Capacitors & Dielectrics 03 Energy Stored in Capacictors 

OPENING QUESTIONS: Contrast electrical potential with electrical potential energy. OBJECTIVE: 1) I will be able to derive an expression for the capacitance of a parallel plate capacitor after today's class 2) I will be able to calculate the energy stored in a capacitor after today's class 3) I will be able to derive an expression for the energy density in a capacitor after today's class WORDS/FORMULAE FOR TODAY TERMS:
CONSTANTS:
UNITS:
FORMULAE:
CALENDAR: Quiz on Thursday WORK O' THE DAY  ════════════════════ I need to emphasize something from the chapter yesterday: How to evaluate charge on a capacitor:
════════════════════ ENERGY OF A PARALLEL PLATE CAPACITOR Let's again briefly review a capacitor present in an electronic circuit: Notice in this situation that the chemical energy stored in the battery is transformed into electrical potential energy stored in the capacitor. If we graph the change in electrical potential vs charge stored in the plates of a capacitor we get a straight line: Notice also that the slope of the line is also of interest: 1/C Through just a bit of integration (found on page 787 but I'm not going to require that you memorize or practice that) we can find that the Work done to move a charge through that potential difference is: Q^{2}/2C ════════════════════ Recall the relationship between electric potential energy, charge and electric potential: U = Q∆V From this relationship we can find the area under the 'curve'. The 'curve' here is a triangle so the area of that triangle is given as 1/2Bh or: U_{E}=1/2Q∆V
And since UE = W we can also add from above: U_{E}= Q^{2}/2C = 1/2Q∆V = 1/2 C(∆V)^{2} (I dunno about you, but methinks that is DEFINITELY FLASH CARD TIME!) ════════════════════ Please work through Example 26.3 (I forgot to have you do that yesterday) and 26.4 ════════════════════
HOMEWORK: HW Problems Conceptual 26.7 (yes, we know that capacitors do store enery, but HOW and WHERE is it stored)?, 8 on page 800 and problems P26.30, 32, 35 on pages 802 and 803
ANSWERS:


STUDY GUIDE: 