Litmux Studio

LabWhat electricity is · 15 min

Lab: your first circuit

A 12 V battery, a switch and a 12 V 5 W lamp. You will switch it on, measure the voltage across the lamp with the multimeter, and then find something surprising: where the battery's voltage goes when the switch is open.

The circuit for: Lab: your first circuit
The circuit you start with

The steps

  1. Press RUN. The switch S1 is open, so the loop is broken: the lamp stays dark.RUN is on the toolbar (F5).
  2. Click the switch S1 to close it. The loop is complete and the lamp lights.While the circuit runs, a click on a switch flips it.
  3. Measure the voltage across the lamp. Place the Multimeter (M) and leave it on V⎓. Wire its VΩ socket (red lead) to the lamp's top end and its COM socket (black lead) to the lamp's bottom end. It reads almost 12 V: the lamp gets the whole battery voltage.A voltmeter goes ACROSS a part - one lead on each end. Nothing has to be disconnected.
  4. Click S1 again to open it. The lamp goes out and the meter drops to 0 V: with no current, there is no voltage across the lamp.No current through the lamp means no energy handed over in it - and no voltage across it.
  5. Now move the leads across the open switch: delete the two lead wires (click each, Del), then wire red to S1's left end and black to its right end. The meter reads the full 12 V - the whole battery voltage appears across the gap.Across an open switch you measure the push that is waiting to drive current through it.

What it shows