Frequency is the number of waves that pass a point in one second. When a wave goes from one medium to another, the frequency remains the same. This is a fundamental property of waves known as the principle of frequency invariance.
Amplitude refers to the maximum displacement of a particle from its equilibrium position in a wave. When a wave goes from one medium to another, the amplitude may change, particularly if there is a change in the wave's energy due to reflection, refraction, or other factors. However, the question asks about "no change," so amplitude may not necessarily remain the same in all cases.
Wavelength is the distance between two consecutive points in a wave that are in phase (e.g., two consecutive crests or troughs). When a wave goes from one medium to another, the wavelength can change due to a change in the wave's speed (velocity) in the new medium. This is described by Snell's law for refraction.
Velocity refers to the speed and direction of wave propagation. When a wave goes from one medium to another, the velocity typically changes, as waves can travel at different speeds in different materials. The change in velocity is often described by Snell's law for refraction.
Option A is correct. Frequency is the number of waves that pass a point in one second. When a wave goes from one medium to another, the frequency remains the same. This is a fundamental property of waves known as the principle of frequency invariance.