HW1 return! FERPA-approved military fashion!

Equipotential and field lines: Equipotential lines field lines:

Equipotential lines and the Electric field: Quantitative relation

? Equipotential lines and the Electric field: Quantitative relation

Equipotential lines and the Electric field: Quantitative relation

Small enough scale, looks like parallel plate field: In direction of

Small enough scale, looks like parallel plate field: (calculate) In direction of

Formally: Direction: downhill

Pretending that V(x) is like a topographic map: A)The Electric field always points in the direction of steepest descent! B) The magnitude of the electric field is given by the slope in that direction! alternate units for E : V/m

Estimating Electric field strength:

Something Unrelated ….

Example where’s V = 0? 5 cm Two possibilities!

Example where’s V = 0? 5 cm x Possibility #1

Example where’s V = 0? x Possibility #2

Conductors!

Electric fields just outside of a conductor are strong where the conductor is pointy: Dielectric strength of a material = maximum electric field the Material can stand before breaking down. Dielectric strength of air = 3 × 10 6 V/m Example: Voltage of a 15 cm spark!

Capacitance:

Must be at different potentials!

Capacitance:

Parallel-plate capacitor: 10 cm 0.1 cm Square plates 10 cm

Parallel-plate capacitor: Q = ?

Parallel-plate capacitor: Dielectric constant! 0.1 cm 10 cm Dielectric! Square plates Quartz:  = 4.3

Leyden-jar demo V de G demo again, big and little spheres – spark size