Hi welcome to professor mad Electronics for beginners
Today we are going to talk about capacitors.
A capacitor is little like a battery.
Although they work in completely different ways,
Capacitors and batteries both store electrical energy.
There are differences
a Battery stores energy in the form of chemical energy,
and converts it to electrical energy.
a capacitor stores charge in the form of an electrostatic field.
In a battery chemical reactions produce electrons on one terminal
and absorb electrons on the other terminal.
But capacitors can't produce new electrons.
Battery provides energy to the circuit.
Capacitor draws energy from the circuit,
stores and then releases the energy, when it is needed.
To understand the capacitor, let's look into an example
This is a water tank,
it is connected to a pipe line,
one end of this pipe line is connected to a rubber balloon.
And there is a control valve to control the water flow.
To convert the energy of moving water to work, we use a rotating wheel
capacitor is like a rubber balloon connected to a water line like this
When the valve is open , water starts to move.
The balloon is expanding until the water pressure inside the balloon
equals to the water pressure in the tank.
Now the balloon is also a water storage
like a mini water tank.
Let's close the valve and disconnect the water tank.
What is happening ??
The water is still moving, until the balloon shrinks to its original size.
Because the water pressure inside the balloon pushes the water out.
This is what happens in the capacitor.
We call this the hydraulic analogy.
Because , various electronic components in a circuit are represented by hydraulic equivalents.
Here, the battery equivalent to the water tank,
electric potential is equivalent to water pressure.
the electric switch equivalent to the water control valve,
Valve control the water flow and switch control the electron flow.
Here the balloon is equivalent to the capacitor.
We saw that, a balloon can store water and supply it when pressure goes down,
Capacitors do the same job, they store the charges
and supply them when voltage goes down.
This is a electrolytic capacitor, they have a negative pin and a positive pin
Negative terminal is marked with a black strip usually.
We can connect capacitor to circuit, parallely like this.
Negative terminal of the capacitor is connected to negative side of the circuit
and positive terminal of the capacitor connected
to positive side of the circuit
lets replace the capacitor by its symbol, for ease of understanding.
A capacitor consists of two conductors separated by a non-conductive region.
This is a non charged capacitor,
here red dots represent the positive charges,
and blue dots represent the negative charges.
Since this is non charged, the number of positive charges equals to the number of negative charges
in each conductor plate.
That means net charge is zero, for each plate.
So no electromagnetic force between Plates
The electron pressure is zero for both
lets name the plates as A and B
and represents the net charge of each plate like this.
Now, we close the switch and completes the circuit.
Electrons starts to move
look carefully,
one electron is going into the plate A ,
now the net charge of plate A is -1.
This new extra electron can't go through the non conducting region ,
So to balance this inequality ,
Plate B releases an electron, and becomes +1.
The total charge of the capacitor is 0 , but inside it has two charged plates
one has a +1 charge and, other has a -1 charge,
it creates an electromagnetic force, opposite to the incoming electron.
but that force is not enough to stop the incoming electrons
from battery,
Plate A and Plate B always have the same number of opposite charges.
When the potential difference between the plate A and B, becomes equal to the
potential difference of the battery, we say the capacitor is fully charged.
no more electrons goes to the capacitor.
Let's try to open the switch, and disconnect the battery.
What is happening ??
Even Though the battery is disconnected,
The capacitor still has the potential to move electrons around the circuit.
Plate A releases its excess electrons , and plate b attracts the electrons at same time.
The electromagnetic force between plate a and be is going to be zero
we call this as capacitor discharging.,
Lets see again,
When the switch is closed, electrons start to flow from the battery.
Capacitor stores electrons, Capacitor is charging.
When the potential differences of capacitor and battery are equal,
no more electrons go into the capacitor.
Capacitor is fully charged now.
When we open the switch and disconnect the battery,
the capacitor is still able to supply current to the circuit ,
until it gets discharged.
This is a capacitor,
one conductor plate has -q charge, and other has +q.
Due to this charge difference, the capacitor's potential difference between two plates is V.
An ideal capacitor is characterized by a constant capacitance C,
defined as the C=Q/V
Capacitance is the ratio of the positive or negative charge Q on each conductor to the
voltage V between them.
Capacitance is measured using Farads.
A capacitance of one farad (F) means that
one coulomb of charge on each conductor, causes a voltage of one volt across the device