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Solved exercise · level 4 of 5

Find R₁ thanks to the wattmeter

Skills: Measure, Calculate

Statement

R₁ (unknown), R₂ = 10 Ω and R₃ = 82 Ω are in series at 12.1 V. Wattmeter W1 measures the power absorbed by R₂.

Deduce the value of R₁.

Parametric exercise: the values change with every draw; these are one example.

3 hints from Bastaya available in the lab
Solution

W1 reads P₂ = 25 mW; I = √(P₂ / R₂) = 0.05 A; Req = U / I = 12.1 / 0.05 Ω; R₁ = Req − 10 − 82 = 150 Ω.

Course sheet of the chapter : Resistor networks

This chapter is covered by the paths: ISL-oriented exercises

Other exercises of the chapter

Simulated time00:00:00
Q = I·t-
W = P·t-

Circuit diagram CEI 60617

How does it work?

Each big hole is a circuit node: you push one leg of a component into it. The 4 small holes around it are connected to it: chips and leads plug in there.

  1. Place a component Drag it from the palette: it snaps onto the grid. R rotates it.
  2. Bridge neighbouring holes Pick the jumper chip (or C) and drag on the board: bridged holes become a single node.
  3. Draw a lead For long links and the power supply: from one big hole to another, or to a terminal.
  4. Close the loop The circuit is solved live (Ohm, Kirchhoff) and the diagram follows.

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