4.1 (An Introduction to Electricity Via Electrical Circuits)

-> Electricity is an amazing phenomenon that is pervasively useful and yet remains mostly mysterious – even to those who pretend to know how it works.

The Components of a Flashlight (An Electrical Appliance)

Disassembled, a common household flashlight includes:

1. A few batteries

2. A bulb

3. A switch

4. Some metal pieces

5. Some short pieces of insulated wire

   1. with the insulation stripped from the ends

6. A plastic case to hold everything together

A Simple Electrical Circuit

-> You can make an electrical circuit (bare-bones flashlight) by using only components 1, 2, and 5 from the household flashlight.

• A circuit is a circle

  • Lightbulb will only be lit if the path from the batteries to the wire to the bulb to the switch and back to the batteries is continuous (switch = break in wires)

    • Purpose of the switch is to control this process

A ‘water and pipes’ analogy is common when describing how electricity works, but it doesn’t really describe electricity at all. Electricity has to be described on its own terms.

4.2 (Electron Theory)

-> Says that electricity derives from the movement of electrons

Atoms

• All matter is composed of extremely small things called atoms

• Atoms are composed of three types of particles:

  1. Neutrons

  2. Protons

  3. Electrons

• An atom is like a little solar system, with neutrons and protons bound into a nucleus, and electrons spinning around the nucleus like a heliocentric model

  • This isn’t exactly what you’d see IRL, but it’s a convenient model

So you determine which of 112 elements you want by paying attention to the number of electrons, protons, and neutrons an atom/element has

Atomic Number: Indicates the number of protons in the nucleus of each of the element’s atoms, and also usually the number of electrons in each atom.

Molecules

Molecule: Formed out of atoms that have chemically combined with other atoms.
* Molecules have very different properties than the atoms of elements that they’re made of
* A water molecule is very different than its two atoms of hydrogen or single atom of oxygen observed on their own
* A molecule of table salt is very different than its one atom of chlorine and one atom of sodium observed on their own

The Components of Matter

Elements:
* hydrogen
* oxygen
* sodium
* chlorine

Compounds:
* water
* salt
* the two components don’t maintain their own properties

Mixtures:
* saltwater
* the two components maintain their own properties

4.3 (How Electricity Happens)

-> The number of electrons and protons in an atom (the atomic number) is usually the same.

Electricity happens when the electrons are dislodged from atoms.

Etymology of ‘Electricity’

‘Electron’ and ‘electricity’ derive from Ancient Greek word ‘elektron’
* it’s the greek word for ‘amber’ (the glasslike hardened sap of trees)
* ancient Greeks experimented with rubbing amber with wool to produce static electricity by causing the wool to pick up electrons from the amber.
* the wool ended up with more electrons than protons, and vice versa with the amber.
* a modern example is carpeting picking up electrons from the soles of our shoes

Charge

-> Protons and electrons have a charge – positive and negative, respectively
* but this designation (+ and -) is just meant to show that they’re opposite in how they relate to each other

Ways to Describe the Relationship Between Protons and Electrons

1. The circuitous route of electricity from the carpet through your body and back to your shoes

   1. Equal numbers of electrons and protons = stability

   2. Imbalance of electrons and protons = attempts to correct itself

2. Opposite charges attract and like charges repel

   1. Protons are held together by strong force which overcomes the repulsion of their like charges in the nucleus

The Strong Force

-> Experimenting with strong force involves splitting apart the nucleus, which produces nuclear energy
-> But right now we only want to experiment with electrons to produce electricity

Static electricity is also at play when clouds accumulate electrons at their bottoms while losing them at their tops – the imbalance is resolved via a bolt of lightning

Lightning: a lot of electrons moving very quickly from one spot to another

How Electricity in a Circuit Works

1. Electricity in a circuit = the passage of electrons from atom to atom

2. We need something to precipitate the movement of electrons around the circuit

   1. In the case of the barebones flashlight, that’s the batteries

Anatomy of a Battery

• Flat end of battery = minus / negative side = negative terminal / anode

• End with a protrusion = plus / positive = positive terminal / cathode

• Chemical reactions take place in all batteries

Chemical reaction: When some molecules break down into other molecules, or when molecules combine to form new molecules.

