Mercury at 4.2 K

Plate 61 speaks for itself: “Cold mercury: resistance drops to zero.”

The Physics

Kamerlingh Onnes cooled mercury with liquid helium in 1911 and saw its resistance vanish abruptly near 4.2 K: the discovery of superconductivity.

R(T < T_c) = 0

• R: electrical resistance, Ω
• T: temperature, K
• T_c: critical temperature, ≈ 4.15 K for mercury

Mercury, cooled by liquid helium. Near 4.2 K, R became unmeasurable.

Honest caveat: 'Zero' means below any measurable value; persistent-current experiments later bound it far below normal resistance.

Sources

• H. Kamerlingh Onnes, Commun. Phys. Lab. Univ. Leiden 120b (1911).

On the poster

Plate 061, “Mercury at 4.2 K”: the pixel-art plate with its slogan “Cold mercury: resistance drops to zero.”, the key equation and the facts panel shown above. Pixelated Physics. Physics. Personified.