Labo Élec

electrical lab simulator
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Exercise from the chapter "Measurement & instruments"

Not-so-perfect voltmeter

Level 4 of 5 · Skills: Analyse

Statement

R1 = 22 kΩ and R2 = 10 kΩ in series at 12 V. Voltmeter V1 across R2 has an internal resistance of only 100 kΩ (adjustable in the inspector).

What voltage does it display? (It disturbs the circuit: R_V is in parallel with R2.)

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

2 hints from Bastaya available in the lab
Solution

R2 ∥ R_V = 10000 × 100000 / (10000 + 100000); U_meas = 12 × R2' / (R1 + R2') = 3.51 V. With a 1 GΩ voltmeter you would read 12 × R2 / (R1 + R2).

Course sheet of the chapter : Measurement & instruments

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

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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