Electricity

Flow of electric charge. I = Q/t. Unit: Ampere (A). 1 A = 1 coulomb per second. Current flows from higher potential (+) to lower potential (-). Conventional current: positive to negative. Actual electron flow: negative to positive (opposite direction).

Work done per unit charge: V = W/Q. Unit: Volt (V). 1 V = 1 Joule per Coulomb. Measured by voltmeter (connected in parallel). EMF = energy provided by battery per unit charge. Potential difference drives current.

V = IR (at constant temperature). Resistance R = V/I. Unit: Ohm (Ω). 1 Ω = 1 V/A. Ohmic conductors: V-I graph is straight line. R = ρL/A (resistivity × length / area). Resistivity depends on material and temperature. Metals: resistance increases with temperature.

Series: same current through all. Voltages add up. R_total = R₁+R₂+R₃. If one bulb fails, ALL go off. Parallel: same voltage across all. Currents add up. 1/R_total = 1/R₁+1/R₂. If one fails, others continue. Home wiring = parallel.