1. Capacitance and Dielectrics
Any two conductors separated by an insulator forms a Capacitor.
Definition:
1F =1 farad = 1 C/V = 1 coulomb /volt
Chapter 24

2. Capacitors and Capacitance (Chapter 24, Sec 1)
Coul/m2
Figure 24-2
Farads
1 F = 1 x 10-6 Farads
1 pF = 1 x Farads
1 nF = 1 x 10-9 Farads
Chapter 24

3. Useful Definitions and Relationships
Chapter 24

4. Practical Capacitors Practical Values 100µF 1µF 0.01µF 100pF 1pF
Chapter 24

5. Some examples of flat, cylindrical, and spherical capacitors
See just how large a 1 F capacitor would be. Refer to Example 24.1.
Refer to Example 24.2 to calculate properties of a parallel-plate capacitor.
Follow Example 24.3 and Figure 24.5 to consider a spherical capacitor.
Follow Example 24.3 and Figure 24.5 to consider a cylindrical capacitor.

6. Capacitors in Series All capacitors in series have the same charge Q
Chapter 24

7. Capacitors in Parallel
All Capacitors in Parallel have the same voltage V
Figure 24-7
Chapter 24

8. Capacitors in Series and Parallel - Example 24.6
Chapter 24

9. Energy Storage in Capacitors
Let q equal the changing charge increasing from 0 to Q as the changing voltage v is increasing
from 0 to Vab. We will determine the energy stored in the capacitor when the charge reaches Q
and the voltage reaches Vab. (q and v are the intermediate charge and charging voltage
joules
Chapter 24

10. Transferring charge and energy between capacitors
Example 24-7, Page 827 Text
Transferring charge and energy between capacitors
Calculate the initial charge
Calculate the initial stored energy
Connect the capacitors
Calculate the resulting voltage
Calculate the charge distribution
Calculate the energy change
Chapter 24

11. Capacitor Dielectrics Solve Three Problems
Provides mechanical spacing between two large plates
Increases the maximum possible potential between plates.
For a given plate area the dielectric increases the capacitance.
Chapter 24

12. Dielectrics change the potential difference
The potential between to parallel plates of a capacitor changes when the material between the plates changes. It does not matter if the plates are rolled into a tube as they are in Figure or if they are flat as shown in Figure

13. What Happens with a Dielectric
V  V0 (Q unchanged)
Therefore: C  C0
Figure 24-12
(Definition of Dielectric Constant) (24-12)
(24-13)
Chapter 24

14. Dielectric Constants

15. Field lines as dielectrics change
Moving from part (a) to part (b) of Figure shows the change induced by the dielectric.

16. Induced Charge and Polarization
Inserting the dielectric increases permittivity by K, decreases E by 1/K and decreases energy density by 1/K
The E field does work on the dielectric as it is inserted. Removing the dielectric the energy is returned to the field.
Chapter 24

17. Dielectrics (Chapter 24, Sec 4)
Induced Charge and Polarization
(24-15)
(24-18)
Therefore: E  E0
Chapter 24

18. Dielectric Breakdown V = Ed Vmax = Emax d
where Emax is the dielectric strength of the dielectric
in volts/meter.
For dry air: Emax = 3 x 106 V/m
For Mylar, K=3.1, Emax = 9.3 x 106 V/m d
Chapter 24

19. Dielectric breakdown
A very strong electrical field can exceed the strength of the dielectric to contain it. Table 24.2 at the bottom of the page lists some limits.

20. Electric Field Effect on Molecules

21. Polarization and electric field lines

22. Chapter 24

23. Chapter 24

24. Chapter 24