Tricky Circuit

R1 + R2

One path, two resistors

Share 5 V between two resistors. See why the same current passes through both.

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R1 + R2 · Series circuit
Series circuit. Series means one unbranched current path. R1 and R2 add together; neither resistor uses up current.
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EXPERIMENT BENCH

Change the circuit settings, predict the readings, then check a challenge. These are learning models, with the assumptions explained in each lesson.

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One path, two resistors

Ideal resistors and wires; heating and tolerances are not simulated.

I = 5 / (R1 + R2). The larger resistor gets more voltage. Swapping their order does not change total current. V(R2) is the voltage across R2.

Difficulty

  1. Build · One path, two resistors

    Power on with R1 = R2 = 1000 Ω. Observe 2.50 mA.

    Need a hint?

    R1 = 1000 Ω; R2 = 1000 Ω

  2. Explore · One path, two resistors

    Keep R1 = 1000 Ω; set R2 = 2000 Ω. Compare current and voltage.

    Need a hint?

    R1 = 1000 Ω; R2 = 2000 Ω

  3. Solve it · One path, two resistors

    Choose resistors that produce 1.00 mA at 5 V.

    Need a hint?

    R1 = 2000 Ω; R2 = 3000 Ω

Extra reading and circuit recipes

One path, two resistors

Current is not used up

In this unbranched path, the same steady current passes through both resistors. They convert electrical energy into heat; they do not consume the current. Their voltage drops add to the 5 V supply.

Same current, different heating

Power means energy transferred each second. At the same current, the larger resistor dissipates more power: P = I²R, where I is current and R is resistance. Real resistors have a watt rating; watt is the unit of power. Heating is not simulated here.

At 5 V with R1 = 1000 Ω and R2 = 2000 Ω, which resistor has the larger voltage drop?

  1. R1
  2. R2
  3. Both have the same drop
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R2 has twice the resistance and the same current, so its voltage drop is twice as large: about 3.33 V across R2 and 1.67 V across R1.

Swap without changing the total

Power on. Set R1 = 500 Ω and R2 = 1500 Ω, then swap the values. Predict the current before looking: it stays 2.50 mA. The voltage across R2 changes from 3.75 V to 1.25 V.