Here's why:
* Refraction: When light passes from one medium to another (like air to water or air to glass), it changes direction. This bending of light is called refraction.
* Scattering: The change in direction of light due to refraction can cause the light to scatter, making it visible.
* Examples:
* You can see a laser beam in the air because the air molecules scatter the light.
* You can see a beam of sunlight through dust particles in the air because the dust scatters the light.
In summary, a beam of light becomes visible when it encounters a medium that causes it to change direction and scatter.
