A two-bulb desk fixture is wired in parallel. One bulb burns out. Does the other go dark, go dim, or carry on?
You know what a break does to a series circuit. Check it first:
A series loop holds a buzzer and a bulb. The bulb's filament snaps. What does the buzzer do?
In a series loop, one break stops everything. A parallel circuit answers the question differently.
Here are the fixture's two lamps before the break. Each branch carries its own current, and each branch has the full source voltage.
Lamp L1 burns out. Its filament breaks, so its branch is no longer a complete loop. The current in that branch stops.
Lamp L2's branch is untouched. It still runs from one battery terminal to the other: a complete loop on its own. So L2 still has the full source voltage across it. The same voltage across the same lamp drives the same current. The same current through the same lamp gives the same brightness. L2 carries on exactly as before.
Here is the charge-stream visualization from earlier in this topic again. Watch the parallel half: each branch carries its own stream, with the full source voltage across it.
One of two parallel lamps burns out. What does the other lamp do?
A buzzer and a pump share a parallel supply. The pump breaks, and the buzzer sounds unchanged. Why?
The battery does feel the change. It now supplies only L2's branch. The supply current falls by the amount the broken branch used to carry.
One branch of a parallel pair breaks. What happens to the current supplied by the battery?
A buzzer and a motor share a parallel supply. The motor's winding breaks. What happens to the buzzer?
The buzzer's branch is still a complete loop with the full source voltage across it.
The same voltage across the same buzzer drives the same current.
The buzzer sounds on, unchanged.
Before the break, the motor's branch carried 0.7 A and the buzzer's branch 0.3 A. What is the supply current after the break?
Only the buzzer's branch still carries current.
The supply current is now the buzzer's branch current alone: 0.3 A.
The supply current falls from 1.0 A to 0.3 A.
Compare the two circuit types. In a series circuit, one break stops the current everywhere. In a parallel circuit, a break stops the current in that branch only.
Lamp pair S is wired in series; lamp pair P is wired in parallel. One lamp in each pair burns out. What happens?
A barn fan and its light run on parallel branches. The fan's motor burns out. What does the light do?
After one of two parallel lamps fails, a student expects the survivor to brighten. What actually sets the survivor's brightness?