Discoveries That Changed Physics Pixel Sticker Sheet

11 pixel-art physics stickers on one A5 (5.83″ × 8.27″) white kiss-cut sheet: Discoveries That Changed Physics. Every character below has its own sticker page with the full physics panel.

Fogplate

Henri Becquerel suspected that uranium salts, made to glow by sunlight, might give off X-rays. Paris stayed cloudy in late February 1896, so he put plates wrapped in black paper, with uranium salt on top, in a drawer. On 1 March he developed them anyway and found strong images: the uranium emitted penetrating rays with no sunlight at all (Comptes rendus 122, 501, 1896). It was radioactivity.

uranium → rays, no light needed

uranium salt: potassium uranyl sulfate in his first tests; plate: photographic plate wrapped in black paper

Corpuscle

In 1897 J. J. Thomson crossed electric and magnetic fields over a cathode-ray beam (“Cathode Rays”, Phil. Mag. 44, 293). He tuned them so the beam ran straight, which gives its speed, v = E/B; then the deflection from one field alone gives the mass-to-charge ratio. The result was about a thousand times smaller than for the hydrogen ion, whatever the gas or electrode metal. He called the particles corpuscles: we call them electrons.

v = E/B

v: beam speed (m/s); E: electric field (V/m); B: magnetic field (T); m/e: mass-to-charge ratio of the particle (kg/C)

Ernest Rutherford

Rutherford fired alpha particles at gold foil and some bounced almost straight back. His formula, with its steep dependence on 1/sin⁴(θ/2), only works if the positive charge sits in a tiny, dense nucleus.

dσ/dΩ = (zZe²/(16πε₀E))² / sin⁴(θ/2)

dσ/dΩ: differential cross section per solid angle (m²/sr); z: charge number of the alpha particle (2); Z: charge number of the target nucleus (gold: 79); e: elementary charge (C); ε₀: vacuum permittivity (F/m); E: kinetic energy of the alpha particle (J)

Splitterra

In April 1932 at the Cavendish Laboratory, John Cockcroft and Ernest Walton fired protons from a high-voltage accelerator at lithium. Scintillation screens flashed with pairs of alpha particles flying apart (Proc. R. Soc. A 137, 229, 1932). It was the first nucleus split by artificially accelerated particles, and the energy released matched E = mc².

p + ⁷Li → 2α + 17.3 MeV

p: proton; ⁷Li: lithium-7 nucleus; α: alpha particle, a helium-4 nucleus

Argonix

Lord Rayleigh weighed nitrogen with great care and found that nitrogen taken from air was about half a percent denser than nitrogen made from ammonia, a gap far larger than his errors. With William Ramsay he removed all the nitrogen and oxygen from air and found a stubborn leftover gas, about 1% of the atmosphere, with a new spectrum and no chemistry at all. They named it argon, ‘the lazy one’ (“Argon, a New Constituent of the Atmosphere”, Phil. Trans. A 186, 187, 1895).

ρ_air N₂ ≈ 1.005 ρ_chem N₂

ρ_air N₂: density of ‘nitrogen’ from air, which still contains argon; ρ_chem N₂: density of nitrogen from chemical sources

Infrara

In 1800 William Herschel placed thermometers in the colours of a prism spectrum and found the temperature rose from violet to red. Then he moved one past the red end, where no light could be seen, and it rose further still (“Experiments on the Refrangibility of the Invisible Rays of the Sun”, Phil. Trans. R. Soc. 90, 284). The Sun emits invisible rays beyond the red: infrared.

λ_IR > λ_red ≈ 0.7 µm

λ_IR: infrared wavelengths, about 0.7 µm to 1 mm; λ_red: long-wavelength end of the visible spectrum

Skyrider

In 1912 Victor Hess carried electroscopes up in balloons to 5 350 m (Phys. Z. 13, 1084). Their discharge rate, a measure of ionising radiation, first dipped slightly, then climbed steeply with height. The radiation was coming from above, not from the ground. A flight during a near-total solar eclipse and at night showed no drop, so the Sun was not the source. He shared the 1936 Nobel Prize for cosmic rays.

ionisation rate rises with altitude

altitude: height above sea level, up to 5 350 m in 1912; ionisation rate: ions formed per cm³ per second in the electroscope

Aberra

From 1725 James Bradley tracked the star Gamma Draconis and found it shifted through the year by about 20 arcseconds, but in a pattern that did not fit parallax. In 1729 he explained it (Phil. Trans. R. Soc. 35, 637): Earth is moving, so the telescope must be tilted slightly forward to catch starlight, like slanting an umbrella when you walk in rain. The tilt is set by Earth’s orbital speed compared with the speed of light.

θ ≈ v/c ≈ 20.5″

θ: aberration angle (rad, here ≈ 20.5 arcseconds); v: Earth’s orbital speed, ≈ 30 km/s; c: speed of light (m/s)

Ole Rømer

Io's eclipses behind Jupiter ran later when Earth was farther from Jupiter, because the light had farther to travel. Rømer used that delay to show that light has a finite speed, crossing the width of Earth's orbit in a matter of minutes.

Δt = Δd/c

Δ t: extra light travel time (s); Δ d: extra distance light must travel (m); c: speed of light in vacuum (m/s); AU: astronomical unit, about the mean Earth–Sun distance (exactly 149 597 870 700 m since 2012) (m)

Homestaka

Raymond Davis Jr.'s experiment in the Homestake gold mine, South Dakota, 1478 m underground, used a tank of about 615 tonnes of perchloroethylene (tetrachloroethylene, C₂Cl₄). A solar electron neutrino can turn a chlorine-37 nucleus into argon-37 (threshold 0.814 MeV), and the few argon atoms were extracted and counted. From 1970 to 1994 it measured about a third of the rate predicted by John Bahcall's standard solar model.

measured 2.56 ± 0.16 ± 0.16 SNU vs predicted 7.6⁺¹·³_−1.1 SNU

SNU: solar neutrino unit: 10⁻³⁶ captures per target atom per second; 2.56: final Homestake result (Cleveland et al., ApJ 496, 505, 1998), statistical and systematic errors; 7.6: chlorine prediction of the BP2000 standard solar model (Bahcall, Pinsonneault and Basu, 2001)

Galileo Galilei

Galileo found that a falling body's distance grows with the square of the time. In equal time intervals the distances covered go in the ratio of the odd numbers 1, 3, 5 and so on, which is the signature of constant acceleration.

d = ½gt²

d: distance fallen from rest (m); g: gravitational acceleration (m/s²); t: time (s); d_n: distance covered in the n-th equal time interval (m)