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Solved exercise · level 4 of 5

Efficiency of a motor

Skills: Measure, Calculate

Statement

Motor M1 has an armature resistance r' = 1 Ω. V1 measures its voltage, A1 its current.

Absorbed power = U × I; Joule losses = r' × I²; mechanical power = absorbed − losses. Compute the motor efficiency.

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

3 hints from Bastaya available in the lab
Solution

Pa = U·I = 12 × 4.8 W; losses = 1 × 4.8² W; Pmech = E'·I with E' = U − r'·I = 7.2 V; η = E' / U = 0.6.

Course sheet of the chapter : Power, energy, efficiency

This chapter is covered by the paths: General electricity, 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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R
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C
chip brush
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