Franklin second to Coulomb per second

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.

In dimensional analysis and physics derivations, C/s makes the relationship between charge and current explicit. When you are computing how much silver an electroplating bath deposits (Faraday's law), writing current as C/s reminds you that charge = current × time, which directly gives the mass deposited.

One coulomb is approximately 6.242 × 10¹⁸ electrons — about 6.2 quintillion. At 1 C/s (1 A), that many electrons pass a point in your wire every single second. A USB cable charging your phone at 2 A carries 12.5 quintillion electrons per second. The numbers are staggering but the charges are tiny.

Not directly — every instrument reads in amperes or milliamperes. But coulomb-counting battery fuel gauges internally track charge in coulombs by integrating current over time: ∫I dt. The C/s framing appears in battery management system firmware and electrochemistry literature where charge balance matters.

Faraday discovered that the mass of metal deposited at an electrode is directly proportional to the total charge passed (in coulombs). For silver, 107.87 grams deposit per 96,485 C (one Faraday). So a 10 A electroplating bath running for 1 hour passes 36,000 C and deposits about 40 g of silver. Thinking in C/s makes the calculation: current × time × atomic weight / (valence × 96,485).

A shunt resistor or Hall sensor continuously measures current flowing in and out of the battery. The BMS integrates this current over time (summing C/s × Δt) to track net charge. Drift and measurement errors accumulate, so smart BMS designs periodically recalibrate against voltage-based state-of-charge estimates.