Electromagnetism Forces in nature: How does matter interact? Four Fundamental Forces: Long range: Gravity Mid Range: Electromagnetic Short Range: Strong and Weak

Electric Charge (~Mass) Two types of electric charge: positive and negative Unit of charge is the coulomb [C] Charge of electron (negative) or proton (positive)is Charge is quantized Charge is conserved

Electric Force (~Gravity) The electric force between charges q 1 and q 2 is (a)repulsive if charges have same signs (b) attractive if charges have opposite signs Like charges repel and opposites attract !!

Coulomb's Law Coulomb’s law: Force by q 1 on q 2 Direction: along the line joining the two charges Repulsive or attractive Coulomb’s constant in vacuum:

The superposition principle If many charges are present: Net force is on any charge is the vector sum of the forces from all the individual charges In general:

The electric field The electric field at a point is the force acting on a test charge q at that point divided by the charge q For a test charge q has the direction and sense of the force on a positive charge.

Electric field created by a point charge Q is outwards a positive charge and inwards a negative charce

The superposition principle for fields The electric field due to a collection of N point charges is the vector sum of the individual electric fields due to each charge:

Example of vector field: gravitation

Comparison with gravity

Electric field lines

( particleSource/02-ParticleSource_320.html) Flows With Sources

( particleSink/01-ParticleSink_320.html) Flows with sinks

( particleCirculate/03-PartCircMotion_320.html) Circulating flows