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

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

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

4. Magnetic attraction/repulsion
Disc 19, #1

5. 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

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

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

8. 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

9. Right hand rule
Disc 19 #7
Disc 19 #9

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

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

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

13. Example #1
Force on a current

14. 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

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

16. Example #2
Force on a charge

17. 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

18. 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

19. 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

20. Coils with magnet
Disc 20, #12