EM Flashcards
EM range, interactions particles, exchange particles and relative strength, difference to other fundamental forces
Infinite range, all charges, photon, 10^35 strength, controllable
Static
Non-moving point charge like an electron
Coulomb’s law
Experimental, delicate torsional balance than measured forces between two point charges
F= Q1Q2/r squared
Constant of proportionality and consistent
1/4pi epsilon0
Epsilon0 permittivity of a vacuum
4pi= spherical symmertry cylindrical would be 2pi
Normalised unit length vector
n hat = r1-r2 / |r1-r2|
Superposition principle electrostatics
F net = F1 +F2
Functional form of force
F= Q1Q2/ 4pi epsilon0 n hat
Diagram for point charge
Uniform radial electric Field lines in circle outwards arrows pointing out for positive centre
What is q_T
Test charge, positive
Electric field def and equation
Force experienced by test charge
E=F/q
Potential on diagram
Potential is circle
Field lines meaning
Closer together = stronger field
E vector field equation
E= Q/4pi epsilon 0 r squared x r hat
What happens as r tends to 0 for V and E
For E divergence reveals position
V tends to infinity breaks down
Potential equation
V(r)= Q/ 4pi epsilon0 r
Potential def
Point on radius that experiences same force, line of constant potential
E V relation
E= - grad V where grad is partial derivative x,y,z vector
Point charge
Finite amount of charge Q sitting at a point (occupies infinitesimal volume)
Charge density for point charge
Roe= Q/volume tends to infinity
Negative point charge
Field lines change direction q_T would be attracted
Continuous charge
Roe can relate to E, density
Discrete charge distribution method
Add x and y separately use triangles total energy = sum of separate energies accounting for direction
Or use total V and grad to find E
Charge density long line of charge
Lambda= Q/L
Continuous charge distribution
