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

2. 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

3. 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 !!

4. 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:

5. 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:

6. 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.

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

8. 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:

9. Example of vector field: gravitation

10. Comparison with gravity

11. Electric field lines

13. (http://ocw.mit.edu/ans7870/8/8.02T/f04/visualizations/vectorfields/02- particleSource/02-ParticleSource_320.html) Flows With Sources

14. (http://ocw.mit.edu/ans7870/8/8.02T/f04/visualizations/vectorfields/01- particleSink/01-ParticleSink_320.html) Flows with sinks

15. (http://ocw.mit.edu/ans7870/8/8.02T/f04/visualizations/vectorfields/03- particleCirculate/03-PartCircMotion_320.html) Circulating flows