ELECTRODYNAMICS. Electrodynamics: The Study of Electromagnetic Interactions. Magnetism is caused by charge in motion. Charges at rest have just an electric field But, when they move, they generate both an electric field and a magnetic field
First Right Hand Rule: thumb points in direction of current, fingers curl in direction of magnetic field- note compass readings. Use for current-carrying wire.
Fig 19.15b, p.678
For loop or coil of wire, can still use 1st RHR, but direction of current constantly changes.
Easier to use 2nd Right Hand Rule. Fingers curl in direction of current, thumb points to direction of magnetic field.
N is the NUMBER of loops
A solenoid is a helix, so it behaves differently than stacked loops. The major factor for the magnetic field produced by a solenoid is the turn spacing.
n is the turn density, the number of turns per unit length (n = N/L)
At the ends of the solenoid, about half the field “leaks out”.
No rotation when loop is perpendicular to B-field.
The DC motor is simple, yet very important application.
Currents in Same Direction…
Currents in Opposite Directions…