Topics covered

Electric ChargeElectric CurrentElectric PotentialElectrical ResistanceOhm’s LawSeries and parallel connection of resistorsElectric PowerElectric Energy & its commercial UnitHeating Effects of Electric Current

STATIC ELECTRICITY

TYPES OF ELECTRIC CHARGES

There are two types of Electric Charges:

Positive Charges

Negative Charges

By Convention,

The charge acquired by a glass rod is called Positive Charge

The charge acquired by an ebonite rod is called Negative Charge

Opposite charges (or Unlike charges) attract each other.

Similar charges (or Like charges) repel each other.

SI UNITS OF CHARGE

SI Unit of Charge is Coulomb, denoted by COne Coulomb is that quality of electric charge which exerts a force of

9 * 109 N on an equal charge placed at a distance of 1 metre from it.

Charge possessed by an electron is 1.6 * 10-19 Coulombs

Conductors & InsulatorsSubstances through which electricity can flow are called Conductors.

Ex: Silver, Copper and Aluminium, etc

Those Substances through which electric charges cannot flow, are called Insulators.

Ex: Glass, Ebonite, Rubber, most plastics, Paper, Dry wood, Cotton, Mica, Bakelite, Porcelain, and Dry Air

What makes Substances Conduct Electricity?

The presence of Free Electrons in a substance makes it a conductor.

The electrons present in insulators are strongly held by the nuclei of their atoms.

So no free electrons in an insulator which can move from one atom to another, an insulator does not allow electric charges to flow through it.

Static Electricity ?

Electric Potential

What happens when a positive charge is placed in the electric field due to another charge?

Electric Potential

Electric potential at a point in an electric field is defined as the work done in moving a unit positive charge from infinity to that point.

Potential Difference

The difference between two points in an electric circuit is defined as the amount of work done in moving a unit charge from one point to the other

point.

Potential difference = Work done / Quantity of Charge moved

Heating Effects of Electric Current

When an electric current is passed through a high resistance wire, like nichrome wire, the resistance

wire becomes very hot and produces heat.

This is called as the Heating effects of Electric current

MAGNETIC EFFECTS OF ELECTRIC CURRENT

Learning ObjectivesMagnetic Field and Magnetic Field LinesMagnetic Field of EarthElectromagnetismMagnetic field patterns produced by current

carrying Conductors of various shapesElectromagnetDifference between Bar Magnet & an

ElectromagnetMagnetism in Human Body

Learning ObjectivesForce on a current carrying conductor placed in a

magnetic fieldKicking Wire ExperimentFleming’s Left Hand RulePrinciple and working of Electric MotorElectromagnetic Induction Fleming’s Right-Hand RuleElectric Generator - AC & DC GeneratorsDomestic Electrical Wiring

Magnetic Effect of Electric Current

“An electric current flowing in a wire produces a magnetic field around it”

Electric Current produces Magnetism

Magnet & Magnetic Field

A magnet is an object which attracts pieces of iron, steel, nickel and cobalt

The space around a magnet in which magnetic force is exerted, is called a

magnetic field

Magnetic Field LinesThe lines drawn in a magnetic field along which a

north magnetic pole would move

The magnetic field lines are also known as magnetic lines of force

The magnetic field lines always begin from the N-pole of magnet and end on the S-pole of the

magnet

DEMONSTRATION ON MAGNETIC FIELD LINES

Properties of Magnetic Field Lines

The magnetic field lines originate from the North pole of a magnet and end at its south pole

The magnetic field lines come closer to one another near the poles of a magnet but they are widely separated at other places

The magnetic field lines do not intersect one another

Magnetic Field of Earth

A freely suspended magnet always points in the north-south direction even in the absence of any other magnetic field.

This suggests that the earth itself behaves as a magnet which causes a freely suspended magnet to point always in a particular direction

The shape of the earths magnetic field resembles that of an bar magnet

The axis of Earth’s Magnetic Field is inclined at an angle of about 150 with the geometrical axis

The Earth’s magnetic Field is due to the Magnetic Effect of Current, which is flowing in the liquid

core at the centre of the earth

Thus, Earth is a huge electromagnet

Why Earth’s Magnetic Field

Questions1. State any two properties of Magnetic Field lines.2. (True/False) The axis of earth’s imaginary magnet and the geographical axis coincide with each other3. Where do the manufacturers use a magnetic strip in the refrigrator? Why is this magnetic strip used?4. Why does a compass needle get deflected when brought near a bar magnet?

