angle of reflection equals angle of incidence

But that doesn't address the mechanism of reflection. If we start with the observation that i = r we can deduce that the energy and momentum of the reflected photons are conserved. My problem with BC's explanation is that it is back to front or possibly circular. It's a rubbish argument that stinks of philosophy, but it's the best I have at the moment! But we have implicitly defined and explicitly made a reflecting surface as locally symmetric. If the angle of reflection is not equal to the angle of incidence, there is something asymmetric happening at the surface. Depressingly, I am led to a reductio ad absurdam. Conservation of energy and momentum is an attractive starting point for a perfectly reflective mirror, but even the best-polished silver has a reflectance of around 95% at optical wavelengths, so conservation of energy doesn't really apply: 95% of visible photons are indeed reflected or retransmitted with the same energy as they arrived but up to 5% is lost as heat, and if the initial interaction is between a photon and an electron which then re-emits a photon, the momentum transferred to the electron is surely going to be distributed among other electrons, so the emission angle is not determined solely by the angle of incidence. If you reduce the intensity to a single photon it turns up somewhere as ordained by the model, but clearly cannot have spontaneously split into Evan's 'myriad of point sources' in order to work out where to go. The 'wavelet' model certainly gives the correct answer for a diffraction grating but only for very intense beams. If I start approaching this from a point of view of physics, it becomes very difficult to answer. This does not obey the 'traditional' law of reflection. If you modify the mirror so it is periodic (like a diffraction grating), there are multiple angles where the sources combine constructively, producing multiple outgoing waves. For an electromagnetic wave, this includes the current induced in the metal by the electromagnetic wave - Adding up the contributions from every point, the signal cancels everywhere except for an outgoing wave which obeys the law of reflection. When a wave hits a reflecting surface, you need to take into account the boundary conditions. This effect can be seen in the classic double-slit experiment, where both slits effectively become a point source of radiating waves. This myriad of point sources cancels out everywhere except for the solution where the wave moves ahead. Apply Maxwell's equations in a simulation package.Ī moving wave front can be modeled as a new wave radiating from every point on the wave front. The part of the wave moving parallel to the wall does not contribute to the reflected wave, so you end up with the traditional law of reflection. When a water wave strikes a wall, the horizontal amplitude becomes zero perpendicular the wall, but the vertical amplitude increases (conserving energy) - The energy stored in the increased amplitude is released by the water moving away from the wall, producing an outgoing reflected wave. The wave front will move ahead at a certain velocity when in a uniform medium. Or the molecules carrying sound, where the large-scale orderly motion of the sound wave (longitudinal wave) is superimposed on the general random movement of air molecules Water waves (transverse waves) also obey the angle of incidence = angle of reflection if they run into a vertical wall. The motion of the ball can be broken into two components of momentum: - One parallel to the cushion, which is not affected by the collision - One perpendicular to the cushion, which is reversed for an elastic (energy-conserving) collision - This produces a scenario where angle of incidence = angle of reflection - You could extend this to a photon striking a mirror. At least snooker gets around the gravity problem.

Particles like balls also obey angle of incidence = angle of reflection (if you ignore gravity, and the fact that balls tend to start spinning when they run into things).

Angle of reflection equals angle of incidence