All electrical circuits have three fundamental electromagnetic properties which are spread throughout
the entire circuit.
First, we have resistance.
Here, resistance impedes the flow of electric current.
In simpler words, it makes it harder for current to move through a material.
As a result, electrical energy is not lost but transformed into heat.
Now, this is why devices like light bulbs or phone chargers often feel warm during use.
And we have the capacitance.
Capacitance stores energy in an electrical field between two conductors.
A key characteristics of a capacitor is that the voltage across it cannot change instantly.
Now think of it like filling a bucket with water.
You can't fill it immediately.
It takes some time and we have the inductance here.
Inductance stores energy in a magnetic field when current flows through a coil or a wire.
Here the important point is that the current through an inductor cannot change instantly.
So you can imagine like pushing a heavy object, it resists certain changes in moment.
Now, because it takes time to build up an electrical field in a capacitor, capacitance slows down
changes in voltage.
Now similarly, it takes time to build up a magnetic field in an inductor.
So inductance slows down changes in current.
Now these two time dependent behaviors, along with resistance, together form what we call impedance.
Impedance simply means resistance to change, whether it's a change in voltage or a current in a computer
circuit.
This impendence slows down the fast switching of electrical signals.
Meanwhile, the pure resistance consumes electrical power by turning it into heat.
In this lecture, we will mainly focus on the general timing characteristics of a resistance, capacitance
and inductance.
Discussions about power consumptions will be saved for more advanced lectures.
Now, to better understand the real world effects of these properties, we will now look at the discrete
electronic devices that are designed to introduce these properties at specific locations in a circuit.
Now these devices are the resistors for resistance, capacitors for capacitors, and inductors for inductance.
They all belong to a broader category called passive components.
Now passive components are part of Circuit that cannot be actively controlled electronically.
Instead, they simply store or consume energy without adding any external energy or making decisions.
Now here you can see the standard circuit symbols for the passive devices we will discuss, which is
switch.
A switch simply opens or closes a circuit, not turning the current flow on or off 1 or 0.
We have the resistor here.
This is a resistor, limits the current flow and produces heat.
Capacitor.
Capacitor stores energy in an electric field and resists certain voltage changes, and inductor stores
energy in a magnetic field and resists certain current changes.
A switch can be in one of the two positions.
It is either open or closed.
In the open position, there is no connection between the two ends of the switch like this one.
And therefore no electrical conduction occurs.
No current can flow through the circuit, but.
In a closed position, the connection between the two ends are complete, allowing the electricity to
flow freely throughout the switch and the rest of the circuit.
Now this symbol you can see here typically represent a manually activated switch.
This means it is operated by a human hand, like flipping a light switch on a wall.
And in the upcoming lectures titled transistors, you will learn that the computer uses transistors
instead of manual switches.
Now, these transistors act as electronic switches that can open or close automatically without human
interaction.
Now, by controlling these electronic switches, computers can implement on off logic, which is fundamental
building blocks of all digital operations inside a computer.
A resistor is used to limit the amount of current in a specific location within a circuit.
By restricting the current flowing into a capacitor or an inductor, a resistor influences how long
it takes for these other devices like capacitors and inductors, which will be discussed in detail later
to store energy.
The amount of resistance is usually carefully chosen, together with the amount of capacitance or inductance,
to create specific timing characteristics in the circuit.
Resistors are also used to limit the current flowing through sensitive devices, ensuring that the current
stays at safe, non-destructive levels as a resistor limits current, it irreversibly transforms the
electrical energy into heat, unlike capacitors or inductors and resistors, does not store energy.
They simply convert it into heat without returning it to the circuit later.
The relationship between voltage and the current for a single resistor is given by Ohm's Law V.
Here is the voltage difference across a transistor at time T is time here I t.
Here is the current flowing through it at the t time.
R is the resistance of a value of the resistor, so the resistor values are specified in ohms.
The symbol is this.
Now the circuit I draw here illustrates two resistors connected through a switch to a power supply,
which delivers five volts.
The Greek letter ohm stands for ohms and kilo.
Ohm means thousands ohms.
No thousand ohms.
Now, since current flows only in a closed path, no current flows until the switch is closed.
Now in this diagram you can see five volt power supply provides a constant voltage of five volts to
the circuit.
Once the switch is closed and we have the switch here initially open, meaning no current flows.
Now when the switch is closed, it completes the circuit, allowing the current to flow from the positive
terminal of the battery through the resistors and back to the negative terminal.
We have the resistors here, uh, one kilo ohms and 1.5 kilo ohms.
These two resistors are connected in series, meaning the same current.
In this case, I passes through both resistors one after another.
In series circuit resistance adds together to form the total resistance.
Now the arrow labeled here I shows the direction of the current flow from the positive terminal of the
battery through the throat switch.
Then the true through resistor and finally back to negative terminal.
Now, because the resistors are in series, the five volts from the power supply is divided across the
two resistors based on their resistance values.
Now across 1.0 kilo ohms which is 1000Ω resistor which is between A and B, the voltage drop is 2.0V
across the 1.5 kilo ohms, which is 1500Ω resistor.
Between B and C, the voltage drop is 3.0V.
The sum of these voltage drops, which is two or actually this 2.0V plus 3.0V equals to the total supplied
voltage 5.0V satisfying the Kirchhoff's voltage law.
So we have points A, B and C point A is where the current enters the first resistor.
Point B is the junction between the two resistors, and point C is the end of the second resistor returning
to the power source after the point C.
Now in series connections, current is the same through all components, but the voltage divides according
to resistance.
Now the higher the resistance, the higher the voltage drop across that resistor.
Now no current flows when the switch is open like this.
But we make it like this.
Then this is constantly flowing like that, right?
And in this circuit here we have five volt power supply which supplies a constant five volts to the
circuit.
When the switch is closed.
Right now it is open.
When the switch is closed it completes the circuit allowing the current to flow.
We have the two resistors here again.
Now what is different than previous one.
Right now that's because we have arranged them in a parallel connection, meaning they are connected
side by side across the same points, which is A and C and voltage across resistors in parallel circuit.
Each resistor experiences the fully supply voltage.
Here.
The both resistors here have the same five volts, five volts here again across them.
And we have the current current I2 and current I, i1 and i2.
This is the total current I t splits into two paths at the point a i1 flows through this one kilo ohm
resistor, but I2 here flows through this 1.5 kilo ohm resistor.
Now, using Ohm's law, we calculate the current through 1000 ohm resistor, which is I1 is equal to
5.0mA and current through 1.5 kilo ohm resistor is 3.3 million amperes.
And the total current supplied by the source is 8.38.3 milli amperes.
And yeah, that was pretty easy, right?
Now, in parallel connections, the voltage remains the same across all branches, but the current divides
based on the resistance of each circuit.
The branch with lower resistance allows more current to flow, while the branch with higher resistance,
in this case 1.5 kilo ohms, allows less current to flow.
Here the behavior follows Ohm's law.
When resistance decreases, current increases for a given constant voltage and for the power distribution
side.
Each branch consists, consumes electrical power independently, and the total power consumed is the
sum of the power across all branches.
Now, in parallel circuits, voltage is constant across all paths, but current splits based on resistance.
Lower resistance branches draw more current and the higher resistance branches draw less current.