Hey there, guys, Paul here from TheEngineeringMindset.com. In this video, we're going to be discussing
electrical current. We'll be looking at what is current, the different types of current, how to check the ratings
of your electrical devices. As well as how we use safety features to save you from being electrocuted. Current is the flow of
electrons in a circuit. To use electricity, we need electrons to flow in the same direction around a circuit. We usually use copper
cables to form the circuit because the atoms that make copper have a loosely bound
electron in their outermost, or valance shell, which is free to move
around inside the metal. This free electron is very easy to move, which is why copper is so popular. It's so easy to move that it will naturally just move to other copper atoms by itself, but this occurs randomly in any and all directions which
isn't useful for us. For us to make use of this, we need lots of electrons to flow in the same direction along the circuit. We can then place things like lamps in the way of these electrons
so that they flow through it and then they generate
light and heat, etc. To do this, we need to
force the electrons to move and we can do that by applying a voltage. Voltage is the pushing force. It's like pressure in a water pipe. The more pressure we have, the more water can flow, the more voltage we have, the more electrons can flow. We covered the basics of voltage in detail in a previous video. Do check that out, link's in the video
description down below. So we need a lot of electrons
to flow along a circuit and through our lamps to
get them to shine brightly. However, the cable and
lamps can only handle a certain amount of electrons
passing through them. Just like a pipe is rated
to handle a certain amount of water passing through
it or a certain pressure. If it exceeds this, then the pipe will burst. Likewise, if too many electrons pass through the cable or the lamp, then they will just burst or burn out. We refer to the flow of
electrons as current, and we measure this in
the unit of Amperes, although you'll usually
just hear people say Amps. This is represented with a capital A. For example, this fuse has
a three and a capital A, which means it's rated
for three amps of current. We'll look at how we use
fuses later on in this video. If you look on the plugs
of your electrical devices, you should find labels
from the manufacturers, which tell you what the
product is designed to handle. For example, this laptop charger tells us that for the device to work, it needs an input of
between 100 and 240 volts and 1.5 amps of AC, or
alternating current. The charger will then convert this to give an output of 19.5 volts and 3.3 amps of DC, or direct current. AC and DC are different
types of electricity. The plugs in your homes will provide AC, or alternating current. In this type, the electrons do not flow
in a continuous loop. They instead alternate between moving backwards and forwards, just like the tide of the sea. Your electrical devices, like laptops and mobile phones, will use DC electricity,
or direct current. In this type, the electrons
do flow in only one direction, much like the flow of water in a river. We transport electricity from the power stations in
AC, alternating current, and send this to our cities and homes. We use AC here because it can be transported very efficiently and over much greater distances than if we were to use DC, direct current. We can also very easily increase or decrease the voltage
using simple transformers. We've covered how transformers
work in our previous videos. Links down below for that, do check them out. We mostly use DC, direct current, in the circuit boards of
small electronic devices, like laptops, mobile
phones and televisions. That's because DC is easier to control and allows circuits to be
smaller and more compact. Many appliances will use a
combination of AC and DC. For example, a washing machine will use AC for the induction motor, which is used to spin the
tub with the clothes in, but the circuit board which
controls the settings, the lights, the timers, as well as how fast the motor spins, will use DC power. We can convert AC to DC using an invertor. This is extremely common in electronics. We covered how inverters work previously. Links down below if you want to watch and learn about that also. People often refer to a river or the tide of a sea as
having a strong current. It's very similar to electricity. A river with a lot of fast flowing water is said to have a strong current. The same with electricity. A cable with a lot of electrons flowing through it has a high current. A river is able to handle a certain amount of water flowing through it, but if more water enters than the river can handle, then the river will burst its banks. The same with electricity. A cable will burst and burn out. Therefore, manufacturers need
to be able to test cables and lamps to find out how
much current they can handle. We also want to be able
to see how much current is flowing through our circuits as well as being able to calculate this. We can measure this using an ammeter where we measure the flow of current in the circuit using the units of amps. So what is an amp? One amp is equal to one coulomb, and one coulomb is equal to approximately six quintillion, 242 quadrillion
electrons per second. What does that mean? Another way to look at this is that to power this 1.5W lamp
with a 1.5V battery, approximately, six
quintillion, 242 quadrillion electrons need to flow from the battery and through the lamp every second for the lamp to stay on. If we reduced the voltage, then less electrons will move and the lamp will become dimmer. If we increase the voltage, then more electrons will flow and eventually the lamp
will not be able to cope so it will burst or burn out. So to measure the current in a circuit, we need to connect an ammeter in series so that the current flows through it. Think of it like a water meter. The water need to flow
through the water meter for us to know how much
water is flowing in the pipe. Likewise, we need the electrons
