When a wave crosses from one medium to another where the wave speed is slower. The frequency of the wave is unchanged. The wavelength: a) increases b) decreases c) stays the same d) No answer text provided.

a. Its wavelength decreases

Explanation:

This is because from refractive index, n = v₁/v₂ = fλ₁/fλ₂ where v₁, v₂ and λ₁,λ₂ are the wave speeds in medium 1 and 2 and wavelengths in medium 1 and 2 respectively and f is the frequency of the wave.

If v₂ is the slower speed, it follows that

v₂ = v₁/n

fλ₂ = fλ₁/n (since f is constant)

λ₂ = λ₁/n

Since the wavelength λ₁ is reduced by a factor n, λ₂ thus decreases.

So the wavelength decreases in the slower medium

A). Increase

Explanation:

Refraction is the change in direction of waves that occurs when waves travel from one medium to another. Refraction is always accompanied by a wavelength and speed change. Diffraction is the bending of waves around obstacles and openings. The amount of diffraction increases with increasing wavelength.

Frequency doesn't change because it depends on travelling of waves across the interface. But speed and wavelength change as the material on the other side may be different, so now it might have a longer/shorter size of wave and so the number of waves per unit time changes.