

Choice C

the answer is a 3.8cm

explanation:

adding a(n) to an electric circuit would increase the magnetic field around a wire;

b. solenoid

a solenoid is a type of electromagnet whose purpose is to generate a controlled magnetic field.

if the purpose of the solenoid is instead to impede changes in the electric current, a solenoid can be more specifically classified as an inductor rather than an electromagnet.