1/25/2008 J.Velkovska 1 PHYS117B: Lecture 8 More about electric potential  Equipotential lines  Relation between E and V Capacitance

1/25/2008 J.Velkovska 2 Electric field lines

1/25/2008 J.Velkovska 3 Electric potential of a point charge Potential is = 0 at infinity E goes as 1/r 2 … V ~ 1/r ( last lecture we integrated E to find V)

1/25/2008 J.Velkovska 4 Electric field and potential

1/25/2008 J.Velkovska 5 Topographic Maps and …pictures

1/25/2008 J.Velkovska 6 In Electrostatics, the peaks and valleys are created by charged objects Density of lines indicates strength of E

1/25/2008 J.Velkovska 7 Electric potential inside a || plate capacitor Uniform field => Equipotential lines are equally spaced

1/25/2008 J.Velkovska 8 More complex cases

1/25/2008 J.Velkovska 9 Calculating E from equipotential map

1/25/2008 J.Velkovska 10 Calculating E from V

1/25/2008 J.Velkovska 11 Capacitors and capacitance Two conductors separated by an insulator or vacuum charged to +Q and –Q form a capacitor. Net charge on the capacitor is 0 Once the charge is established: potential difference between the two conductors Potential difference means – you can store energy on the capacitor Capacitance: measures the ability of the capacitor to store energy

1/25/2008 J.Velkovska 12 Capacitors can have any shape

1/25/2008 J.Velkovska 13 Capacitance depends on shape of the conductors and the medium

1/25/2008 J.Velkovska 14 When we put a dielectric between the plates: E –weaker, V – smaller, C - larger

1/25/2008 J.Velkovska 15 Capacitors in series

1/25/2008 J.Velkovska 16 Capacitors in parallel