Labo Élec

electrical lab simulator
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Exercise from the chapter "Ohm's law & resistance"

Sizing a line

Level 4 of 5 · Skills: Build, Calculate

Statement

Lamp L1 (40 W / 12 V) is supplied through a copper line of 20 m (there and back = 40 m, wire F1). With the current cross-section it gets too little voltage.

Choose for F1 the smallest cross-section among 0.5 · 0.75 · 1 · 1.5 · 2.5 · 4 · 6 · 10 mm² that gives L1 at least 11.4 V (95 % of U).

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

2 hints from Bastaya available in the lab
Solution

R_lamp = 3.6 Ω; to keep 95 % of U, R_line ≤ 189 mΩ; S ≥ 0.017 × 40 / 0.189 ≈ 3.6 mm², hence 4 mm². V1 then reads 11.5 V.

Course sheet of the chapter : Ohm's law & resistance

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-

Workbench

Circuit diagram CEI 60617

How does it work?

The perfboard: each big hole is a circuit node. You push a single leg of a component (resistor, lamp...) into it. The 4 small holes around it are connected to it: that is where chips and leads plug in.

  1. Drag a component onto the board: it snaps onto the grid. R rotates it.
  2. To join neighbouring big holes, click Jumper chip in the palette (or C) then drag on the board: a line of chips is laid at once. Bridged holes become a single node.
  3. For long links and for the power supply (placed next to the board), drag a lead from one big hole to another (or to a terminal).
  4. As soon as a loop is closed, the circuit is solved in real time (Ohm + Kirchhoff) and the diagram follows.
  5. Zoom with the wheel (or + / −, two-finger pinch); drag the background to pan, 0 fits the board. The + buttons around the board add a row or a column.

Del delete · R rotate · C chip brush · Esc cancel · wheel zoom · drag the background to pan

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