– • / • – indicates an open/off switch
– • – • – indicates a closed/on switch
If you and another friend create a system where you control a lightbulb in their room via a switch in yours, and vice versa, then you’ve created a bidirectional telegraph system
* consists of two identical circuits that are entirely independent of each other, and unconnected. In theory, messages could be sent and received simultaneously
* you can use a ‘common circuit’ to reduce the length of electrical connections
-> Once you’ve established a common part of a circuit, you don’t have to use wire for it. You can replace wire with something else, like the literal planet Earth.
The Earth is a good conductor because it’s so large, but to use it as such, you need a conductor with a large surface area a.k.a. substance that maintains substantial contact with the earth.
* a copper pipe at least 8’ long and .5” in diameter works
A ground / an earth: an electrical contact with earth / a physical connection with the earth
* but ground can also mean the part of a circuit we’ve been calling the ‘common circuit’
The earth is to electrons as an ocean is to drops of water.
* It’s a virtually limitless source of electrons and also a giant sink for electrons
* but it has some resistance, which is why you need a big enough pole or conductor
V can stand for voltage, but it can also stand for vacuum.
* Think of V as an electron vacuum
* Think of the ground as an ocean of electrons
* The electron vacuum pulls electrons from the earth through the circuit, doing work along the way (lighting a lightbulb)
Ground is sometimes known as point of zero potential -> no voltage is present.
We started with communicating with Morse code but only in a straight line of sight and only as far as the beam from a flashlight could travel.
Now using wires, we’ve constructed a system to communicate beyond the line of sight, and freed ourselves of the limitation of distant by using the earth as a conductor/replacement for part of the wire.