Week 1, What is Electricity?

Day 1

Summary of This Lesson

This lesson will introduce you to how electricity flows from one end of a battery to another. Additionally, it will introduce you to what voltage, current, and resistance is, which are some of the properties that deal with electricity. You will also learn about the tools that can help use see the properties of electricity, along with the power that electricity has, which segues into electrical safety.

Lessons for Electrical Training on the website requires a Tinkercad account at www.Tinkercad.com, so if you haven't already, make an account on that website. Also, you can press the "Try Circuits" button in the circuits tab of Tinkercad to get an introduction of how to use Tinkercad's circuit simulation feature.

A Brief Introduction to the Components Used for this Lesson

Now reading about this is great and all, but hit the imbedded link below, it should allow you to play around with the circuit shown above! It is recommended that you go to the "Try circuits" tab in the Tinkercad circuits section to get a feel for how you can use the Tinkercad circuit design feature. You should also have a Tinkercad account, if not, just create one. Press copy and Tinker and you are on your way! Continue to read on while having that tab open.

Now, once you are able to tinker with it, press "simulate" and see what happens.

Great, now get another 9V battery, delete the wires between the resistor and the battery. Then, make a connection between the resistor and the positive side (red wire) of the OTHER 9V battery.

The less relatable analogy:

Imagine that you have two water bottles, one with much more water than the other, and they are hooked together by a hose at the bottom of each water bottle. The water from the water bottle with more water goes into the water bottle with less water. Since the water bottle has more water, the force of gravity makes the water in the water bottle with more water have more force compared to the water in the other bottle. If there was a bigger difference in water between the water bottles, then there is more potential energy (in terms of water, it is pressure). In terms of water, the more pressure you have (the force for a unit of area) increases. To keep things simple, the more pressure caused by more water, the greater the pushing force of the water.

What is Voltage?

This idea of having one area with more stuff going to the area with less stuff is what makes electrons flow. When there are more electrons in one area, and less electrons in another, voltage is present. In a battery, there are two sides. One side has more electrons than the other, just like in the water analogy where one water bottle has more water than the other. In fact, the side with less electrons is made up of positively charged atoms. Opposite charges attract, which is why the electrons go from the side with more electrons to the side with less electrons. This difference in the number of electrons creates a voltage potential, which is basically just saying that there is voltage, or the potential ability for the electrons to flow. In order for the electrons to actually flow, a conductive material like copper in a wire is used to connect the two sides, similar to how the two water bottles were connected by a tube. So the takeaway for voltage is that it is like a pushing force for electrons, and that it is present when one area or point has more electrons than the other. The greater the difference in electrons, the higher the voltage. The higher the voltage, the more pushing force for each electron, giving it more energy.

Now which side of the battery has a lot of electrons and which side has a shortage? The negative side (indicated by black, and is called the anode) has most of the electrons, while the positive side (indicated by red, and is called the cathode) has a shortage. In circuit design, we use conventional flow, which actually assumes that positively charged protons travel through the circuit. Why? Back then, people guessed that protons were the ones flowing in a circuit, but after it was discovered that it was actually the electrons, they decided it was a hassle to change the convention of protons flowing in a circuit. So now in the present time, we use conventional flow, where electricity flows from positive to negative.

What IS resistance really?

You've seen how wires are able to easily allow electricity to flow through it. You can probably guess that a wire barely has any resistance. Now if we had a wire that had much more resistance, like 100 ohms, it would act more like a resistor. A wire is made up of copper, or some other very conductive metal. It has a very low resistance. A resistor can have elements like carbon to resist the flow of current. See what I did there with the words? Never mind. Not only does the resistance of an element matters but if an electron has to force it's way through a resistive material for longer, then there will be less current (electrons per second). The electrons get tired after all that resistance. Here's a circuit you can try out in the imbedded link. Click on the black handle of the blue circle and spin it around and see what happens.

Fun fact: If you drew a very thick graphite line with your pencil and measured the resistance with a multimeter, you'd see the resistance change as the distances change between the multimeter wires (more specifically called probes). That is basically what happens in a potentiometer!

Note: This experiment will be done during the in-person meets. That means that you will be missing out on the graphite experiment :(. But you still have the potentiometer one! YAY!!!

To sum everything up...

Here is a nice circuit in the imbedded link that will relate voltage, current, and resistance and will help sum everything up. By the way, the white box to the left is called a power supply. It can change how much voltage it gives to a circuit. It's like a potentiometer where it can vary it's resistance, except it does that for voltage! Change the voltage from the power supply and the resistance from the resistor to see how current is affected. We'll learn how they are more related later on, so stay tuned.

Also, here are some videos that can also help sum everything up

This person has an accent, sorry about that.

