Perrin Brownian Motion
Jean Perrin's 1908 experiment — direct evidence for atomic theory
Parameters
Temperature (K)
300
Viscosity (mPa·s)
1.0
Particle radius (nm)
500
Time step (ms)
50
Particles
8
Reset Trajectories
Pause
Einstein-Smoluchowski relation:
D = k_B T / (6πηr)
Mean squared displacement:
⟨r²⟩ = 4Dt (2D)
Perrin used this to measure Avogadro's number N_A = RT/D·(6πηr) — confirming atoms exist.
Current D:
—
nm²/ms
Steps:
0
⟨r²⟩ slope:
—
nm²/step