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Solved exercise · level 4 of 5

Generalised Ohm's law: missing EMF

Skills: Calculate

Statement

Two generators (E₁ unknown and E₂ = 20 V) feed in series three loads with back-EMFs 10 V, 10 V and 9 V. The sum of all circuit resistances (internal and external) is ΣR = 5 Ω and the current is I = 2 A. What is E₁?

E₂ = 20 V · ΣE′ = 29 V · ΣR = 5 Ω · I = 2 A

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

Guided problem in 4 steps: unknown, formula, units, data, result.

1 hint from Bastaya available in the lab
Solution

ΣE = ΣE′ + ΣR · I → E₁ + E₂ = 29 + 5 × 2; E₁ = 29 + 5 × 2 − 20 = 19 V.

Course sheet of the chapter : Real generators & loads

This chapter is covered by the paths: General electricity, Measurement prep, 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.

Shortcuts

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C
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