Charge

Charge is a characteristic unit of matter.

In an atom an electric charge occurs whenever the number of protons in nucleus is greater than the number of electrons surrounding that nucleus. If the number of protons is greater than the number of electrons then the atom is said to be positively charged. If the number of electrons is greater than the number of protons then the atom is said to be negatively charged.

Now just think are you using a charge right now.? the answer is yes.

The monitor right in front of you uses a charge to emit light of various colours.It also controls the light so that it appears in the form of words and symbols in front of you.(If you are using a CRT monitor.. Not in the case of LCD monitor).

Now lets see interesting animated representation of charge.

We know that a charge can be classified as

• Negative charge-Electron
• Positive charge-Proton
• Neutral or no charge-Neutron

In the below representation an electron is released or triggered from electron gun.

• Consider a CRT monitor. Here if we want to display a dot in centre of screen the deflection plates are not given any charge.The electron travels a flat path.
• Now if the dot has to appear in top of screen (or) above the centre positive charge is given to the top plate.So the electron is attracted by positive charge in top plate and repelled by negative charge in bottom plate.
• If the dot has to appear below the centre(or) bottom of screen,. positive charge is given to bottom plate and negative charge is given to top plate. Pictorial Representation is shown below.

Now let us define Coulombs Inverse square law for charges:

When two charges are separated by a distance r between them,then the force is directly proportional to the product magnitude of charges and inversely proportional to square of distance between them.

Let q1,q2 be two charges.separated by a distance r .

F= q1q2/(4*pi*e*r^2) Where e( epsilon) is the permittivity.

Effects Of Electric Current

When electric current flows in a circuit,it produces various effects such as

• Heating Effect
• Luminous Effect
• Chemical Effect
• Magnetic Effect

Out of the above four effects Heating effect and magnetic effect are predominant.

Heating Effect:

In every electric circuit there is a resistance which opposes the flow of current.In order to overcome this resistance and for flow of current, an energy is expended. Here the expended energy appears as heat, causing the heating effect.

The expended power is given by

P=I^2 R
Where I is the current
R is the resistance..

Magnetic Effect:

When a current flows through a conductor it affects the magnetic materials near it or surrounding it.

We can prove this effect with a simple experiment.

Take a flat cardboard and pass a conductor through the board.Connect a battery to the free end of the conductor. Place some iron filings over the cardboard in random fashion.

Now,when no current flows through the circuit the iron filings remain as you placed with out any order(in random manner)

When supply is given using a battery and when current flows through the circuit,you can see the iron filings arranged in concentric circular fashion. This is due to the magnetic effect produced by current.

Now You might ask why the iron filings are arranged in concentric circular fashion..

Consider a simple example... When you throw a stone into a well the wave propagates in the form of concentric circles. similarly when current flows the iron filings are arranged in concentric circular fashion.


From this experiment we can conclude that:

• A conductor carrying current produces a magnetic field.
• Direction of magnetic field depends on direction of current flow.
• The field is in the form of concentric circle.
• The direction of field is perpendicular to the direction of conductor.

The last and final conclusion can be proved from cork screw rule.

Consider the tip of right handed screw. If the screw is to move forward,it has to be rotated or turned clockwise.If the screw has to move backward it has to be rotated in anticlockwise
(or) Counterclockwise direction.

The relation between current and magnetic field is same as above.
The direction of current is same as, the way the tip of the screw moves(ie forward or backward movement). The direction of magnetic field is same as the direction of movement of head (clockwise or counterclockwise).

Basics Of Electricity

Now lets see some basic concepts involved in Electrical Engineering which includes Current,Voltage,Potential Difference, Emf and Ohms Law.

We often use the term current in our day to day life.Lets see the definition of current

Current:

Current is defined as the flow of electric charge between two points of a section (or) a conductor.

We very well know the unit of charge. Suppose if u don't,The unit of charge is COULOMB.

The unit of current is Ampere.

From above two statements we can conclude Ampere= Coulomb/second.

Now lets define what is ONE AMPERE:

One ampere current is defined as the rate of flow of one coulomb of electric charge through a section for one second.

Voltage:

A voltage can be defined as the potential difference that exists between two points.

Voltage can also be defined in terms of the energy required to further charge the body (or) Potential Energy per unit charge on the body.

Therefore we can define ONE VOLT as:

The body is said to have a potential of one volt if 1 joule of work is done to put 1Coulomb of charge on a charged body.


Potential Difference:
If two water tanks having water at different levels are connected together using a pipe,then water will flow from higher level to lower level,till the water level in two tanks are equal. When the water levels in tank (or) beaker is equal,all flow will stop.

Now same concept is applied to electricity. If two points in a electric circuit are at different electric potential and if the two points are connected through a wire or a conductor,current will flow from higher potential to lower potential and try to equalize the potential between the points.

Electro Motive Force:

Electromotive force of a device is defined as the energy per unit charge provided by device to the circuit.

Electromotive force is also defined as the difference in electric potential between the terminals of source of electricity(eg:battery from which no current is supplied to circuit)

Suppose If Q is the unit charge provided by the device and W is the energy then

EMF=W/Q. Its unit is Volt (or) joules/coulomb.

OHM'S Law:

According to Ohms law, the potential difference that exist between two points of a conductor is directly proportional to the current through the same conductor,provided the temperature remains constant.

Ohms law: V directly proportional to I at constant temperature.

V=IR where I-> current through the conductor
R-> Resistance of the conductor

The greatest disadvantage of ohms law is, It holds good for constant temperature conditions. And it is not applicable to varying temperature conditions.

Dc Motor-Principle

We have often come across the term Motor.But many of us don't know what exactly is a motor? And What it does? In this section lets see what is a motor and how motor works..

Motor:
Motor is a device which converts given electrical energy into mechanical energy.

So how the motor converts electrical energy into mechanical energy?

Before going into the principle of electric motor, we have to know a basic rule:FLEMING'S LEFT HAND RULE.

What is Flemings left hand rule?

Flemings Left hand rule shows the direction of the motion of the conductor carrying current in the magnetic field. (or) left hand rule shows the direction of thrust on the conductor carrying current in magnetic field.

According to LHR... The thumb,first finger and middle finger of left hand is held mutually perpendicular to each other as shown in fig.

-> First finger shows the direction of field.

-> Middle finger shows the direction of current.

Then
-> Thumb shows the direction of motion of conductor.



Principle Of Motor:

The working of motor is based on the principle that whenever a current carrying conductor is placed in a magnetic field it experiences a force in the direction as shown by flemings left hand rule.

The magnitude of resultant force is given by:

F=BIl Newton

where
B is the Magnetic Field.
I is the current carried by conductor
l is the length of the conductor.

The principle of motor diagram is shown above.