Physics Department, New York City College of Technology Magnetism Physics Department, New York City College of Technology

Key words Magnetism Magnetic field North pole South pole Right hand rule Magnetic force Solenoid

Magnets North pole, Sourth pole A magnet can exert force on another one They interact through the magnetic field

Magnetic attraction/repulsion Disc 19, #1

Magnetic fields A magnetic field surrounds a magnet The unit is Tesla (T) Magnetic field lines Direction:tangent to a field line Strength:proportional to the number of lines per unit area

Magnetic fields around bar magnets Disc 19, #4 Disc 19, #5

The Earth as a magnet Geographic poles Magnetic poles Why a compass points to the North Declination

Electric currents produce magnetic fields Right-hand rule grasp the wire with the right hand so the thumb points in the direction of the current fingers will encircle the wire in the direction of the magnetic field

Right hand rule Disc 19 #7 Disc 19 #9

Magnetic force on a current A current carrying wire experiences a force in a magnetic field The magnitude is

Magnetic force on a current (continued) Right-hand rule Direction: Perpendicular to direction of the current direction of the magnetic field

The definition of magnetic field When  = 90, then The magnetic field can be defined using The SI unit for B is tesla (T)

Example #1 Force on a current

Force on electric charge moving in a magnetic field The magnitude is v is the velocity B is magnetic field  is the angle between and Direction: right-hand rule

Deflected electron beam Disc 20, #3 Disc 20, #4

Example #2 Force on a charge

Magnetic field due to a long straight wire The magnitude is I is current r is the distance from the wire 0 is permeability of free space Direction: right-hand rule I

Force between two parallel wires Magnitude: I1 and I2 are currents d is the separation l is the length of the wire Direction: attractive between currents in the same direction repulsive between currents in the opposite directions

Solenoid The magnetic field within a solenoid is I is current N is the number of turns l is the length of the solenoid 0 is permeability of free space

Coils with magnet Disc 20, #12