http://youtube.com/v/DYLQmSuqPjY

ELECTROMAGNETISM

MAGNETIC EFFECTS OF CURRENT

ELECTROMAGNETISMThe magnetic effect of current was discovered by oersted in 1820Oersted found that a wire carrying a current was able to deflect a

compass needleCompass needle is a tiny magnet which can be deflected only by a

magnetic fieldSince, a current carrying wire was able to deflect a compass

needle, it was concluded that a current flowing in a wire always gives rise to a magnetic field around it

ELECTROMAGNETISMThe importance of magnetic effect of electric current lies in the

fact that it gives rise to mechanical forces

The Electric Motor,Electric Generator,Telephone and Radio

All the above devices utilise the magnetic effects of electric current

The magnetic effects of electric current is also called electromagnetism which means electricity produces magnetism

http://youtube.com/v/p_bU2CInQDE

MAGNETIC FIELD PATTERNS

By current-carrying conductors of various shapes

http://youtube.com/v/Z927bDX1l04

Magnetic Field due to straight current carrying wire

Magnetic Field due to straight current carrying wire

The magnetic field lines around a straight conductor carrying current are concentric circles

whose centres lie on the wire

The magnitude of magnetic field produced by a straight current carrying wire at a given point is:

Directly proportional to the current passing in the wire, and Inversely proportional to the distance of that point from the wire

Important observationsGreater the current in the wire, stronger will be

the magnetic field producedGreater the distance of a point from the wire

current carrying wire, weaker will be the magnetic field produced at that point

As we move away from a current-carrying straight wire, the concentric circles around it representing magnetic field lines, becomes larger and larger indicating the decreasing strength of the magnetic field

Right-Hand Thumb Rule(Maxwell’s Right-Hand Thumb Rule)

Direction of Magnetic Field for a straight current carrying conductor

Imagine that you are holding a current carrying conductor in your right hand so that your thumb points in the direction of current, then the direction in which your fingers encircle the wire will give the direction of magnetic field lines around the wire

Maxwell’s Right-Hand thumb rule is also known as Maxwell’s corkscrew rule

Magnetic Field Pattern due to Circular Loop

(Circular Wire)

Important ObservationsIt has been found that the magnetic effect of current increases if

instead of using a straight wire, the wire is converted into a circular loop

Magnetic field lines are circular near the current carrying loop, as we move away the concentric circles representing magnetic field lines become bigger and bigger

At the centre of the circular loop, the magnetic field lines are straight

At the centre of the circular loop, all the magnetic field lines are in the same direction and aid each other, due to which the strength of magnetic field increases

Important Observations

The magnitude of magnetic field produced by a current-carrying circular loop at its centre is:

Directly proportional to the current passing through the circular loop and

inversely proportional to the radius of circular loop

How to increase the strength of the magnetic field in a circular coil ?

The strength of the magnetic field can be increased by taking a circular coil consisting of a number of turns of

insulated copper wire closely wound together.

If there is a circular coil having n turns, the magnetic field produced by this current-carrying circular wire will be n times as large as that produced by a circular loop of

a single turn of wire.

Important ObservationsThe strength of a magnetic field produced by a circular coil carrying current is directly proportional to both, number of turns (n) and current (I); but inversely proportional to its radius (r).

The Strength of the magnetic field produced by a current-carrying circular coil can be increased:

by increasing the number of turns of wire in the coil,by increasing the current flowing through the coil, andby decreasing the radius of the coil

Clock Face RuleA Current-carrying circular wire behave like a thin disc magnet whose one face is a north pole and the other face is a south pole.

According to Clock face Rule

If the current in the circular wire is in the clockwise direction, then that face of the circualar wire will be South pole

If the current around the face of circular wire flows in the anticlockwise direction, then that face of the circular wire will be North pole

Magnetic Field due to a Solenoid

A solenoid is a coil containing a large number of close turns of insulated

copper wire

Magnetic Field due to a Solenoid

The magnetic Field produced by a current carrying Solenoid is similar to the magnetic field produced

by a bar magnet

Important ObservationsThe lines of the magnetic field pass through the Solenoid and

return to the other endThe magnetic field inside the Solenoid are in the form of parallel

straight linesThis indicates that the strength of the magnetic field is same at all

points inside the solenoidIf the strength of the magnetic field is uniform just same in a

region, it is said to be uniform magnetic fieldThus, magnetic field is uniform inside a currnet carrying Solenoid

Important ObservationsThe strength of the magnetic field produced by a current carrying Solenoid depends on:

The number of turns in the Solenoid. Larger the number of turns in the Solenoid, greater will be the magnetism produced

The strength of current in the Solenoid. Larger the current passed through the Solenoid, stronger will be the magnetic field produced

The nature of core material used in the Solenoid. The use of Soft Iron rod as core in a Solenoid produces the strongest magnetism

ElectromagnetAn electric current can be used for making

temporary magnets known as electromagnets.An electromagnet works on the magnetic effect of

current.

