Electrons in a copper wire creep along at a fraction of a millimetre per second, yet the lamp lights the instant the switch closes, because what races along at nearly the speed of light is the electric field, not the particles themselves. Current obeys I = V/R exactly, so one more notch of resistance drops it straight away, dragging the power P = VI and the bulb’s brightness down with it. A short circuit is the extreme case of that same formula: a wire bypassing the bulb makes the resistance all but vanish, the current surges until the fuse melts through, and the circuit only closes again once a fresh fuse is in place.
Electrons in a copper wire creep along at a fraction of a millimetre per second, yet the lamp lights the instant the switch closes, because what races along at nearly the speed of light is the electric field, not the particles themselves. Current obeys I = V/R exactly, so one more notch of resistance drops it straight away, dragging the power P = VI and the bulb’s brightness down with it. A short circuit is the extreme case of that same formula: a wire bypassing the bulb makes the resistance all but vanish, the current surges until the fuse melts through, and the circuit only closes again once a fresh fuse is in place.
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