Conductors in Equilibrium E = 0 inside the conductor. E at the - - PowerPoint PPT Presentation

Conductors in Equilibrium

• E = 0 inside the conductor.

– E at the surface is perpendicular to the surface. – Potential inside conductor is a constant.

• Excess charge on the conductor must reside
• n the surface.

Spherical conductor in Equilibrium

• Potential inside the conductor is a constant:
• Potential of conductor is proportional to

charge on it.

in

kQ V R 

Capacitor

• Two (or more) conductors at different

potentials form a capacitor.

• A capacitor “stores” charge and energy.
• Capacitance:

– Charge “moved” from one conductor to the other is proportional to the potential difference between the conductors: – Constant of proportionality C is called capacitance. – Capacitance is a geometric and materials property. – Units: Farad = Coulomb/Volt

Q C V  

As the voltage in the circuit is increased, the capacitance

1) increases. 2) decreases. 3) does not change.

Parallel-plate Capacitor

• Electric Field for “infinite” sheet of charge:

d Area A

2 E   

• With “nothing” (air) in the gap,
• The capacitance changes when a dielectric

(insulator) is placed in the gap.

Parallel-plate Capacitor

0A

C d  

Figure 24.17b

Figure 24.17c

• With “nothing” (air) in the gap,
• The capacitance when a dielectric (insulator)

is placed in the gap is

Parallel-plate Capacitor

0A

C d  

0A

C d  