Setlist L14 (90 minutes)

Electric field configurations Prep: Electric Field Worksheet. Noah’s Simulation, Rod, plane, ball

1. Last Class: Intermolecular forces, the field of a point charge 2. Ion-Dipole interactions and Dipole-Dipole Interactions 3. Worksheet [Q4] - Electric field from an electric dipole 4. Worksheet [Q5] - Putting charges close together is like taking a derivative 5. van der Walls and dispersion forces. This is for homework! 6. Clicker [Q] - force between a dipole and a charge - D 7. Clicker [Q] - rotation of dipole - E 8. Torque on a dipole 9. Continuous Charge distributions 10. Clicker [Q] - Direction of a field from infinite plane - C 11. Clicker [Q] - Strength of a field from an infinite plane - C 12. Worksheet [Q] - Potential energy and electric potential in plane of charge 13. Discussion of how if the system doesn’t change, the physics can’t change

(symmetry arguments) 14. Show them the standard field configurations. Point out that the plane depend on

nothing, the line depends on 1/r, and the sphere depends on 1/r2. This is not a coincidence.

15. Clicker [Q] - Unevenly charged plates. - C 16. Electric field = 0 in a conductor: A consequence of the ability for charge to move

freely.

x

The line of chargeField D

moist dran

linear charge ddensity d I d

i infinite sex dqi Adx

ttttttttttttttttttttt.aeThe electric field is the sum of allthe contributions from the point chosesdqi

Etat Ec

All the x components cancel so it'sonly y that contributes

Etat Ey i

E Ei Sinaiif

Stalag sinaI

Now we knew that

dq ddxri idf

sin D i d dri TE

Our earlier equation becomes

Etat S IxE TAY FI

E

kids d

which is some trig substitution integral

Etata yjh

We see for an infinity long wireL s we get

Etat kidWhich is the commonly used formulafor a line of charge

of E K

rti

It's pretty tedious to set which iswhy we'll use other methods

x