FM radio and green laser light are the same phenomenon, 5.6 million× apart in frequency. End to end, this bar covers a ten-quadrillion-fold range. Drag a marker.
Visible light, magnified:
Glass slows every frequency on this strip by a slightly different amount, so each one bends through a slightly different angle, and white light fans out into exactly the band drawn above. Newton did it with a prism in 1666 and named seven colours, but seven was taste: the band is a continuum, one colour per frequency, no seams.
→ RUN THIS EXPERIMENT IN THE LIGHT LABDo you even know what a CD looks like up close, in real life? The Light Lab has one: tilt it under a lamp, then dive forty-thousand-fold into its surface to the micrometre-sized pits that build the rainbow, and watch the light itself sort into colours.
→ EXPLORE THE PHYSICSEach droplet refracts sunlight on the way in, reflects it off the back, and refracts it again on the way out. Red exits at about 42 degrees from the antisolar point and violet nearer 40, which is why the bow is a band and red is on the outside. Sun behind you, mist in front, look at your shadow's head height.
→ RUN THIS EXPERIMENT IN THE LIGHT LABAir molecules scatter light in proportion to the fourth power of its frequency, so the blue end of this strip scatters roughly ten times as strongly as the red end. Look anywhere but at the sun and scattered blue is what reaches you. At sunset the light crosses so much air that the blue has been scattered away en route, and what survives the trip is the red. Try it: drag the sun down.
No pigment, no prism, no grating. A soap film is a few hundred nanometres thick, so light reflecting off its back surface returns a fraction of a wavelength behind light reflecting off the front. Colours whose waves land in step show; colours that land out of step cancel. The swirl is the thickness of the film, made visible, and the black patch that spreads just before it pops is the film gone thinner than any colour can survive.
→ WATCH ONE DRAIN IN THE LIGHT LABA hologram is not a picture of a thing. It is a recording of an interference pattern: the light from the object met a second beam at the plate, and where the two arrived in step they wrote a bright fringe, where out of step a dark one. Lighting those fringes again hands the original wave back, direction and all, which is why the scene has depth and shifts as you move. Cut a photograph in half and half the scene is gone; cut a hologram in half and you have only stepped back from the window.
→ RECORD ONE IN THE LIGHT LABFor scale: point a beam at an apple. Dial one is frequency. The eventful stretch is the high end, so this bar is zoomed; the strip shows where the window sits on the full spectrum:
Dial two is power, held on the apple for 60 s:
The two dials are the whole lesson. Frequency decides what each photon can do: nudge, excite, break a bond, or ionize. Power times time decides how much arrives. Pour megawatts into radio and it cooks. A gamma trickle cannot warm a thing, yet every photon still ionizes. That is why your router is harmless and a sterilizer plant is not. Please do not eat any irradiated apples!
Everything warm glows. Dial three is temperature. Every object above absolute zero radiates across this whole bar, and one number decides where the glow peaks:
Planck's law, drawn per unit wavelength and scaled to its own peak; the marker sits at Wien's λmax = 2.898 mm·K ÷ T. Counted per unit frequency instead, the peak lands 1.76× lower, which is why the cosmic microwave background is quoted both at 1.06 mm and at 160 GHz: the same glow, sliced two ways. Radiated power is Stefan-Boltzmann, σT⁴, for a perfect emitter.
All wind is reprocessed sunlight. The Sun delivers energy to Earth purely as electromagnetic radiation. It lands unevenly: equator vs poles, land vs sea, day vs night. The uneven heating makes pressure differences, and air falls down those gradients. Roughly 1 to 2% of incoming solar power ends up as wind. So every gust is EM energy that arrived as photons, thermalized, and got converted into moving air. A wind turbine is, with a couple of steps in between, solar powered.
And we measure wind with EM. Doppler weather radar bounces microwaves off raindrops and reads the frequency shift of the echo: moving droplets compress or stretch the returning wave, and that shift is the wind speed. Lidar does the same trick with laser light off dust and aerosols; satellite scatterometers read ocean wind from how microwaves scatter off wind-roughened water. Wind has no EM signature of its own, so we interrogate it with EM and read the answer in the Doppler shift.
Everything on this site runs the real physics in miniature: Planck's E = hf behind every readout, Snell and dispersion in the prism, the grating equation on a real 1.6 µm track pitch in the CD, the 42° droplet cone, Rayleigh's 1/λ⁴ in the sky. Illustrative in scale, honest in mechanism; if a number here disagrees with your textbook, trust the textbook and tell us. Studio lighting HDRI by Poly Haven (CC0).
Built by Amy Robinson Sterling @amyneurons, with Fable and Sol.