* The two materials have the same refractive index. The refractive index is a measure of how much light bends when passing from one medium to another. If the refractive indices are equal, there will be no change in the speed of light as it transitions, and hence no bending.
* The light ray strikes the interface at a 90-degree angle. When light strikes the surface at a right angle (normal incidence), the light ray does not change direction as it enters the second medium. This is because the angle of incidence and angle of refraction are both zero.
Important Note: Even if the two materials have the same refractive index, light will still be reflected off the surface. This is because the two materials will always have a slightly different impedance, leading to some reflection of light energy.
Let me know if you'd like more details on any of these concepts!
