Series and parallel circuits

Equipment

• Two-resistor circuit model with the «Switch to parallel» button
• Source-voltage, R₁, and R₂ sliders
• Virtual ammeter/voltmeter and branch readouts

Procedure

1. Explore the series circuit

   Set U = 9 V, R₁ = 3 Ω, R₂ = 6 Ω. Read the current through each resistor — identical, $I=U/(R_1+R_2)=0.6$ A — and the voltage across each: $U_1=1.8$ V, $U_2=3.6$ V, summing to 9 V (Kirchhoff's loop rule).

2. Switch to parallel

   Press «Switch to parallel», keeping U, R₁, R₂. Both branches see the same 9 V; read branch currents $I_1=U/R_1=3$ A, $I_2=1.5$ A; the total $I=I_1+I_2=4.5$ A (Kirchhoff's junction rule). Equivalent resistance $R_p=U/I=2$ Ω — matching $1/R_p=1/3+1/6$.

3. Compare power and brightness

   In panel 2, watch the charge carriers in the branches and compare their «crowding» — a picture of current. Compute $P=UI$ for each configuration: parallel dissipates much more power than series because $R_p<R_s$ — which is why home lamps are wired in parallel.

4. Predict with chosen values

   Pick any U, R₁, R₂; compute $I_s=U/(R_1+R_2)$ and $I_p=U/R_1+U/R_2$ beforehand, then toggle the mode to check. Try the limit R₂ → 1 Ω in parallel: that branch «dominates» the current — the small resistor rules in parallel, the large one in series.

Simulation

Experiment history

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