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Solved exercise · level 3 of 5

Lamp at another voltage

Skills: Analyse

Statement

Lamp L1, rated 100 W / 24 V, is supplied at 12 V. Its resistance is assumed constant.

What power does wattmeter W1 (display hidden) show?

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

3 hints from Bastaya available in the lab
Solution

The resistance R = 24² / 100 does not change; P = U² / R = 0.5² × 100 = 0.25 × 100 = 25 W: the power varies as the square of the voltage.

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.

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