1. ELECTROMAGNETISM

2. WHAT IS ELECTROMAGNETISM?
ELECTROMAGNETISM IS NOTHING BUT A MAGNETIC FIELD PRODUCED BY AN ELECTRIC CURRENT.
HANS OERSTED OBSERVED IN HIS EXPERIMENTS THAT
WHEN A CURRENT IS PASSED THROUGH A CONDUCTING WIRE, A MAGNETIC FIELD IS PRODUCED AROUND IT.

3. WHAT HAPPENS IN A STRAIGHT CONDUCTOR THROUGH WHICH CURRENT IS PASSED
WHAT HAPPENS IN A STRAIGHT CONDUCTOR THROUGH WHICH CURRENT IS PASSED? HOW IS THE MAGNETIC FIELD FORMED?
ONE OF THE RULES BY WHICH THE DIRECTION OF MAGNETIC FIELD IN A STRAIGHT CONDUCTOR IS GIVEN BY FLEMING’S RIGHT HAND THUMB RULE.
IT STATES THAT IF WE HOLD A CURRENT CARRYING CONDUCTOR IN RIGHT HAND SUCH THAT THE THUMB POINTS IN THE DIRECTION OF CURRENT, THEN THE DIRECTION OF FINGERS ENCIRCLING THE CONDUCTOR GIVES THE DIRECTION OF MAGNETIC LINES OF FORCE AROUND IT.

4. MAGNETIC FIELD DUE TO CURRENT IN A LOOP
THE MAGNETIC LINES BECOME DENSER IF
THE STRENGTH OF CURRENT IS INCREASED
THE NUMBER OF TURNS IN THE LOOP ARE INCREASED

5. SOLENOID WHAT IS A SOLENOID?
IT IS AN INSULATED COPPER WIRE WOUND OVER A PLASTIC TUBE WHICH BEHAVES LIKE A MAGNET WHEN CURRENT IS PASSED THROUGH IT.

6. CURRENT CARRYING CONDUCTOR IN A MAGNETIC FIELD
The force F α current I
The force F α strength of magnetic field
The force F α length of the conductor
when no current flows in the conductor, no force acts on the conductor and there is no movement
when current is passed through the conductor, a force acts on the conductor.
on reversing the direction of current, the force acts in the opposite direction.

7. D.C. MOTOR
BEFORE WE GO INTO THE WORKING OF D.C.MOTOR, WE SHOULD KNOW FLEMING’S LEFT HAND RULE.
WHY SHOULD WE KNOW?
ONLY THEN WE CAN FIND WHICH DIRECTION THE CONDUCTOR MOVES UP

8. PARTS OF A D.C.MOTOR CORE: Soft iron laminated cylinder
COIL : Insulated copper wire of many turns
COMMUTATOR: Reverses the direction of the coil every half turn.
BRUSHES: To supply a continuous current to the coil through the commutator
ELECTRO MAGNET: To provide a strong uniform magnetic field
A D.C.SOURCE (BATTERY): To provide current to the coil

9. PRINCIPLE OF A D.C.MOTOR REFER TO THIS LINK WHILE READING THIS NOTES
REFER TO THIS LINK WHILE READING THIS NOTES
PRINCIPLE OF DC MOTOR: WHEN AN ELECTRIC CURRENT IS PASSED THROUGH A CONDUCTOR PLACED NORMALLY IN A MAGNETIC FIELD, A FORCE ACTS ON THE CONDUCTOR WHICH MAKES IT TO MOVE. THE DIRECTION IS GIVEN BY FLEMING’S LEFT HAND RULE

10. WORKING OF A D.C.MOTOR
THE PLANE ABCD IS HORIZONTAL AND SPLIT RING S1 TOUCHES BRUSH B1, SPLIT RING S2 TOUCHES BRUSH B2
CURRENT FLOWS IN DIRECTION ABCD
CURRENT IN ARMS AB AND CD IS PERPENDICULAR TO THE MAGNETIC FIELD. SO EACH ARM EXPERIENCES A FORCE WHICH PRODUCES A COUPLE
AS PER FLEMING’S LEFT HAND RULE, AB MOVES DOWNWARDS, AND CD MOVES UPWARDS. (VERY IMPORTANT)
COIL CD MOVES UPWARDS,
90 DEGREES PERPENDICULAR TO THE PLANE OF PAPER. SO NO CONTACT BETWEEN BRUSH AND SPLIT RING. SO CURRENT FLOWS
180 DEGREES ---- ROTATES DUE TO MOMENTUM. SO SPLIT RING S1 TOUCHES BRUSH B2, SPLIT RING S2 TOUCHES BRUSH B1. NOW FORCE IS MAXIMUM WHEN THE COIL TURNS 180 DEGREES
270 DEGREES ---- AGAIN NO CONTACT LIKE IN 90 DEGREES. BUT DUE TO MOMENTUM IT ROTATES
360 DEGREES ---- CONTINUES TO MOVE IN THE CLOCKWISE DIRECTION

