Ohm's lawlaw
Georg Ohm in 1826 experimentally investigated how metals conduct electricity. At that time, it was believed that current is a flow of a mysterious fluid. Ohm established a clear mathematical relationship: current I = U / R, where R is a characteristic of the conductor. He presented the result in the book 'The Galvanic Circuit Investigated Mathematically', but colleagues received the work coldly. Recognition came only a few years later. Today Ohm's law is the ABC of electrical engineering: in any microchip, transformer, LED strip, it is essential.
How it works
In a hair dryer, the heating coil has high resistance: current heats it, delivering power. The diameter of power line cables is huge to reduce resistance and energy loss to heat. In wet weather, insulation deteriorates, resistance drops, current increases — because of this, the RCD trips.
💡 The human body is a conductor. The resistance of dry skin is ~100 kΩ, while wet skin drops to 1 kΩ. The danger of electric shock increases dramatically after a shower.
I = \frac{U}{R}
I is current (amperes, A), the amount of electric charge passing through the cross-section of a conductor per unit time; U is voltage (volts, V), the potential difference across the conductor; R is electrical resistance (ohms, Ω), a measure of the conductor's opposition to current.
\mathbf{j} = \sigma \mathbf{E}
j is current density vector (A/m²), current per unit cross-sectional area; σ is specific electrical conductivity (S/m), the reciprocal of resistivity ρ (σ = 1/ρ); E is electric field strength vector (V/m).