Electricity
Physics · विद्युत · 24 facts
Electric current: charge flow through conductor; unit=Ampere
Conventional: positive to negative; electron flow opposite
Voltage: work to move unit charge; unit=Volt
Ohm Law: V=IR (constant temperature)
Resistance: opposition to current; unit=Ohm; R=rho.L/A
R increases with length/temperature; decreases with area
Series: same current, R=R1+R2+R3, voltage divides
Parallel: same voltage, 1/R=1/R1+1/R2+1/R3, current divides
Power P=VI=I2R=V2/R; unit=Watt
Heating: H=I2Rt (Joule Law); heater, iron, fuse
Fuse: melts on excess current breaking circuit
Conductors: metals(silver best); Insulators: rubber/wood; Semi: Si,Ge
Superconductor: zero resistance below critical temperature
AC: direction changes; India 220V 50Hz
DC: one direction only; batteries produce DC
Tesla=AC champion; Edison=DC (War of Currents)
Bill in kWh; 1 unit=1000W for 1 hour
Earthing: safety; excess current to earth
Coulomb Law: F=kq1q2/r2; like repel, unlike attract
Cell: chemical to electrical; Battery=group of cells
MCB: modern fuse; can be reset
LED: energy-efficient semiconductor light
Kirchhoff: current in=out at junction; voltage sum in loop=0
Household parallel wiring: each appliance gets full voltage