to flow through our ammeter so that we know how much electricity is flowing in our circuit. Instead of using an ammeter, we're going to use a multimeter as we can do a lot more with this device. I'll leave some links down
in the video description where you can pick up a
good multimeter cheaply. I highly encourage you to get
one of these for your toolkit. They're pretty cheap and are very useful. If we connect a lamp
to a battery in series, then we can measure the current using a multimeter by connecting it in series. If we connect this 1.5 volt battery and this lamp, which has a resistance of one Ohm, then we get a current of 1.5 amps, which means nine quintillion,
636 quadrillion electrons are flowing through the lamp every second. Because it's in series, all the electrons in the circuit are flowing along the same path. So that means we can move
the multimeter to here and we get the same reading. If we add another lamp
to the circuit connected, again, in series, the lamp also has a resistance of one Ohm, then we are adding more
resistance to the circuit, so the electrons are slowed down. In this case, we get a
reading of 0.75 amps, which means four quintillion,
818 quadrillion electrons are flowing per second. This is in series, so again we can move the multimeter and we get the same reading. If we now connect the circuit
with two lamps in parallel, both with a resistance of one Ohm and connect this to a
battery of 1.5 volts, then in the main wire, to and from the battery, we get three amps. But on the branch of each lamp, we get 1.5 amps. That's because the path for
the electrons has split, so the electrons are shared with some flowing through lamp A and some flowing through lamp B. In this example, both lamps have an equal resistance so the current is split equally. But if the lamps are of
different resistance, then the current is split unequally. For example, if lamp A has
a resistance of one Ohm and lamp B has a resistance of three Ohms, then in the main wire, we get an amp reading of two amps. In the branch for Lamp A, we get 1.5 amps, and in the branch for
lamp B we get 0.5 amps. As you can see, lamp B is dimmer because
there is a higher resistance so less electrons can flow through it. In both cases, the amps in the branches will add up and are equal to the total current flowing in the main wire to and from the battery. Now, I mentioned that lamp B was dimmer because the resistance was higher. If you remember, I also said that cables and lamps, etc., are only rated to handle a
certain amount of current. If it exceeds this, then they can burn out. So restrict the amount
of current that can flow, we can add resistors into the circuit or into part of the circuit. These act like speed bumps
and slow the electrons down. Resistors are like putting
a bend into a garden hose. The kink adds resistance
to the flow of water, which reduces the amount of water that can flow out of the hose. Similarly, we can add
resistors to the circuit and it slows down the electrons. For example, this LED is
rated at 25 mA and 3.3 volts. But our battery is rated at nine volts. So if we were to connect
the LED to the battery, it would just burn out because it can't handle that much voltage and current. So to stop the battery from burning out, we need to place a
resistor into the circuit. In this case, we'll use a 270 Ohm resistor to bring the voltage and current down to a
safe level for the LED. If you want to see how much current is flowing through your
electrical devices at home, then you can use one of
these cheap energy meters. You simply plug your appliances into it, and it'll measure the voltage, amps, watts, power factor, etc., and you can then even calculate how much it costs to use the appliance. I recommend you have one of these. They're a great little
device for your toolkit. I'll leave some links down below for where you can get a
good one very cheaply. So we saw earlier that
we can use resistors to reduce the amount of
current flowing in the circuit and protect our devices. Another thing we can use is a fuse. Fuses in a basic sense, have a thin piece of wire inside them, which is rated to handle a certain amount of current flowing through them. In this case, this one is
rated to handle three amp, or 19 quintillion, 272
quadrillion electrons per second. The fuse acts as a weak point and it's very cheap to replace. So if too much current
flows in the circuit, it will burn out and
open to break the circuit and protect the more expensive
electrical components. You can find these
melted on circuit boards and you can also find these
built into some plugs. For example, this plug
from the UK has a fuse built into it to protect
the electrical device. Another device we use, and you've probably seen
these in your homes, this is the circuit breaker. It's essentially a switch
that will automatically open to break the circuit if
it detects too much current or too many electrons flowing through it. It's rated to handle a certain amount of electrons flowing
through it per second, but it measures this using heat or an electromagnetic field to detect and act on if too many electrons
are passing through it. If it exceeds this, then it will open to break the circuit. If for example, we slowly
add load to a circuit, then the bimetallic plate will detect this slow rising current because the current causes it to heat up. As it approaches the designed rating, it will break the circuit to cut the power and protect the cables and devices. The load can then be reduced and the circuit breaker reset, unlike a fuse. Another extremely important
function is if for example, you touch a live component and receive an electrical shock. There will be a sudden surge in current and the circuit breaker can detect this and cut the power almost instantly to stop you being electrocuted and save your life. Okay, that's it for this video, but if you want to continue
learning about electricity and electrical engineering, then just click one of these
videos on the screen now and I'll catch you there
for the next lesson. If you have any questions, let me know in the comment
section down below.
