Understanding Light Wave Properties When Changing Medium

When a wave, such as a light wave, travels from one medium to another, several of its properties can change. The question asks which property remains the same when a light wave travels from air to water.

Let's consider the key properties of a wave: frequency, velocity (or speed), and wavelength.

• Frequency (\(f\)): Frequency is the number of wave cycles that pass a point per unit of time. It is determined by the source of the wave. When a wave moves from one medium to another, the source is still producing vibrations at the same rate. Therefore, the frequency of the wave does not change.
• Velocity (\(V\)): Velocity is how fast the wave travels through the medium. The speed of light changes when it moves from one medium to another. This change in speed is related to the refractive index of the media. Light travels slower in a denser medium like water compared to a rarer medium like air.
• Wavelength (\(\lambda\)): Wavelength is the distance between two consecutive crests or troughs of a wave. The relationship between velocity, frequency, and wavelength is given by the equation: \(V = f\lambda\).

We know that the velocity (\(V\)) changes and the frequency (\(f\)) remains constant when light moves from air to water. Based on the equation \(V = f\lambda\), if \(V\) changes and \(f\) is constant, then the wavelength (\(\lambda\)) must also change. Specifically, since light slows down in water (velocity decreases) and frequency is constant, the wavelength must decrease proportionally.

So, when a light wave travels from air to water:

• Velocity changes (decreases).
• Wavelength changes (decreases).
• Frequency remains unchanged.

Therefore, the property that remains unchanged when a light wave travels from air to water is frequency.