Electromagnet

An Electromagnet is a magnet consisting of a long coil of insulated copper wire wrapped around a soft iron core that is magnetised only when electric current is passed

through the coil

The core of the Electromagnet should be Soft iron because soft iron loses all of its magnetism when current

in the coil is switched off

Bar magnet vs ElectromagnetBar magnet is a permanent

magnetA permanent magnet produces a

comparatively weak force of attraction

The strength of a permanent magnet cannot be changed

The polarity of a permanent magnet is fixed and cannot be changed

An electromagnet is a temporary magnet. Its magnetism is only for the duration of current passing through it

An Electromagnet can produce very strong magnetic force

The strength of the electromagnet can be changed by altering the current

The polarity of an electromagnet can be changed by changing the direction of current in its coil

Permanent magnets are usually made of alloys such as:

Carbon steel, Chromium Steel, Cobalt Steel, Tungsten Steel and Alnico

Alnico is an alloy of aluminium, nickel, cobalt and iron

Permanent Magnets

Magnetic Fields in Human Body

Extremely weak electric currents are produced in the human body by the movement of charged particles called

ions. These are called ionic currents.

These create temporary magnetism in the human body. The magnetism produced in the human body is very very

weak compared to the earth’s magnetic field.

Magnetism in Human Body

The two main organs of the human body where the magnetic field produced is quite significant are the

heart and the brain

This magnetism forms the basis of a technique called Magnetic Resonance Imaging (MRI) which is

used to obtain internal parts of our body.

Force on current carrying conductor placed in a Magnetic

Field

Observations from Oersted’s Experiment

A current-carrying wire exerts a force on a compass needle and deflects it from its usual north-south position

A current-carrying wire exerts a mechanical force on a magnet, and if the magnet is free to move, this force can produce a motion in the magnet

A magnet exerts a mechanical force on a current-carrying wire, and if the wire is free to move, this force can produce a motion in the wire

This can be obtained by applying Newton’s Third Law

Why Force being acted upon a Current carrying wire in a magnetic

field ?

Faraday’s Observation in 1821

When a current-carrying conductor is placed in a magnetic field, a mechanical force is exerted on the

conductor which can make the conductor move

This is the Working Principle of a Motor

http://youtube.com/v/Ue6S8L4On-Y

Important Observations●When a current-carrying conductor is placed in a magnetic field,

a mechanical force is exerted on the conductor which makes it move

●The direction of force acting on a current-carrying conductor placed in a magnetic field is:

i. Perpendicular to the direction of currentii. Perpendicular to the direction of magnetic field

Important point:● Maximum force is exerted on a current-carrying wire only

when it is perpendicular to the direction of magnetic field.

● No force acts on the current-carrying wire when it is parallel to the magnetic field

Important ObservationsThe direction of force on a current-carrying conductor placed in a

magnetic field can be reversed by reversing the direction of current flowing in the conductor

If the direction of current in a conductor and the direction of magnetic field(in which it is

placed), are known, then the direction of force acting on the current-carrying conductor can be found out by using Fleming’s left-hand rule.

Fleming’s Left Hand Rule

Statement

Hold the forefinger, the centre finger and the thumb of your left hand at right angles to one

another. Adjust your hand in such a way that the forefinger

points in the direction of magnetic field and the centre finger points in the direction of current in

the conductor, then the direction in which the thumb points gives the direction of motion of the

conductor

ELECTRIC CURRENT

ALTERNATING CURRENT (AC)DIRECT CURRENT (DC)

Sources of DC & ACDC

BatteriesThermocouplesSolar CellsDynamo

Direct current is also known as Galvanic

CurrentAll the electronic devices

work on Direct Current only

ACAC Generators

All Electrical devices work on AC Supply

We receive AC supply

Alternating Current can be transmitted over long distances without much loss of electrical

energy

ADVANTAGES OF AC OVER DC

The Electric MotorPrinciple, Construction, Working &

Applications

THE ELECTRIC MOTOR

A Motor is a device which converts Electrical energy into Mechanical energy

Principle of a DC Motor

Principle of a MotorAn electric motor utilises the magnetic effect of

current.A motor works on the principle that when a

rectangular coil is placed in a magnetic field and current is passed through it, a force acts on the coil

which rotates it continuously.

