Electricity

How electricity moves through a wire

Concudctive materials

A copper wire contains trillions and trillions of copper atoms. Being the atomic number 29 on the periodic table, each copper atom has 29 protons and 35 neutrons, forming the nucleus. It also has 29 electrons around the nucleus. In the outermost shell of the atom, 1 electron is free to move around between different copper atoms. Due to ambient thermal energy, this process happens when the copper wire is at rest and unconnected to an energy source. On the bigger scale, the outcome is the same because some atoms move left, while others move right, effectively cancelling each other out.

When an electron leaves the copper atom, it has 28 electrons now compared to its 29 protons, so it is positively charged.

Adding power

Now, when we connect our copper wire to a battery, the negative charge coming from the negative terminal enters the wire and pushes against the positively charged copper atoms. Like putting 2 positive ends of 2 magnets together, positively charged atoms are repelled by negatively charged ones. This introduction of negative charge causes a domino effect that nudges the electrons in a particular direction. Each electron is only moving a small amount.

Because our battery has both a positively charged end and a negatively charged side, it has an electric field. When we connect our wire, we can direct the electrical field through the wire. The electrons still move randomly, but the electrical field causes them to drift toward the positive terminal. As those electrons travel through the wire, it creates a magnetic field around the wire.
- ex. if you put a compass next to a wire that has flowing electrons, it will disrupt the direction.
- this fact is what allows us to create electrical magents, and is also used to drive electric motors.

Electrical Units

Voltage (V) - Pressure

Voltage is like pressure. When we measure voltage, we are measuring the difference between 2 points (such as the nodes of a battery)

If you attach a multimeter to the 2 ends of a long copper wire and apply 10V, the voltage will gradually decrease as it travels from negative to positive. However, the current (amps) is the same at each point.

this is due to the fact that the magnitude of the electrical field inside the wires is the same

Amps (A) - Flow

Flow rate of electrons

because we're talking flow, we can say things like "a current of 1 amp is flowing through this wire"

When we're talking water, we describe flow in terms of quantity/unit of time. With electricity, we have the unit of Coulomb, which is a measurement of electrical charge.

1 Amp = a flow rate of 1 coulomb/second
1 Amp is equal to a flow of 6.2 quintillion electrons per second

Watt (W)

Watts measure the rate of energy transfer

in mechanical terms, energy transfer is work (and is measured in joules)

In electricity, energy (joules) is transferred when a voltage (𝑉) moves charge (𝑄) through a circuit.

One watt is the rate at which electrical work is performed when a current of one ampere (A) flows across an electrical potential difference of one volt (V)

this means that the watt is equivalent to the volt-ampere

To understand watts, you must first understand joules

the amount of joules equals the product of the force strength (N) and the distance travelled
- ex. when a ball is held above the ground and dropped, the work done by the gravitational force on the ball as it falls is positive, and is equal to the weight of the ball (a force) multiplied by the distance to the ground (a displacement)
- a newton is a measure of force. A newton-metre is dimensionally equivalent to a joule.
a joule is a measurement of work. It is the product of the amount of force applied and the distance travelled. One joule is equal to the amount of work done when a force of one newton displaces a body through a distance of one metre in the direction of that force.
1 Watt = 1 joule/second

Examples

A person having a mass of 100 kg who climbs a 3-meter-high ladder in 5 seconds is doing work at a rate of about 600 watts. Mass times acceleration due to gravity times height divided by the time it takes to lift the object to the given height gives the rate of doing work or power.[i]
A laborer over the course of an eight-hour day can sustain an average output of about 75 watts; higher power levels can be achieved for short intervals and by athletes

Analogy: Icing Dispensing Bag

Voltage (V) = Pressure on the Bag The more you squeeze the bag, the more pressure you apply, just like voltage "pushes" charge through a circuit.
Current (I) = Flow of Icing The amount of icing coming out per second is like current—how much charge is moving through the circuit per second.
Resistance (R) = Nozzle Size A smaller nozzle restricts flow (higher resistance), while a larger nozzle allows more icing through (lower resistance).
Power (W) = Rate of Icing Applied to the Cake The faster you apply icing (more flow at higher pressure), the more work is done per second, just like electrical power (watts) is how much energy is transferred per second.
The total work (Joules) done is like the amount of icing applied to the cake.
The force strength (pressure from squeezing) is analogous to voltage.
If you squeeze harder (increase voltage), more icing (current) comes out faster, meaning more power is applied.

Analogy: Water tank

If we had a water tank and a valve, we could put a meter on the valve. That meter is comparing the pressure inside the pipe with the pressure outside (ie. atmospheric pressure). When the tank is empty the meter reads zero, because the pressure inside the tank is the same as the pressure outside.

Ohms - Resistance

Any substance will conduct electricity if you put a big enough voltage across it: even air, which is normally an insulator, suddenly becomes a conductor when a powerful voltage builds up in the clouds—and that's what makes lightning.
When it comes to electricity, a binary label of conductor or insulator is useless, since anything with enough voltage will conduct electricity (even plastic). Instead, a better way to think about it is in terms of resistance level. Metal has low resistance, while plastic has high resistance.
- Resistors allow us to precicely control how much electrical current passes through it.
- an object with low resistance means that electrons are able to move more freely throughout it.
Ohm's Law - resistance is defined as the voltage required to make 1 amp flow through a circuit.
- Resistance can be determined by hooking up a multimeter to the circuit. The device feeds a known wattage current through the circuit and back into the device, and measures the volts that are received back into it.
level of resistance is measured in Ohms (Ω)
If you attach a multimeter to a piece of resistance wire, the further away you attach it the higher your resistance will be
- ex. This is how toasters work— basicallly, a lot of resistance wire is used in order to increase the heat.

Ohm's Law

Ohm's law describes a relationship between Voltage (V), Current (I) and Resistance (R). As long as we know 2, we can calculate the 3rd.

$V = I \times R$

Applications

Incandescent lightbulbs (old-style)

these worked by having a filament with high resistance. The wire was so thin that the electricity has to fight to get through it, resulting in a lot of heat being given off, hence the name
This is similar to how toasters and kettles work. The idea is the same: shoot lots of electricity through an object with high resistance, causing it to heat up.

Analog Volume Knob (ex. radio)

The volume knob is actually part of an electronic component called a variable resistor. When you turn the volume down, you're actually turning up the resistance in the circuit that drives the radio's loadspeaker. With less current, there is less energy to power the loudspeaker.