Sections 1-6 Flashcards
What is the equation for Coulomb’s Law?
F12 = (q1q2)/(4πϵ0)*(r2 − r1)/(|r2 − r1|^3)
What is the value of the permittivity of free space and what are its units?
8.8*10^-12 C^2 N^-1 m^-2
What is the equation for an electric field around a point charge q?
E(r) = q/(4πϵ0)*(1/r^2) (same as coulombs law, but with only one charge rather than two)
What is the equation for the electric dipole moment?
p = qd q = charge d = distance between charges p = moment [Units: Cm]
In what direction does an electric field flow?
From positive to negative.
What are the equations for linear, surface and volume charge density?
Whatever the letter is divided by a change in the value, so dl, dS and dV.
How do you work out the electric field of a dipole?
FInd the contribution from each end of the dipole using the electric field equation and then add them together.
How do you work out the electric flux through a flat surface?
flux = electric field * area of surface * cos(angle)
How do you find the electric flux through an arbitrary surface?
Surface integral of the electric field * the change in area/surface (electric field is constant on surface so can take out of integral).
What is the surface integral of E*dS of a sphere centered on a charge q?
q/ϵ0
What is the main statement in Gauss’s Law?
That the electric flux through the Gaussian surface is the charge enclosed divided by the permittiviy of free space (Qencl/ϵ0)
How do you apply Gauss’s Law?
1 - Look at the symmetry to find out the electric field direction (using appropriate coordinate system)
2 - Pick a Gaussian surface and consider all parts the and electric flux going through each part
3 - Work out the enclosed charge of the Gaussian Surface
4 - Summarise and ensure you have answers for different values of radius
