Lecture #8 Electric dipoles. Dielectrics. Electric Capacitance and Capacitors

Lecture 12. Electrostatic II part


Subject: Physics 1 İnstructor: Ph.D. Khuraman Ahmadova [e-mail]

Lecture #12 Capacitance and Capacitors

Content

• Conductors and insulators. Electric field in medium.

2. Capacitance and Capacitors.

3. Capacitors in Combination

4.Energy Storage in a Capacitor

1. Conductors and insulators. Conductors as Shields

There are three kinds of materials relative to electrical properties:

• Conductors. Conduct electric current. How we have seen from Gauss's law electric field in conductors is equal zero.
• Insulators (dielectrics). They don't conduct electric current. Electric field in dielectrics decreases
• Semiconductors. Conduct electric current but less than conductors.

Conductors as shields.

1. Shielding the inside from the outside. It is well known that no electric fields exist inside a hollow conductor, even if there are charges present outside. The conductor acts like an electrostatic shield.

2. Shielding the outside from the inside.

A charge inside a hollow conductor produces a charge distribution on the outer surface of the conductor, and this induced charge distribution creates an electric field outside the closed conductor. Thus, electrostatic shielding works only in one direction.
However!!!
Shielding the outside can be accomplished by grounding the conductor. This allows charges to flow (from ground) onto the conductor, producing an electric field opposite to that of the charge inside the hollow conductor.
The conductor then acts like an electrostatic shield as a result of the superposition of the two fields.