Weber per henry to Franklin second

When designing a transformer, you start with the required flux (webers) to transfer power at a given voltage and frequency. The core's inductance (henries) is set by geometry and material. Dividing flux by inductance gives the magnetising current that must flow — and if it is too high, the core saturates and the transformer overheats.

One weber is the magnetic flux that, when reduced to zero in one second, induces one volt in a single-turn coil. A small transformer core might carry 0.001 Wb (1 mWb) of peak flux. The Earth's magnetic field through a 1 m² loop is about 50 μWb. One weber is actually an enormous amount of flux in everyday terms.

If the calculated magnetising current (Wb/H) exceeds design limits, the core is approaching magnetic saturation. The inductance drops sharply, current spikes further, and the inductor or transformer overheats. Solutions include using a larger core, higher-permeability material, an air gap, or reducing the operating flux density.

Every magnetic core has a saturation flux density (e.g., 1.5 T for silicon steel, 0.3 T for ferrite). When flux approaches this limit, permeability collapses, inductance plummets, and Wb/H (current) shoots up. Power supply designers must ensure peak flux stays 20–30% below saturation under worst-case conditions.

An air gap dramatically increases the reluctance of the magnetic circuit, which lowers inductance (H) for the same core geometry. For a given flux (Wb), the magnetising current (Wb/H) increases — but the core is far harder to saturate. Power supply designers deliberately add 0.1–1 mm air gaps to ferrite cores so the inductor can handle higher peak currents without the flux density hitting saturation limits.

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.