How does the LED work?
One prong is longer than the other, and there is a certain way to place it in the breadboard. If you don't put it in correctly it will destroy the LED light.
How Buzzer Circuit Works
The top bus connects to one of the long white wires. The other white wire is connected to E15 and when they connect they complete the circuit. And how do they connect the circuit? It's because of the short blue wire that's connected to E9. That connects to a resistor on the bottom terminal strip that connects to the bottom bus connecting to the black wire.
How Pot In LED Works
If the left and middle Pot wires are connected, turning the Pot knob to the right makes the LED dimmer, because the electricity has to travel a farther distance through the resistant wire. If we hook up the wires to the middle and right of the Pot, turning the knob Pot clockwise will get brighter, for the same reason as when we hooked it up the previous way.
How does the addition of the NPN transistor work?
By using the transistor controlled by the phototransistor to complete the LED circuit to the battery, it allows more current flow to the LED than using the phototransistor in line by itself. This is because the current through the phototransistor is limited by how much infrared light is emitted by the infrared LED.
Capacitor leaks current as it charges
The light goes out because when the capacitor is full, then current cannot flow through it so no current goes to the LED.
About the NPN Transistor
If the flat side is facing you then the left prong of the NPN transistor emits electricity. If the middle or base prong is powered it can turn on lights, make buzzers buzz, and any other things that are connected to the left prong. And the right prong is the collector.