Lecture 17Capacitance:

Computer Key Button – Estimate Capacitance:

Please verify.

Energy stored in a capacitor, Q, A, DRevisit:

Fig(clicker) 17-1

Fig(clicker) 17-1 cont.

When there is E there is electric energy

Dielectric Mediums

Examples of κκ

Vacuum 1Air 1.0006Plastic 5Water 80Semi-conductor 300Conductor infinity

Microscopic Picture:

For fixed plate charge Q

Dielectric Mediums continued...

2 limits:

General κ and Q fixed:

Fig(clicker) 17.2

Fig(clicker) 17.3

Hint on HW17-3 : 005

Hint:

Where charges are all at the surface of the three shells

Preview of Ch. 18: Magnetic Field due to a long wire