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?

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? Iron steel cobalt nickel 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 looses its magnetism (Temporary ) Steel retains its Magnetism (permanent)

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

Induced magnetism

Making magnets Single touch method The end where the stroking pole leaves the bar becomes the opposite pole.

Making magnets Double 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 demagnetization 2. 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 pole If it is clockwise then that is the South pole 2.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 current in a long straight wire,

Magnetic flux pattern due to a current in a short circular coil of wire. Magnetic effect of an electric current Use the right hand grip rule

Magnetic effect of an electric current Magnetic flux pattern due to a current in a solenoid. Grip the solenoid with the right hand with the fingers in the direction of the current The 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… Go back and review….. remember… u can not sleep if u don’t know it. sweet dreams