The earth is a giant magnet Magnetic field lines of force leave the north pole and enter the south pole. What is a magnetic field?

The earth is a giant magnetMagnetic field lines of force leave the north pole and enterthe south pole. What is a magnetic field?

Magnetic field

The space around a magnet where the forces of attraction and repulsion act is the magnetic field. A magnetic

field is made up of lines of force.

What are poles?

The poles represent the part of a magnetic field where the magnetic forces appear to be concentrated.

Magnetic flux patterns

Magnetic flux patterns

Magnetic?

Iron steel

cobaltnickel

These materials along with certain other alloys are

called ferromagnetic materials.

Hard or soft material?

Iron has stronger induced magnetism.

Steel has a weaker induced magnetism.

Hard or soft?

Iron

loos

es it

s mag

netis

m

(Tem

pora

ry)

Steel retains its

Magnetism (perm

anent)

Hard or soft?

Iron is a magnetically soft material. Strong but temporary!Steel is a magnetically hard material. Weak but permanent!

Induced magnetism

Making magnetsSingle touch method

The end where the stroking pole leaves the bar becomes the opposite pole.

Making magnetsDouble touch method

The end where the stroking pole leaves the bar becomes the opposite pole.

Making magnets: can a magnet have similar poles at its ends?

Consequent poles

The end where the stroking pole leaves the bar becomes the opposite pole.

The Domain Theory of magnets

Magnetic material In demagnetized condition

Magnetic material In magnetized condition

Dipoles in magnetic domains

Domain theory explains:1.Demagnetization: mechanical vibrations can

cause demagnetization2. Magnetic saturation: strength of a magnet

cannot be increased beyond a certain limit.3. Breaking a magnet: breaking a magnet the broken ends maintain the poles.

Magnetic keepers

Magnetic effect of current

electromagnet

To tell the poles: 1. face the coil, trace the direction of current flow, if it is anticlockwise then that is the North poleIf it is clockwise then that is the South pole2.Use right hand grip rule, the thumb points to the N, the end is the S

Direction of the magnetic field

The right hand grip rule

Grip the wire with your right hand, the field lines will go in the direction of the fingers.

Magnetic effect of an electric current

Magnetic flux pattern due to a currentin a long straight wire,

Magnetic flux pattern due to a currentin a short circular coil of wire.

Magnetic effect of an electric current

Use the right hand grip rule

Magnetic effect of an electric currentMagnetic flux pattern due to a current in a solenoid.Grip the solenoid

with the right handwith the fingers in the directionof the currentThe thumb points to the north pole

Direction of the magnetic field

The right hand grip rule

Grip the wire with your right hand, the field lines will go in the direction of the fingers.

Kicking wire experiment

Force on conductor

Field due to permanent

magnet

Field due to current in wire

Two fields interact to produce

force (motion)

Fleming’s left hand rule

Used to determine direction of motion of conductor

d.c. electric motor

Fields interact, coil turns

END OF MOTORS…

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u can not sleep if u don’t know it.

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