WHAT IS A MAGNETIC FIELD? 

WHERE IS THE MAGNETIC FIELD STRONGEST AT? 

LINE OF FORCE

THE EARTH'S MAGNETISM

Circulation of currents in molten iron at the core

It drifts gradually 

currently the north magnetic pole is in northern canada

Tectonic plates

magnetic field can reverse suddenly

WHERE IS THE FORCE EXPERIENCED? 

Current carrying wire placed at an angle to the lines of force experience a force due to field

If it's paralell the force is zero 

If it's perpendicular, force is maximum

MOTOR EFFECT

Force perpendicular to wire and line of force

Tested using wire placed between opposite poles of a U shaped magnet so at right angles to line of force and magnetic field

FLEMING'S LEFT HAND RULE*

MAGNETIC FLUX DENSITY

Strength of magnetic field

Force per unit length per unit current on a current carrying conductor at right angles to the magnetic field lines

F = BiL Gives magnitude (only applies at right angles)

Flemings left hand rule gives direction

THE COUPLE ON A COIL IN A MAGNETIC FIELD*

ELECTRON BEAMS

Controlled by magnetic fields

Changing current in the coil that controls this will change the strength of the field causing the electrons to change direction

DEFLECTION

Stronger the force, stronger the deflection of the beam of electron. each electron feels a force due to the magnetic field

Beam follows circular path because direction of force on each electron is perpendicular to the direction of motion of the electron

WHY DOES A CURRENT CARRYING WIRE IN A MAGNETIC FIELD EXPERIENCE A FORCE? 

HIGH ENERGY COLLISIONS

Magnetic fields measure momentum, seperate different charged particles.

Positive particles are deflected to opposite sides to the negative ones

THE ELECTRIC MOTOR

Coil of insulated wire that spins between poles of a U magnet

Wires at opposite ends of coil are acted on forces in opposite direction

Force on each edge makes coil spin around axis WHEN CURRENT PASSES AROUND COIL