Hey Siri, what's reflection? Reflection is the change in direction of a wave front and an interface between two different media so that the wave front returns into the medium from which it originated. Common examples include the reflection of light, sound in water waves. The law of reflection says that for specular reflection the angle at which the wave is inserted on the surface equals the angle at which it is reflected. Mirror's exhibit specular reflection, in acoustics, reflection causes echoes and is used in sonar. But what is reflection? The law of reflection with Caitlin Cerillo and John Batheson. Well gosh, look at all those reflections. But how do they work? Let's ask science. The law of reflection states that an incident light ray at a certain angle theta from the normal, that is, the line perpendicular to the plane of reflection, will be reflected at the same angle from the normal on the same plane. For example, this light ray incident on a plane mirror with incident angle 45 degrees from the normal is reflected off of the mirror at 45 degrees from the normal or pi for 4 radians. When the incident angle is changed to 30 degrees from the normal, the reflected angle is also 30 degrees from the normal or pi for 6 radians. The same rule applies when the incident ray is angled 70 degrees from the normal. The reflected ray is also measured to be 70 degrees or 7 pi over 18 radians. Huygens principle concerns wave fronts which are perpendicular to the ray. When the wave front strikes a medium, it creates wavelengths that expand in all directions at a rate depending on the velocity of light in that medium. A new wave front is created which is tangent to each wavelength. When the reflection occurs, the velocity of propagation is the same between the wavelengths forming the incident ray and those forming the reflected ray. In such a case, theta i equals theta r. Hey Siri, I just learned that for reflection, theta incident equals theta reflected. I didn't quite get that. Oh Siri.