Franklin second to Biot

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 CGS-EMU system defines its base units using centimeters, grams, and seconds instead of meters, kilograms, and seconds. The factor of 10 falls out naturally from the dimensional conversion: 1 Bi produces 2 dyn/cm force between wires 1 cm apart, and working through the CGS-to-SI conversion yields exactly 10 A.

Biot was a French physicist (1774–1862) who co-discovered the Biot–Savart law in 1820, describing how electric current generates a magnetic field in space. This was one of the foundational results linking electricity to magnetism. The CGS community honored him by naming their electromagnetic current unit after him.

Essentially no. Even theorists who prefer CGS units typically use Gaussian units rather than pure CGS-EMU. The biot appears mainly in textbook conversion tables, historical physics papers, and graduate-level electrodynamics courses that teach multiple unit systems for pedagogical reasons.

Multiply biots by 10 to get amperes; divide amperes by 10 to get biots. A 30 A circuit carries 3 Bi; a 0.5 Bi current is 5 A. It is one of the simplest unit conversions in physics — just move the decimal point one place.

The Biot-Savart law calculates the magnetic field produced by a small segment of current-carrying wire at any point in space. In CGS-EMU, it uses biots for current and gauss for the field. In SI it uses amperes and teslas. The law itself is fundamental — it is used to design MRI magnets, motors, and particle accelerators.