What Is The Speed of Dark?

Shadows moving faster than light?

 

Hewitt-Drew-it! PHYSICS 86. Wave Interference

Interference for waves in general, with emphasis on sound, beats, and anti-noise technology.

 

Michelson Interferometer

In this setup, an interferometer is used to measure the wavelength of laser light. The incident beam is split into two paths, recombined, and projected on a screen. When one of the path lengths is varied, the interference pattern on the screen changes. By measuring the distance that a path length must be changed in order to achieve the original interference pattern, one can determine the wavelength of the incident light.

 

MIT 8.02 Electricity and Magnetism Lecture 33

Double-Slit Interference, interferometers.

 

Single Photon Interference

What happens when single photons of light pass through a double slit and are detected by a photomultiplier tube? In 1801 Thomas Young seemed to settle a long-running debate about the nature of light with his double slit experiment. He demonstrated that light passing through two slits creates patterns like water waves, with the implication that it must be a wave phenomenon.

 However, experimental results in the early 1900s found that light energy is not smoothly distributed as in a classical wave, rather it comes in discrete packets, called quanta and later photons. These are indivisible particles of light. So what would happen if individual photons passed through a double slit? Would they make a pattern like waves or like particles?

Other Veritasium videos

 

3 Physics Experiments that Changed the World

Cavendish experiment (gravity), Young double-slit experiment (interference of light) and Rutherford gold foil experiment (atomic nucleus).

Other Sci-Show videos

How to Measure the Width of a Hair With a Laser!

Exactly how small is a hair's breadth? Measure it for yourself with nothing more than a laser pointer and a tape measure!

Other Frostbite Theater videos

Microwave Fabry-Perot interferometer

Microwaves are a form of electromagnetic wave, just as visible light is. Being a way, it can experience interference, just as light can, but having a wavelength on the order of an inch long, in this demonstration, it is much easier to observe the interference. In this video, we see how a Fabry-Perot interferometer works.

 

Surface White Light Interference Microscopy

Demonstration of Surface Profile Microanalysis.

Young's Double Slit Demo

Using a yellow rope and red tape to demonstrate Young's Double Slit equation.

 

Sound Wave Interference (MIT Demo)

Two speakers, mounted on the table and facing each other, are driven by a function generator. A microphone is introduced between the speakers and the sound waves are displayed on an oscilloscope. This demonstrates the effect of interference and the resulting phase shift on sound waves over a fixed distance. Three different frequencies are demonstrated; 880Hz (A5), 440Hz (A4) and 523.3Hz (C4).

Other demonstrations from MIT

Beats animation

2 waves (green and cyan) have slightly different frequency. The amplitude of the resultant wave (yellow) varies with time.

Other animations by Yves Pelletier

Beats demo (tuning forks)

Two tuning forks with slightly different frequencies produce beats.

Thin Film Interference: anti-reflecting coating

This animation illustrates destructive thin-film interference (which can be applied to anti-reflecting coating). The yellow wave is incident light (in air). When it reaches a substance with a higher refractive index (here n = 1,5), part of the light is reflected transmitted (shown in yellow: the wavelength becomes shorter) and part of the light if reflected with a 180° shift(shown in green). If the third medium (at the bottom) has a refractive index higher than 1.5, part of the transmitted light is reflected with a 180° shift (shown in pink). The reflected waves cancel each other (destructive interference) if the thin film has a proper thickness.

Other animations by Yves Pelletier