Resistance
Definition
How much a material opposes the flow of electric current — the electrical equivalent of friction.
Symbol: · Unit: ohm (Ω)
Technical definition
The ratio of voltage to current, R = V/I, measured in ohms. It arises from collisions between charge carriers and the material's atomic lattice, converting electrical energy into heat.
Example
A 60 W incandescent bulb has a hot resistance of about 240 Ω — high enough to make the filament glow white-hot. That 'waste' heat is exactly how the bulb makes light.
Resistance does not 'use up' current. In a series circuit the same current flows through every resistor — what each resistor consumes is energy (the voltage drops across it), not charge. Students who think current gets 'used up' by resistors cannot explain why the current is identical on both sides of a bulb.