Welcome to professor mad Electronics for beginners
To day we are going to learn about resistors
We know
Electrical resistance is opposition to the flow of current in an electric circuit:
The resistor's resistance limits the flow of electrons through a circuit.
This is a conductor, assume it has zero resistance.
If we apply a voltage difference, Then the electrons starts to move through the conductor,
A moving electron flow is a negative current flow
We can measure the amount of current using an ammeter,
Here we have very high current, because the conductor has no resistance to slow down the electrons,
they move at full speed.
Let's consider another conductor,
but it has a resistor.
Les't apply the same amount of voltage like the first one
electrons start to flow.
electrons have another option, they have to go through the resistor.
What is the ammeter reading ??
Its less than first reading,
Because the resistor limits the electron flow.
Lets try another conductor.
that has two resistors in series.
current flow has to pass both obstacles.
so the ammeter reading is lesser than earlier.
Likewise we can add more resistors in series and increase the resistance,
This is the symbol of a resistor.
The total resistance is now r1
If we add another resistor, that has r2 resistance,
the total resistance becomes r1+ r2
lets add another r3 resistor in series.
The total resistance increase further more.
Now the total resistance is r1+ r2+ r3
So in general
the total resistance of the series resistors are equal to the sum of individual resistance.
Let's go back again,
we know series resistors reduce the current.
Assume,
this resistor, only allows i1 current to go through it.
Now the ammeter reading is i1
What happens if we connect two resistors that has same resistance in parallel.
and apply the same voltage across those.
Each resistor allows i1 current to go through it
Now the ammeter reading is i1 + i1 = 2i1
The current has increased.
That means the total resistance has decreased.
using parallel resistors we can reduce the resistance.
Look at this circuit
V, R and I are the voltage, resistance and current between the points A and B.
If we add an R1 resistor between point A and B.
it will pass i1 current through it, current
Current has no other way to go from A to b
so the total current I is equal to i1.
Using the ohm's law, we can replace the i by using v and R .
We can remove the term v from both sides.
We are getting an equation like this…
Right.
let's add another resistor parallel to the r1.
like this,.
This new r2 resistor allows i2 current to pass it.
The current has two ways to go from a to b.
The total current is equal to the sum of these two currents. i1 + i2.
We can replace the i using ohm's law
and simplify the equation like this.
We can keep adding resistors and
continue this for more parallel resistors.
for 3 parallel resistors we can build a equation like this.
In a parallel resistor circuit,
the inverse of the total resistance is equal to the
sum of the inverse of each individual resistor.