Now for the Boring but Necessary part, Safety

Repeated safety violations will result in you being kicked from the team. Don't worry, as long as you follow the guidelines, and essentially have common sense, you should be good.

• Keeping Safe from Voltage

  • Electrons in a circuit can in fact kill you. Remember how voltage is like a pressure that can be used to push electrons? Well if you have enough of it, say 120 V from a wall outlet, that electricity can go through you, and can stop your heart. Big nope. If that doesn't happen, say you touched only one finger on the outlet to connect the circuit (still don't do this), it can burn your finger severely due to the power that 120 V can create (we'll learn about power later). If you put your finger, or both your hands into the wall outlet, or any high voltage source, you become apart of the circuit, creating what's called a short. That is why electricity can run through you and cause damage. So in short, do NOT create a short. I guess I shouldn't have used the phrase "so in short" there, but I'll keep it because it's a pun.

• Preventing Shorts in circuits

  • You know that wires carry electricity very well. The reason why wires in a normal circuit with resistors, or any other loads like an LED or motor don't burn or blow up is because well, there is resistance and other loads to hinder the flow of electrons through a circuit. Too much current, which is the rate of flow of electrons through a circuit, can create a lot of heat, and can create a fire hazard in more powerful circuits like the ones in FRC robots. So how can a seemingly normal circuit create a fire hazard? As stated in the previous point about voltage, a short can be created which directly connects the two terminals of a battery, or power source together. If a wire, or more realistically, a strand of a wire that was accidentally left hanging, made a connection between the two terminals in a 12 volt FRC battery, then it will burn up. If for some reason, there was a whole wire there, then it would create a LOT of heat. Now, you may have touched a 1.5v battery's ends with your hands together and nothing happened. Why? The voltage is too small to push the electrons through your body, which has a lot of resistance. However, the 120 V outlet has enough energy to do that, so that means that your body is able to act as a conductor to create the short.

• Safety in FRC

  • In the workshop where we build the robot, and during competitions, it is very important to wear safety glasses! Parts may be flying randomly, big or small. You don't want to have those hit your eye, but rather, your safety glasses.

• General Electrical Safety Practices

  • Simply put, always pay attention to what you are working with. If it is a small electronic circuit with low voltage, like 9 volts, there's most likely nothing to worry about... in most situations. Some situations can include components that can discharge a lot of electrons in a short amount of time that can harm you.

Here's the FRC safety manual: 2020-FIRST-Robotics-Competition-Safety-Manual.pdf (firstinspires.org) This is not only for the electrical side of things, but also for everything else. It is worth looking at and reading it.

No short quiz for the first day since that would be lame

Day 2

Summary of This Lesson

This lesson will have the members find out themselves what the relationship between voltage, current, and resistance is in a circuit. Next, they will learn about how that relationship can apply to series and parallel circuits. Of course, there will be a brief introduction to series and parallel circuits.

Lessons for Electrical Training on the website requires a Tinkercad account at www.Tinkercad.com, so if you haven't already, make an account on that website. Also, you can press the "Try Circuits" button in the circuits tab of Tinkercad to get an introduction of how to use Tinkercad's circuit simulation feature.

To Start off, YOU will Create the Circuit for the Lesson!

To start off, you will create a circuit with a 9V battery, a multimeter, and a 400 ohm resistor (change the unit from kiloohms to ohms. By the way, the symbol for ohms looks like a horseshoe, or an omega). Connect all of the components in series, which means that there is only one path for the electricity to take to get to the other side of the battery, which is through all the components. Have the red wire of the multimeter connected to red, and black to black (directly or indirectly, it doesn't matter as long as the directions are right). Oh, and don't forget to set the multimeter option to amperes (amps).

Time to Measure the Voltage, Current, and Resistance of YOUR Circuit

First off, we already know the voltage, it's 9V from the 9V battery. We also know the general resistance of the circuit, 400 ohms from the 400 ohm resistor. Technically, you can still measure voltage and resistance, by for example having the wires of the multimeter connected to both ends of either the battery or resistor and measuring them separately. Current is what we don't know, which is why you have a multimeter in series with all the other components. Remember how a multimeter needs electrons to run through it so that it can "count" how many electrons pass by per second to get current (which is the amount of electrons passing by per second).

After measuring current, think about the numbers. 400 ohms, 9 volts, and if you made the circuit correctly with the right voltage and resistance, a number around 22.5 mA (which is 0.0225 A). Figure out what two numbers when multiplied or divided by each other gets you the third. Keep in mind that the 22.5 mA is actually 0.0225 A, so use 0.0225 when trying different numbers and operations.

