Franklin second to CGS e.s. unit

Franklin (1706–1790) was the American polymath who proved lightning is electrical with his famous kite experiment in 1752. He introduced the convention of "positive" and "negative" charge that we still use today. He arbitrarily assigned positive to the charge on glass rubbed with silk — which turned out to be a deficit of electrons, giving us the unfortunate convention that current flows opposite to electron motion.

The roentgen (R) was defined in 1928 as the radiation exposure producing 1 ESU of charge (1 franklin ≈ 3.336 × 10⁻¹⁰ C) per cm³ of dry air at STP. This CGS-era definition stuck because radiation safety regulations were already built around it. Even though the SI gray replaced the roentgen for dosimetry, the roentgen — and its franklin-based definition — persists in US regulatory and medical imaging contexts.

The legacy unit of radiation exposure, the roentgen (R), is defined as the amount of X-ray or gamma radiation that produces 1 esu of charge (1 franklin) per cubic centimeter of dry air at STP. This definition dates from the 1920s when CGS-ESU was standard. Modern dosimetry uses grays and sieverts, but the roentgen and its franklin-based definition persist in some medical and regulatory contexts.

One Fr/s is about 0.33 nanoamperes — less current than a sleeping microcontroller draws. To equal the 1 A flowing through a phone charger cable, you would need about 3 billion franklins per second. The unit is spectacularly impractical for anything beyond electrostatics calculations.

Sort of. He labelled the charge on glass rubbed with silk as "positive," not knowing it was caused by removing electrons. When Thomson discovered the electron in 1897, it turned out electrons carry what Franklin called negative charge. So conventional current flows from + to −, opposite to actual electron flow. Engineers and physicists have lived with this "mistake" for over 250 years.

The e.m. unit equals 10 A while the e.s. unit equals 3.3 × 10⁻¹⁰ A — a ratio of about 3 × 10¹⁰, which is the speed of light in cm/s. This enormous factor reflects the fundamental relationship c² = 1/(ε₀μ₀). The two systems were designed to simplify different sets of equations, and the speed of light is the price of bridging them.

In vacuum tubes and cathode ray experiments, electrostatic forces dominate — no magnetic materials, no currents in bulk conductors. The ESU system made Coulomb's law beautifully simple: F = q₁q₂/r² with no constants. For computing electron trajectories in early TV tubes and oscilloscopes, this simplicity was genuinely helpful.

Early cathode ray tubes used electrostatic deflection plates to steer the electron beam. Engineers working in CGS-ESU could calculate beam deflection angles directly from plate voltage and geometry using Coulomb's law without extra constants. The tiny ESU currents matched the actual beam currents (microamperes), making the numbers more intuitive than working in amperes for these minuscule electron flows.

Check the context and the magnitude of numbers. If currents are tiny numbers where you would expect amperes, it is ESU. If they are 1/10 of expected ampere values, it is EMU. Good papers state which system they use, but many older ones do not. The equations themselves also differ — look for factors of c or 4π.

Technically yes, but clumsily. In pure CGS-ESU, the magnetic field has dimensions involving the speed of light, and equations for inductance and magnetic force become awkward. This is exactly why the Gaussian hybrid was invented — it uses ESU for electric quantities and EMU for magnetic ones, giving clean equations for both.