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

2020
Views:

310

Pages:

8
Author:

esfredint7qo

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 Parallel-plate Capacitor • Electric Field for “infinite” sheet of charge: Area A d  E 2 0 Which of the following statements about a parallel plate capacitor is false? 1) The two plates have equal charges of the same sign. 2) The capacitor stores charges on the plates. 3) The capacitance is proportional to the area of the plates. 4) The capacitance is inversely proportional to the separation between the plates. 5) A charged capacitor stores energy. Parallel-plate Capacitor • With “nothing” (air) in the gap, C 0 A d Figure 24.17b 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 If a dielectric is inserted between the plates of a parallel-plate capacitor that is connected to a 100-V battery, the 1) 2) 3) 4) 5) voltage across the capacitor decreases. electric field between the plates decreases. charge on the capacitor plates increases. Both 2 and 3. None of the above. Energy stored in a capacitor 2 Q 2 1 U  2 CV 2C Energy is stored “in the electric field”. Energy density: U 2 1 u  2 0E Volume

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