Use Kirchoff’s Current Law

Let’s test Kirchhoff’s current law by verifying the current into a node is equal to the sum flowing out.  We can do this by connecting another green LED circuit to the ammeter. 

Both LED circuits will conduct about 5 mA.  If both of them are connected to ground through the ammeter, the sum of the currents flowing through the 20 Ω resistor should be about 10 mA.

• If the 1 kΩ resistor is still in the LED circuit, remove it and replace it with the 220 Ω resistor (color code red-red-brown-gold).
• Make sure the measurement is in the 5 mA neighborhood.
• Click the CYBERscope’s Disconnect button.
• Disconnect the USB cable.
• Build a second green LED circuit with a  220 Ω resistor, and verify that it emits light when connected to GND.

• Disconnect the second LED circuit from GND, and plug it into the same row as the red ammeter probe.
• Click the CYBERscope’s Connect button, and verify that the current through the ammeter has approximately doubled.