Understanding Electric Energy and Capacitance Demonstrations

1. Chapter 18 Electric Energy and Capacitance demonstrations

2. Electric Potential Energy • PE= -qEd • PEelectric= -qEd charge electric field strength displacement from a reference point in the direction of the field • Only for a uniform field • Another type of Mechanical Energy

3. + + Positive charge moves d through a uniform field Figure 18-2 from p667 E d

4. h Potential Energy: Electric vs Gravity  PEgravity = mg  h PEelectric = -qE  d m d earth

5. Unit analysis PE= -qEd • joules = coulombs newtons/coulomb meters • E is sometimes in so and so

6. Potential Difference • Potential difference is the change in electric potential measured in volts • V = • V=-E d Units: volts=J/C Units: volts= *m

7. Potential Difference in Charges and Fields sim -4.4 V 2.2 V/m

8. Capacitors • Device that stores charge • Capacitance is a measure of the ability to store energy in the form of separated charges

9. Capacitance Equations Q = total charge Units: farads = C/V 0 = permittivity constant (C2/Nm2) A = area of plate d = Distance between plates

10. Energy and CapacitorsEquations