Physics - Wave Optics Question with Solution | TestHub

The distance between successive wavefronts represents the wavelength $\lambda$ of the wave.

When a wave passes from a denser medium to a rarer medium, its speed $v$ increases.

The frequency $f$ of the wave remains unchanged during refraction.

Using the relation $v=f\lambda$, since $v$ increases and $f$ is constant, the wavelength $\lambda$ must increase.

Therefore, the distance between successive wavefronts increases.

Answer: increases.