When the coil rotates, the shaft attached to it also rotates.

In this way the electrical energy supplied to the motor is converted into the mechanical energy of

rotation

Construction of a DC Motor

Construction of a Motor1. An electric motor consists of a rectangular coil ABCD of insulated copper wire, which is

mounted between the curved poles of a horseshoe type permanent magnet M in such a way that it can rotate freely between the poles N and S on the shaft.

2. The coils AB and CD of the coil are kept perpendicular to thedirection of magnetic field between the poles of the magnet.

3. A device which reverses the direction of current through acircuit is called a commutator (or split ring).

4. The two ends of the coil are soldered permanently to thetwo half rings X and Y of a commutator.

5. A commutator is a copper ring split into two parts X and Y,these two parts are insulated from one another and mountedon the shaft of the motor.

6. The commutator rings are mountedon the shaft of thecoil and they also rotate when the coil rotates

7. The function of commutator rings is to reverse the direction of current flowing through the coil afterevery half rotation of the coil.

8. To pass in electric current to the coil, we use two carbon strips P and Q known as brushes.9. The battery to supply current to the coil is connected to the two carbon brushes P and Q through a switch.10. The function of carbon brushes is to make contact with the rotating rings of the commutator and through them to supply current to the coil.

Construction of a Motor

Working of a DC Motor1.When an electric current is passed into the rectangular coil, this current

produces a magnetic field around the coil.2.The magnetic field of the horseshoe-type magnet then interacts with the

magnetic field of the current-carrying coil and causes the coil to rotate continuously.

APPLICATIONS OF ELECTRIC MOTOR

Every motor has a shaft or spindle which rotates continuously when current is passed into it.(Into

current carrying conductors)Electric Motor is used in:

Electric FansWashing MachinesRefrigeratorsMixer and GrinderElectric Cars & many other applications

Lets Test Our Memory1.What happens when a current-carrying conductor is placed in a

magnetic field?2.When is the force experienced by a current-carrying conductor placed in

a magnetic field largest?3.In the statement of Fleming’s Left Hand Rule, what do the following

represent?i. Direction of centre fingerii. Direction of forefingeriii. Direction of thumb

4. Name the device which converts electrical energy into mechanical energy?5. What is the role of split rings in an electric motor?6. What is the function of commutator in an electric motor?

ELECTROMAGNETIC INDUCTION

Electricity from Magnetism

ELECTROMAGNETIC INDUCTION

The production of Electricity from Magnetism is called Electromagnetic Induction

How?

Notes➢The current produced by moving a straight wire in a magnetic

field is called Induced Current➢The phenomenon of Electromagnetic Induction was discovered

by a British scientist Michael Faraday and an American scientist Joseph Henry independently in the year 1831

➢The process of Electromagnetic Induction led to the construction of generators for producing electricity at power stations

➢A Galvanometer is an instrument which can detect the presence of electric current in a circuit

When an electric current passes through the Galvanometer, then its pointer deflects either to the left side of zero mark or to the right side of the zero mark, depending on the direction of current.

Observations of Faraday & Henry about EMI

➢A current is induced in a coil when it is moved relative to a fixed magnet➢A current is also induced in a fixed coil when it is moved relative to the

fixed coil➢No current is induced in a coil when the coil and magnet both are

stationary relative to one another➢When the direction of motion of coil is reversed, the direction of current

induced in the coil also gets reversed➢The magnitude of current induced in the coil can be increased :

○by winding the coil on a shaft iron core○by increasing the number of turns in the coil○by increasing the strength of magnet, and○by increasing the speed of rotation of coil (or magnet)

Fleming’s Right-Hand Rule

For the direction of Induced Current

Fleming’s Right-Hand Rule

StatementHold the thumb, the forefinger and the centre finger of your right-hand at right angles to one

another.

Adjust your hand in such a way that forefinger points in the direction of magnetic field, and thumb points in the direction of motion of conductor, then the direction in which centre finger points, gives the direction of induced current in the conductor

The electrical generator is a machine for producing electric current or electricity.

This electric generator converts mechanical energy into electrical energy

Example

Electric Generator

Dynamo

Principle of Electric Generator

Electric Generator is an application of EMI

GENERATORS

AC GENERATORDC GENERATOR

The difference between DC & AC Generators is in their construction

http://youtube.com/v/nRMZ3K2pzcE

Domestic Electric CircuitsDomestic Wiring

At the end of Sources of Energy