electromagnetism
DESCRIPTION
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] - PowerPoint PPT PresentationTRANSCRIPT
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
,e C10602.1 19e
Charge is quantized
NeQ Charge is conserved
, epn ee
Electric Force (~Gravity)The electric force between charges q1 and q2 is
(a) repulsive if charges have same signs
(b) attractive if charges have opposite signs
Like charges repel and opposites attract !!
Coulomb's LawCoulomb’s law:Force by q1 on q2
Direction: along the line joining the two chargesRepulsive or attractive
221
r
qqkF e
Coulomb’s constant in vacuum:
229
0
C/Nm1094
1
ek
The superposition principleIf many charges are present:Net force is on any charge is the
vector sum of the forces from all the individual charges
In general:
23133 FFF
N
iijNjjjj FFFFF
121 ...
The electric fieldThe 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
q
FE
EqF
has the direction and sense of the force on a positive charge.
E
Electric field created by a point charge Q
2
1
r
Qqk
FE e
2r
QkE e
is outwards a positive charge and inwards a negative charce
E
E
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:
N
iiN EEEEE
121 ...
Example of vector field: gravitation
Comparison with gravity
Electric field lines
(http://ocw.mit.edu/ans7870/8/8.02T/f04/visualizations/vectorfields/02-particleSource/02-ParticleSource_320.html)
Flows With Sources
(http://ocw.mit.edu/ans7870/8/8.02T/f04/visualizations/vectorfields/01-particleSink/01-ParticleSink_320.html)
Flows with sinks
(http://ocw.mit.edu/ans7870/8/8.02T/f04/visualizations/vectorfields/03-particleCirculate/03-PartCircMotion_320.html)
Circulating flows
