Lecture 7 Capacitors

Micro-economists are wrong about specific things, and macroeconomists are wrong about things in general. Yoram Bauman

The potential at 1 is V=0 V=+400 V 1 2 1mm 3mm 1.Greater than at 2 2.Less than at 2 3.The same as 2

The potential at point 2 is V V 4.300V 5.400V 6.None of the above

The electric field strength at 1 1.Is greater than at 2 2.The same as at 2 3.Is less than at 2 4.Cannot tell from diagram

The electric field strength at 2 is 1.0 v/m v/m v/m v/m 5.Need more information

QUIZ #3 A proton has been accelerated through a potential difference of -1000V. What is its speed?

Electric Field from Potential Finding E from ΔV: Direction perpendicular to equipotential surfaces and from higher to lower potential

Capacitors Can store electric charge Two conductors, one with +Q, the other with -Q and voltage difference ΔV Capacitance defined by Units C/V = 1 Farad = 1F

Plane Parallel Plate Capacitor Recall E between plates is Special case of plane parallel plate capacitor If d = 1mm, what is A? If square plates, what is L? A=L 2

Put dielectric spacer between plates Dielectric = insulator is the dielectric constant. See table 21.2 page 709 How would you make C large while keeping physical size of capacitor small?

Energy stored in capacitor U is the energy stored, book uses U C Energy stored in demonstration capacitor?