Ohm's Law Applied

To see how Ohm's law works in a circuit, let's make our own circuit and test it! Fortunately, you have a circuit that you just made a few minutes ago. For this experiment, replace the 9V battery with a power supply. The power supply's connection to the circuit is the same as the 9V battery. The only thing that we are changing is if we can change voltage or not, which in this case, we can.

Play around with the voltage setting on the power supply, and notice how the current changes. Change the resistance of the resistor, and see how the current changes. What about current? Can you change that independently? Well no. The reason why current changes is because resistance, or voltage, or both changes. So current is dependent on the resistance and voltage.

After every change you make, use one of ohm's law equations, like V=I*R, or I = V/R, and plug in the corresponding numbers from your circuit into the equation and see how the equation(s) basically work out. Remember: V = voltage in volts, I = current in amps, and R = resistance in ohms. If you have a number with a unit next to it that has a prefix, like milli, convert it to a unit without a prefix, like amps from milliamps. You can look up unit prefixes online to figure that out, or use a conversion tool online.

After playing around a bit and plugging in numbers, you may have noticed that more voltage or less resistance means more current. You may have also noticed that less voltage, or more resistance means less current. So in general, if voltage goes up, current goes up. If resistance goes up, current goes down. Now just because you have 1,000 volts doesn't mean you have a lot of current. If you also have 100,000,000 ohms of resistance, according to ohm's law, I = 1,000V / 100,000,000 ohms = 0.00001 amps, or 0.01 mA.

Kirchhoff's Voltage Law

What's with the weird name? Kirchhoff? How do you even pronounce that? Well, I personally pronounce it as Kirk-off. Anyway, what is Kirchhoff's Voltage law? Let me show you this circuit:

Go ahead, try it out and press simulate. Now what happens when you add the voltage readings of the multimeter? You'd probably get something close to 9V, which is the voltage from the battery! That doesn't answer why there are voltage readings for each resistor. You might be thinking "Aren't you supposed to measure the resistance of a resistor, and not the voltage?" Usually that is what we do, but we can also measure the voltage, more specifically, the voltage drop across each resistor. What does that mean? When we measure voltage drop across a resistor or any component, we are looking at how much voltage was dropped, or gotten rid of, by that component. Voltage is like an energy, or a pushing force for electrons. If an electron with that pushing force or energy goes through a resistor, that electron loses energy since it had to use energy to get through the resistor. Since voltage is the energy, and energy was lost, then voltage was lost.

How does the multimeter get the voltage lost, and not the voltage remaining? Remember that voltage is caused by a difference in electrons. You can imagine that in a battery, the side with no electrons has 0V, while the side with all the electrons has 9V. The difference in voltage now, is 9V-0V = 9V. Voltage is relative, so if you had something like 10V next to 1V, the actual voltage difference between those two is 10V - 1V = 9V. In a resistor, one side has for example, 5 volts, and the other side has 3 volts. What happened to the 2 volts? It got used up by the component! That use of the 2 volts can be heat, light, mechanical movement as in a motor, etc.

Looking at the beginning of the circuit (conventional flow), the resistor at the bottom of the circuit, the multimeter reads 4.49v. That means that on the beginning side of the resistor, there is 9V, but at the other end of the resistor there is 9V-4.49V, or 4.51 volts. So, the difference in voltage between the beginning and end of that resistor is 9V-4.51V, giving us the multimeter reading of 4.49V. Going to the next resistor in the circuit, the beginning of that resistor has 4.51V, since voltage (energy) was lost by the first resistor. Doing 4.51V - 2.57V (the multimeter reading), we get 1.94V, the voltage at the end of that resistor. Now you'll notice that the next multimeter reading is 1.92V. Our calculations of getting to 1.94V was a little off, and should actually be 1.92V. The last of the voltage is used up by the last resistor.

That is essentially what Kirchoff's voltage law is. All the voltage being put into a path in a circuit is used up by the components. This means that if you add up all of the voltage used (voltage drop) by every component in that path, it would equal all of the voltage being put into that path. The reason being is that energy (voltage) cannot be created or destroyed. You may or may not have learned about the law of conservation of energy. If not, then you just got the jist of that, with electricity!

Notice how the explanation above said path(s), not circuit. This is a segue into what Kirchhoff's voltage law is like in a parallel circuit, where there are multiple paths.

Now you might be thinking "This is nice and all, especially with the multimeters to see the voltage drops, but what if we don't have multimeters?". Great thought and question. Ohm's law can save the day, and you'll notice later on that you can use Ohm's law for many things. It's like the alphabet but for electronics. Anyway, we know that one of the equations of Ohm's law is V = I*R. The V (in volts) in this case can be used to find the voltage drop, which is equal to the current (I, in amps) going through the resistor/component, multiplied by the resistance (R, in ohms) of that component. So if a resistor had 15 mA going through it with a resistance of 500 ohms, then it would be 0.015 A * 500 ohms = 7.5 volts used up by the resistor. You can essentially drop out the resistor and replace it with any component, and it would be the same concept.

