E&M

Introduction

E&M (electricity and magnetism) is a wonderful physics topic that influences our day-to-day lives. I hope you will find it as fascinating as I do as you read through this page!

Now, there are two kinds of circuits. There are parallel circuits and series circuits. Series circuits have all their components in a single path, or a series. Parallel circuits connect components in different paths. In the image below, a series circuit is shown to the left and a parallel circuit is shown to the right. I know how crunchy it is. I see it. Leave me alone.

SO ANYWAY. In a series circuit, electricity travels from the cathode to the first lightbulb. The total resistance of this circuit is equal to the sum of the individual resistors. Each part of a series circuit is dependent on the other parts: if one part is removed or damaged, all the other parts will turn off. 

In a parallel circuit, electricity has paths to choose from. All components of a parallel circuit face the same voltage.

I know I've been mentioning the word voltage, and I haven't explained what it means. 

Fear not! I shall go over basic vocabulary:

Electric potential energy is the energy stored in a particle because of its location (if like charges are far apart, it is easy to move them towards each other. However, if they are close to each other, it is very difficult to move them closer). 

Electric potential is the amount of electrical potential energy per charge. In other words, it is electric potential energy / charge.

Charge is measured by a unit called the coulomb (C). One coulomb is equal to the charge of 6.25 billion billion electrons. Although that seems like a lot, it's only enough to light a 100-W bulb for a little more than a second.

Voltage is the unit of measure for electric potential. It is measured in volts. If we change the vocabulary from our electric potential equation: 1 volt = 1 joule / 1 C. It is exactly the same as electric potential. 

Electric current is the flow of charged particles.

Ohms are the unit of measurement for electrical resistance.

Amperes (Amps) are the unit of measurement for the rate of a current. Amps = volts / ohms.

In currents, moving charges do work. When charges perform work, electric energy is converted to another form. The rate in which work is performed is called electric power. Watts are the unit of measurement for electric power. Watts = amps x voltage. 

Okay that was way too much vocabulary and not enough stupid jokes. Let me think of something to say to lighten the mood. Did you know that I've always wanted to buy a singular grape from the grocery store. I need it so badly that it hurts. Alright, back to the topic!

Now that you're up to speed, let's continue our conversation about circuits. As I was explaining series and parallel circuits, you probably wondered what would happen if you connected the cathode and anode of a battery with just one wire. You would end up creating a short circuit. In a short circuit, a very high current will flow through the wire and the battery. This will overheat the battery, causing the chemicals inside to expand and possibly even leak. It could also cause a fire from all the heat energy produced. I have an odd feeling that now you want to connect the two ends of a battery on a tree. Please. California is always on fire anyway, you don't have to lift a finger. 

Conservation of charge is a principle that says that charge can be transferred but not created or destroyed. The net electric charge (total electric charge) of an isolated system will never change. An object that is electrically charged either has too many or too less electrons to be neutral. By this I mean, if the amount of electrons is more than the amount of protons, the object is negatively charged. If the amount of electrons is less than the amount of protons the object is positively charged. There are no fractions of electrons, so this amount always has to be a whole number. Going on a tangent, static electricity is the buildup of charges on the surface of a material. When two or more objects touch each other and then retract away from each other, electrons transfer from one material to the other. If the material receiving the electrons is not a conductor, the electrons will stick to it, which creates the buildup of charge. An example is shown on the image below, through my even crunchier mouse art. Send help.

Okay, now that we're briefed on circuits, let's talk currents. There are two different types of currents: direct current (DC) and alternating current (AC).

DC is a type of electric current that only flows in one direction. It's found in phones, cars, TVs, and more. A lot of household applications use DC. The flow of electricity is constant and in one direction, which makes it a bit more practical for these things. The lightbulb experiment we were discussing earlier showed an example of DC.

AC is the real temper tantrum. AC is a type of current that switches directions at regular intervals. Reminds me of teenagers. Parents, welcome to the jungle. AC is used in power lines and household electricity. AC is less dangerous than DC to handle and it is also easier and more efficient. It can travel farther and is used in motors that don't require careful control. 

Okay, I understand that people are probably getting a little restless now. Don't worry, I just have one more thing to say before we can move on to magnetism.

As electrons travel through a material, they bump into other atoms. This makes them relatively slow. In an ideal world, electrons would face no resistance as they traveled through materials. But oftentimes, an ideal world seems impossible. And yet, this aspect can exist! Superconductors are materials that conduct electricity with zero resistance and zero waste heat! Unfortunately, the superconductors discovered so far only work when they are forced to - with extremely cold temperatures or extremely high pressures (or even both). Science, what the heck. Humanity was just starting to have fun. 

Now, magnets have more than poles. They have fields. Magnetic fields are the energized space around magnets. They are formed by electric charges, specifically made by electrons. Magnetism is created by electron spin and electron revolution (spin is rotating about your own axis and revolution is rotating around another object). Most of the time, electron spin is the main reason for magnetism. Each spinning electron is a tiny magnet, and when there are many spinning electrons, your magnet gets many times longer. Well, this is as long as they are spinning in the same direction. If they are spinning in different directions, their fields cancel each other out. This is the reason why most materials are not magnetic: their electrons cancel out each other's magnetic fields. However, in certain materials, especially iron, the fields don't entirely cancel out. Iron atoms have four electrons whose field is not canceled out. Thus, many iron atoms create a magnet. In iron, individual atoms cluster together due to their magnetic fields. These fields are called domains. Each magnetic domain is magnetized and has billions of atoms in it. However, they are microscopic and numerous in an iron block.

The funny thing is, no matter how much I spin, magical things don't happen. What's up with that? 🤔

If you stroke a piece of iron with a magnet, its domains align. You can actually hear the domains click together, which is literally epic and is probably one of the coolest things you could ever hear. In fact, it's so cool that you should watch this video to hear and understand magnetic domains. 

Electricity and Magnetism are Related

Electric currents have magnetic fields that appear as circular lines around the wire. When the wire is looped, the field becomes bunched up inside it, making it stronger. If you put a piece of iron inside this loop, the magnetic domains align and a strong magnetic called an electromagnet is formed. The strength of an electromagnet can be increased or decreased by altering the amount of current going through the coil. Strong electromagnets are used in the maglev train. Magnetic coils on the guideway repel large magnets under the train, which allows it to levitate just a few centimeters. The train is propelled forward by altering the current in the coil (and thus altering the magnetic polarity). Because of this, the track pulls the train forward from the front while simultaneously pushing it from the back. Again, this is totally epic. If you'd like to explore more, you can watch this video. It is a little bit complicated but very enjoyable nonetheless.

Now, if electricity influences magnetism, why can't magnetism influence electricity? Electromagnetic induction is the property that electric current can be produced in a coiled wire just by moving a magnet around in it. However, pushing a magnet inside a coiled wire gets more difficult with each added coil. Pushing the magnet inside the coil creates voltage, which creates current. The current creates an electromagnet, which repels the magnet being pushed inside. In a mathematical sense, we have a nasty looking equation: the voltage induced = number of loops * change in magnetic field / time.

Charged particles experience magnetic fields, and thus, rays of charged particles bend when exposed to magnets. Switching the direction switches the direction of the bend, as shown in the images below (mouse art is really hard guys).