mag fields

7.5 Magnetic Fields

What happens when a current in a wire passes through a wire

a magnetic field it induced
- field lines form cocentric rings

magnetic flux density

one Tesla = a force of 1N on 1m of wire carrying a current of 1A perpendicular to the magnetic fields

force exerted on a current carrying wire when placed in a magnetic field

F=BIL

direction of magnetic field lines

north to south

direction of force acting on current carrying wire in a magnetic field

perpendicular to current

how to derive F=BQv

force F=BL
current I=Q/t
charged particle moving distance L has velocity v=L/t
F=BQv

what path do charged particles follow when in a magnetic field

force is always perp. to direction so force acts as centripetal force, so as F=BQv and F=(mv²)/r , r=(mv)/(BQ)

what happens if the mass of a charged particle increases?

the radius of its path increases

cyclotron

• charged particles fired into an electrode, where the mag. field causes it to take a circular path and leave the electrode

• an applied p.d. between electrodes accel. particles across gap

  • as speec increases, radius increases

• p.d. is reversed so particle accel. across again

magnetic flux, Φ

number of field lines passing through an area

equation for magnetic flux

Φ=BA

magnetic flux linkage

NΦ = BAN where N=no. turns on coil

if magnetic field is not perpendicular to field

NΦ = BANcosθ where θ is the angle between the magnetic field and the normal of the coil to the plane