Here's a parallel circuit with multimeters measuring different voltage drops in the imbedded link

Play around with it, change the resistances of the resistors. Notice how there are multiple paths that electricity can take to get to the other side of the battery. The paths being through the right most resistor, the middle pair of resistors, and the left most resistor. Those paths join back together on the other side of the battery, the negative side if you are using conventional flow, or the positive side if you are using electron flow. When looking for the paths of electricity in a parallel circuit, you can start at the positive end of the battery (conventional flow), and whenever there is a split or junction, the splitting off part is a separate path.

You may have noticed that when changing the left and right most resistors' resistances, the voltage drop stays basically the same. Looking at the path that those resistors lie on, you will notice that there are no other resistors, or components with resistance, on their path. Kirchhoff's voltage law says that all voltage given in a path will be used up, and in the cases mentioned, all of it is used up by the one resistor in the path. Voltage usually gets used up when electrons go through resistance, like through a resistor. In real life, wires have some resistance, but barely any. They technically can take away energy, or voltage, in a circuit and turn it into heat. In fact, a resistor, or any component, can get hot if there is a lot of voltage, or energy. If there is a lone resistor in a high voltage circuit, it would end in an explosion, since that is theoretically the only component that can take away the voltage and convert it into heat.

You many of also noticed that when changing the resistances of the middle resistors, the sum of the voltage drops across those two resistors equals the total voltage drop across the path, which basically doesn't change. This situation where there are resistors in series (connected one after the other) is a similar situation to the previous point on Kirchhoff's voltage law for series circuits above.

You may have noticed that each path has basically 9 volts going into it, but there are three paths, so how can a 9 volt battery supply 9*3, or 27 volts? It doesn't, because voltage is relative. What this means is this, the beginning and the ends of each path all have the same difference in electrons. All of the paths share the same "supply" of electrons on one side. On the other side of each path, they share the same amount of lack of electrons. That is why the voltage, or difference in electrons, of each path is the same. Since each path gets 9 volts, you can imagine each of the paths being their own separate series circuit (only one path for electricity) with their own 9V battery.

Kirchhoff's Current Law

Kirchhoff's current law is more understandable compared to Kirchhoff's voltage law, so the hard part is done! So you know how current is the amount of electrons passing by a point per second? There can be different amounts of electrons passing by a point per second at different points in a parallel circuit. What about series? Current actually stays the same throughout in a series circuit, or within the parts of the circuit where there are components in series.

To show Kirchhoff's current law, you can use the multimeters from the last bit about Kirchhoff's voltage law, but use it for current. If you forgot how to measure current with a multimeter, you can look at day one of this week.

Now, using conventional flow, measure the current right after the battery and before the first path. Then, measure the current running through each path, so essentially the currents through the resistors.

It should look something like this:

Add up the currents running through each path, but not the whole circuit. What number seems familiar? In the specific picture above, you may have gotten around 106 mA. If you changed the resistor amounts from the last demo, it will be different, because as we know from Ohm's law, more resistance means less current, and vice versa. So, the currents running through each path when added up equal the current flowing right out of the battery. It makes sense, because if the battery supplies less current (electrons passing by a point per second) than the total currents through the paths, then we would've literally created energy out of thin air, which would be nice, but unfortunately that won't exist. If the battery supplied more current than the total current running through the paths, then we have lost electrons for no reason, and therefore energy.

You may say that voltage is energy, but the more current with the same amount of voltage can mean more energy as well. If each electron has it's own energy that can be used, and there are more electrons, you have more energy (energy/electron multiplied by electrons, electrons cancel out and you are left with energy). Now, current is electrons per second, so it would be more energy per second, which is essentially power, but we'll learn that later!

Now, what is the definition of Kirchhoff's current law? Essentially, it states that the total current entering a junction (which is like an intersection) must be equal to the total current exiting the junction. So, if you had 30 mA and 50 mA going into a junction and forming one path, then the one path has 80 mA of current, since 30 mA + 50 mA = 80 mA. The opposite direction is also true. If 80 mA in one path enters a juction and splits into two, then well, there can be a combination of amperages, but for this example, one path has 30 mA, and the other 50 mA. Again, the current depends on the resistance and voltage.

VERY IMPORTANT!!!!!

This is a very important message. Click the collapsible text because it is that important.

Here are some YouTube videos to sum it all up, with some tips.

I'm sorry to do this to you, but we will need you to take this short quiz. Don't worry, it is only 5 questions, and there is an answer key with explanations at the end that you can see after answering the 5 questions.