Cube3D 立方体数理Physics · Middle school / High school
One bulb is removed: series or parallel circuits?
Two bulbs can look similar on a table yet behave differently when one is removed. The important clue is the route available to current. In a series circuit there is a single continuous path. In parallel, separate branches provide separate paths between the supply terminals.
Predict before you open a branch
In the free circuit lab, choose series, keep both bulbs connected and close the main switch. Predict whether bulb 2 will remain lit if bulb 1 is removed. Then remove bulb 1. The single route is broken, so current stops throughout the circuit.
Reconnect the bulb, choose parallel and close the switches. Remove bulb 1 again. Its branch is now open, but bulb 2 still has a complete route through the supply. In this ideal model, its voltage and resistance remain unchanged, so its current and power remain unchanged too.
Use numbers to explain the difference
Set an ideal supply of 6 V and two 10 Ω bulbs. In series, the total resistance is 20 Ω, so the current is 6 ÷ 20 = 0.30 A through both bulbs. Each has a 3 V potential difference and dissipates 0.90 W.
In parallel, each 10 Ω bulb is connected across 6 V. Each branch carries 0.60 A and dissipates 3.60 W. The supply current is the sum, 1.20 A. These figures explain why comparing brightness requires specifying both the connection and the supply.
Check your understanding
If one of the two equal parallel branches is opened, what happens to the supply current and the current in the remaining branch? State the assumption about the supply.
Show the explanation
With an ideal constant-voltage supply, the remaining branch current is unchanged and the supply current halves. A real supply with internal resistance can behave differently.
What the model assumes
The simulation treats bulbs as fixed resistors and uses electrical power to indicate brightness. Real filament resistance changes with temperature. This browser task is not an instruction to experiment with household mains electricity.