20 Magnetic Field & Forces

Magnetism S N S N

Extended…

Magnetic Field & Force Analogous to Electric Field–  Moving charge or current creates magnetic field  Magnetic field exerts a force on any other moving charge or current  No magnetic monopole ! Static Charge ~ E-field Moving Charge ~ B-field (any E-field here?)

More Magnetic Fields

Magnetic Field Lines Closed loops Outside N  S Inside S  N Direction & Magnitude (similar to E filed)

Magnetic Field Lines

Micro Picture of Magnet

Magnetic Forces & Right-hand Rule A charged particle with velocity v in magnetic field B, then we have the force on the particle, F: Magnitude Direction Right-hand Rule For current with length l [B] in Tesla: 1 T = 1N/(A.m) B F v +q 

Right-hand Rule: + & -charges

Right-hand Rule: Current & Centripetal Force Field Direction (B) Current Direction (v)

Motion of Charged Particle in B-field

Helical Motion and Auroras No magnetic force on the direction parallel to the B-field.

Magnetic Force on Current More general

Application: Magnetic Rail Gun

Force & Torque on Current Loop

Application: DC Motor

Permeability of vacuum B-field: Long Straight Current

B-field: Current Loops & Solenoids B-field at the center of loop (1 turn) (N turns) (n: turns per unit length)

Force between Parallel Conductor I I’

*Introduction: Biot-Savart Law & Ampere’s Law ll BB r I  B ss

Summary: B-field & Force

Summary: Charged Particle in B- field

Summary: Force on Current- Carrying Conductor

Summary: Force, Torque, & Motor

Summary: B-field Generation

Summary: Current Loop & Solenoids

Summary: B-field Calculation ll BB r I  B ss Biot-Savart Law Ampere’s law

Homework Ch20: 1, 4, 13, 17, 26, 31, 34, 40, 54, 58.

Galvanometer

Right-hand Rule Charged particle/current in B-filed: determine force Force  q(sign). Velocity x B-field Determine B-filed from the current B-field  Current(  l) x Position ( r )

Q2 & Q3

Q7

P31

P34