When light passes through the interface between two media with different refractive indices, such as air and water, it can undergo several optical phenomena, including reflection, refraction, and transmission.
In the case of shining light at an angle into water, the light can indeed undergo reflection, but the majority of it is refracted and transmitted into the water. This is due to the difference in refractive indices between air and water.
When light encounters a boundary between two media with different refractive indices, such as air and water, it experiences a change in speed and direction. This phenomenon is known as refraction. The degree of refraction depends on the angle of incidence and the refractive indices of the two media involved.
According to Snell's law, which describes the relationship between the angles and refractive indices of incident and refracted light, the angle of refraction is determined by the refractive indices of the two media:
n1 * sin(theta1) = n2 * sin(theta2)
Where: n1 is the refractive index of the first medium (air), n2 is the refractive index of the second medium (water), theta1 is the angle of incidence, and theta2 is the angle of refraction.
In the case of light passing from air to water, water has a higher refractive index than air (approximately 1.33 for water and 1.00 for air). When light travels from a medium with a lower refractive index to a medium with a higher refractive index, it bends towards the normal line (an imaginary line perpendicular to the surface).
As a result, when light is shone at an angle into water, it is refracted and bent towards the normal line. This means that the light changes direction as it enters the water, and only a small portion of it is reflected back towards the air.
However, it's important to note that there is still a partial reflection occurring at the air-water interface. This reflection is known as "specular reflection," and it's responsible for the shiny appearance of the water's surface. The amount of light reflected depends on the angle of incidence and the difference in refractive indices between the media.
In summary, when light is shone at an angle into water, most of it is refracted and transmitted into the water due to the difference in refractive indices between air and water. Only a small portion of the light is reflected back towards the air, resulting in the partial reflection at the air-water interface.