1 Base Grid (11” x 7.7”) # 6SC BG
1 Battery Holder (2-AA) # 6SC B1
1 100 ohm Resistor # 6SC R1
1 Slide Switch # 6SC S1
1 Red LED # 6SC D1
For an introduction to the diode, please see my Instructable: http://www.instructables.com/id/Introduction-to-the-Diode-Using-Snap-Circuits/
The Light Emitting Diode functions the same as a diode, but also lights up when enough current is flowing through it in the forward direction (forward-biased). LEDs are often used in electronic devices to indicate that the device is switched on, but can serve many practical purposes.
Build the circuit shown in pictures 2 and 3. When you switch the circuit on...nothing happens. When a circuit is connected to your battery you can think of it as electrons flowing from the positive side of the battery (marked with a "+" sign) to ground (marked with a "-" sign). So, when you switch the circuit on, why doesn't the light LED light up? Because the LED is reversed and blocking the flow of electrcity.
Switch the circuit off and turn the LED around as demonstrated in picture 4. Now you can switch the circuit on and with the LED in the forward-biased direction, it lights up.
Picture 5 is the electronic symbol for the LED so that you will be able to recognize it on an electronic schematic.