1. Physics Section 17.2 Apply the properties of capacitors Consider two parallel plates connected to a battery as shown below.

2. Practical uses of capacitors include: The flash in a camera A TAZOR or cattle prod Tuning the frequency of a radio A microwave oven, x ray machine, MRI machine A source of energy to start an electric motor C = Q C = capacitance (farad F) V Q = charge (C) V = potential difference (V) A farad is a coulomb per volt. Capacitance is the ability of a conductor to store energy in the form of electrically separated charges

3. Most typical capacitors have capacitances in the range of microfarad to picofarads. μF = 1 x 10 -6 F pF = 1 x 10 -12 F The capacitance of a capacitor depends upon both the area of the plates, their separation, and the type of material between the plates. C = ε o A C = capacitance (F) d A = area of one plate (m 2 ) d = distance between the plates (m) ε o = permittivity of the medium between the plates (vacuum) 8.85 x 10 -12 C 2 /N m 2

4. The charge on a capacitor’s plates is directly proportional to the area of the plates and inversely proportional to the separation of the plates. By using an insulator (dielectric) between the plates a larger charge can be placed on the plates.

5. http://www.youtube.com/watch?v=ZYH9dGl4gUE http://www.youtube.com/watch?v=ZYH9dGl4gUE Note: A capacitor is discharged when a conductor connects the charged plates. The amount of energy stored depends upon the potential difference between the plates, the capacitance, and the charge on each plate. PE elec = ½ QV PE elec = electric potential energy (J) Q = charge (C) V = potential difference (V) PE elec = ½ CV 2 PE elec = Q 2 2C

6. A capacitor, connected to a 24 V battery, holds a charge of 72 µC on each plate. What is the capacitance of the capacitor? How much electric potential energy is stored in the capacitor?

7. A capacitor has a capacitance of 5.00 pF. a. What potential difference would be required to store 24.0 pC of charge? b. If the plate separation is 2.00 mm, what is the area of each plate?

8. Assignment Page 607 Problems 1,2,3