CHAPTER 11 ■ POWER ON!
Do You See The Light?
Hopefully you’re patting yourself on the back for a job well done. You’ve got a beautiful red light.
If the red LED isn’t lit, check all of your connections. Alligator clips tend to slip off.
If the red LED still isn’t lit, perhaps it’s in backwards. No harm done. Disconnect both ends of the LED,
flip it around, and reconnect both ends.
Experimenting with the Power Indicator Circuit
After admiring your red LED for a while, here are some things to try:
- Disconnect the red LED and put a different color or size in its place.
- Reverse the resistor connections. It won’t make any difference; the resistance
won’t change. Resistors are non-polarized. That is, resistors don’t care which end
is connected to the negative or the positive. This is a fairly boring experiment since
nothing happens differently when the resistor is flipped, but that alone is worth
noting. - Reverse the LED connections. It won’t light in the wrong direction. LEDs are
polarized. That is, they do care which end is connected to the negative and the
positive. - Disconnect any one of the alligator clips. The LED turns off. It doesn’t matter where
you disconnect a circuit; if the entire branch or loop isn’t connected to both ends of
the battery, it stops working. (Because the pipe cuts off before reaching the other end
of the battery, there isn’t anywhere for the electrical drops to go. With nowhere to
go, there isn’t any room for more drops to get squeezed out. It’s a bad traffic jam on a
dead-end street.)
Understanding the Roles of Each Component
Each part of the power indicator circuit provides a vital function.
The battery, B1, is the pump. It takes electrons (electricity drops) and sends them around and around
the loop.
The alligator clips and wire leads are the pipes. They deliver the electrons to the desired parts.
The resistor, R1, protects the “delicate” LED from the full force of the battery. Recall that resistors are
like narrower pipes or skinny holes that only let a desired maximum amount of electricity through.
The resistor’s restriction of flow also prevents waste. We only care that the LED lights up, we don’t want
to use any more battery power than that.
The red LED, D1, is the purpose of the circuit. The battery, wires, and resistor are only there to provide
for the LED’s needs.
Measuring the Power Indicator Circuit
Within a circuit, there are two useful measurements that you can make: voltage (pressure) and current (flow).