Within batteries, chemical energy is converted to electrical energy.

• The reactions only take place when an electrical circuit is present to take electrons away from the anode and supply them via the cathode in a counterclockwise direction.

All electrons are always identical.

• there’s nothing that distinguishes an electron from one element from an electron of another.

Combining batteries increases their voltage.

• batteries can be connected in parallel or in series

Different Perspectives

1. A battery provides electricity to a circuit

2. A circuit provides a way for a battery’s chemical reactions to take place

Electricity can flow through air -> lightning

• it’s easier when the air is wet/humid

• but it doesn’t usually flow readily

Conduction

Some substances do carry electricity better than others

Conduction: The ability of an element to carry electricity, which is related to its subatomic structure
* almost anything will conduct electricity if the voltage is high enough

Atoms have shells a.k.a. the various levels at which electrons orbit the nucleus

Conductor: A substance that is conducive to carrying electricity, especially copper, silver, and gold.
* the atoms in these elements have just one electron in their outer shells that can be readily given up

Resistance is the opposite of conduce. Similar to the width of a pipe in plumbing – smaller pipe = more resistance

Resistor: A substance with more resistance to the passage of electricity than others.

Insulator: A substance that has resistance so high that it doesn’t conduct much electricity at all. (e.g.rubber and plastic)

4.4 (Voltage)

-> A difficult concept in elementary electricity

Named after Count Alessandro Volta who invented the first battery in 1800.

Voltage: Refers to a potential for doing work. It exists whether or not something is hooked up to a battery.

Ampere

-> Ampere = amp

• To get one amp of current, you need 6,240,000,000,000,000,000 electrons flowing past a particular point per second

Named after André Marie Ampére of the 19th century

Current: Related to the number of electrons actually zipping around the circuit. Measured in amperes. Similar to water pressure.

Back to the Water and Pipes Analogy

Current -> amount of water
Voltage -> water pressure
Resistance -> width of pipe

The amount of water flowing through a pipe (current) is directly proportional to the water pressure (voltage) and inversely proportional to the skinniness of the pipe (resistance).

Resistance: the tendency of a substance to impede the flow of electrons. It’s measured on ohms

Ohm’s Law

-> Ohms are named after Georg Simon Ohm who proposed this law. The law states:

If:
I = Current (in amperes)
E = Voltage (electromotive force)
R= Reisitance

Then:
I = E / R

A squiggly line in an electrical diagram = symbol for a resistor

How Lightbulbs Work

-> If a wire has very low resistance, it will start to glow after heating

• this is how incandescent lightbulbs work

  • the tungsten filament in an incandescent light bulb only works because it’s inside of a vacuum inside of the light bulb – otherwise, it would catch fire in open air.

Applying Ohm’s Law to A Flash Light

• Common flashlight has two batteries connected in series

• Total voltage of those two batteries is 3 volts

• Lightbulb that flashlights typically use has resistance of 4 ohms

• So current is 3 volts divided by 4 ohms, a.k.a. .75 ampere a.k.a. 750 milliamperes

• So 4,680,000,000,000,000,000 electrons are flowing through the lightbulb per second

• but resistance can get higher as bulb heats up

Watts

-> Named after James Watt, better known for work on steam engine

Watt’s are measurements of power that can be calculated as:

If:
I = Current (in amperes)
E = Voltage (electromotive force)
P= Power/Watt

Then:
P = E x I

Calculating Wattage

• Multiply voltage by current to get wattage

4.5 (Switches)

Switch: Controls whether electricity is flowing in a circuit or not.
On/Closed: when a switch allows electricity to flow
Off/Open: when a switch doesn’t allow electricity to flow
-> A closed switch allows allows electricity to flow

Switches are binary (on/off) -> either they’re open or closed, like the binary codes invented by Morse and Braille.

Binary codes and simple electrical circuits are similar, and this is important.