University:
Amherst College
Course:
PHYS 117 | Introductory Physics II: Electromagnetism and Optics
Academic year:

2020
Views:

338

Pages:

9
Author:

socalhapaguy4ma

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 on the surface. Spherical conductor in Equilibrium • Potential inside the conductor is a constant: kQ Vin  R • Potential of conductor is proportional to charge on it. 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: Q  CV – Constant of proportionality C is called capacitance. – Capacitance is a geometric and materials property. – Units: Farad = Coulomb/Volt 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: Area A d  E 2 0 Parallel-plate Capacitor • With “nothing” (air) in the gap, C 0 A d • The capacitance changes when a dielectric (insulator) is placed in the gap. Figure 24.17b Figure 24.17c Parallel-plate Capacitor • With “nothing” (air) in the gap, C 0 A d • The capacitance when a dielectric (insulator) is placed in the gap is C   0 A d

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