1. APHY202 9/21/2015 1 17.7 Capacitance   Ratio of the charge on a conductor to the potential difference between the conductors.   Units of farads (F) Usually in μF or pF (10 -12 F)

2. APHY202 9/21/2015 2 17.7 Capacitance   For a parallel-plate capacitor:   Applications: cameras, computers, TVs, noise filters, starter motors, etc.

3. APHY202 9/21/2015 3 17.8 Dielectrics   An insulating material placed between plates of a capacitor that increases the capacitance: C = κ C o   The polarization of the dielectric will cause an decrease in the electric field. Application: measure humidity in air

4. APHY202 9/21/2015 4 17.9 Storage of Electric Energy   Work done to move Δq through V is ΔW= VΔq Total work = ½QV   PE stored = ½QV = ½CV 2 = Q 2 /2C   The energy is stored in the electric field between the plates with a density of ½ ε o E 2. Defibrillators

5. APHY202 9/21/2015 5 17.9 Storage of Electric Energy 1 2 3 4 5 6 7 8 9 10 11 1) Battery Compartment 2) Capacitor 3) Transformer 4) Capacitor 5) Diode 6) Transformer 7) Neon Indicator Light 8) Capacitor 9) Resistor 10) Flash Tube 11) Transistors

6. APHY202 9/21/2015 6 17.11 The Electrocardiogram   Cell area ~ 10 5 m 2   Charge per surface ~ 10 -8 C   Depolarization

7. APHY202 9/21/2015 7 17.11 The Electrocardiogram

8. 9/21/2015 8APHY202