11. ELECTROMAGNETIC INDUCTION
IF A MAGNETIC FIELD IS PRODUCED BY AN ELECTRIC CURRENT, THEN IT SHOULD BE POSSIBLE TO PRODUCE AN ELECTRIC CURRENT BY THE MAGNETIC FIELD.
WHEN THERE IS A CHANGE IN THE NUMBER OF MAGNETIC FIELD LINES LINKED WITH THE CONDUCTOR, AN EMF IS DEVELOPED BETWEEN THE ENDS OF THE CONDUCTOR. THIS CONTINUES TILL THE CHANGE IS HAPPENING. THIS PHENOMENON IS CALLED ELECTROMAGNETIC INDUCTION.
To explain in a more simple manner, electric current can be produced in a wire by simply moving a magnet in or out of a coiled part of wire. Voltage is induced only as long there is relative motion between the coil and the magnet.

12. MUTUAL INDUCTION
WHEN AN ALTERNATING CURRENT IS PASSED IN THE PRIMARY COIL,WOUND ON A SOFT IRON CORE, AN INDUCED EMF IS PRODUCED IN THE SECONDARY COIL, WOUND ON A SOFT IRON CORE.
Do you see that one coil is connected to a AC source and the other coil connected to a galvanometer?
We call the first coil(connected to power) as primary coil. And the second coil( connected to galvanometer) as secondary coil.
When switch is ON in the primary, current flows in the primary coil and a magnetic field is created. When the
switch is continuously switched ON and OFF, a varying magnetic field is created in the secondary coil due to induction. This creates a voltage in the secondary coil.

13. PRINCIPLE OF A TRANSFORMER
TRANSFORMERS WORK ON THE PRINCIPLE OF MUTUAL INDUCTION.
TRANSFORMER IS A DEVICE WHERE THE AMPLITUDE OF AN ALTERNATING EMF CAN BE EITHER INCREASED OR DECREASED.
HOWEVER THE FREQUENCY IS UNCHANGED (50 Hz)
TRANSFORMERS
STEP UP TRANSFORMERS STEP DOWN TRANSFORMERS
To change from low to high to change from high voltage to low voltage
voltage
Number of turns of sec. coil Number of turns of primary coil is more
is more compared to primary compared to primary

14. Construction of a transformer
TURNS RATIO: NUMBER OF TURNS IN SECONDARY COIL
NUMBER OF TURNS IN PRIMARY COIL
IF THIS RATIO> 1, THEN IT IS A STEP UP TRNASFORMER
IF THIS RATIO< 1, THEN IT IS A STEP DOWN TRNASFORMER

15. A.C. GENERATOR CONSTRUCTION OF GENERATOR
IT CONVERTS MECHANICAL ENERGY TO ELECTRICAL ENERGY USING THE PRINCIPLE OF ELECTROMAGNETIC INDUCTION
PRINCIPLE : A COIL IS ROTATED IN A MAGNETIC FIELD. WHEN IT IS ROTATING, THE COIL CUTS THE MAGNETIC FIELD. THIS INDUCES AN EMF. THUS A GENERATOR ACTS AS A SOURCE OF CURRENT.
CONSTRUCTION OF GENERATOR

16. Working of an ac. Generator:
PARTS OF A GENERATOR
FIELD MAGNET: IT PRODUCES A RADIAL MAGNETIC FIELD
ARMATURE : IT IS A SOFT IRON CORE ON WHICH A COIL ABCD
HAVING A LARGE NUMBER OF TURNS OF INSULATED
COPPER WIRE
SLIP RINGS :TWO COAXIAL METALLIC RINGS WHICH ROTATE WITH
THE COIL
BRUSHES : MADE OF CARBON. DO NOT ROTATE WITH THE COIL
AND SLIP RINGS
Working of an ac. Generator:
See this link:

17. EXPLANATION OF WORKING OF AN AC GENERATOR
BASICS TO REMEMBER
Let the plane of coil be perpendicular to magnetic field. Maximum magnetic lines are cut.
As the coil rotates, fewer lines are cut.
when the plane of coil is parallel, no lines are cut
At 0 degrees: Coil is rotated clockwise. Magnetic flux decreases and therefore emf is induced and a current is produced.
90 degrees coil rotation: plane of coil becomes parallel. No magnetic lines are cut. Magnetic flux linked with the coil is zero. Emf induced is maximum because rate of change of magnetic flux is maximum.
180 degrees coil rotation: coil again becomes normal(perpendicular). Magnetic lines passing through the coil becomes maximum. Rate of change of magnetic flux is zero. No emf is induced in the coil.
270 degrees coil rotation: magnetic flux linked with the coil decreases and emf again increases to maximum value, but in opposite direction.
360 degrees coil rotation: induced emf reduces to zero. And magnetic flux linked with the coil becomes maximum.

18. THANK YOU FOR
YOUR PATIENCE