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Experiment 19 - The Internal Resistance of the Capacitor

Capacitors have a very low internal resistance. You can illustrate this with the circuit shown...

Circuit internal resistance of a capacitor. (Enlarge)

Circuit diagram internal resistance of a capacitor.


Capacitors are used wherever you need very short high current pulses, eg in spot welding or in the generation of high magnetic fields.

View circuit internal resistance of a capacitor. (Enlarge)

By pressing the pushbutton switch S1 you charge the two capacitors C1 and C2.

In a second step, you bring the two tips of the loose wires in contact. This shorts the capacitors and you watch two things...

  • a small flash at the moment of short circuit,
  • whereupon the two tips "stick" together....

The high short-circuit current welded the tips together...

You can never obtain the same result with a 9 Volt Block Battery. The higher internal resistance prevents this.