2. CAPACITORS (look on PSE page 212) A capacitor is a device that can store electric charge and consists of two conducting objects placed near one another but not touching. A typical capacitor consists of a pair of parallel plates of area A separated by a distance d. Often the two plates are rolled into the form of a cylinder with paper or other insulator.

3. The capacitance of a parallel-plate capacitor can be found by using this equation: ε o = 8.85x10 -12 C 2 /Nm 2 To increase capacitance… -increase area of plates -decrease gap between

4. If a voltage is applied to a capacitor it becomes charged. The amount of charge acquired by each plate is proportional to the voltage. C is the capacitance in farads (F), Q is the charge in (C) V is the voltage (V) I like to remember as Q=VC Michael Faraday (1791-1867)

5. Applications of Capacitors: Keyboards and Defibrillators Charging… clear…

6. SAMPLE A capacitor whose plates are 12 cm x 12 cm separated 1 mm by an air gap. Find the charge on each plate if the capacitor is connected to a 12 V battery. = (0.12 x.12)/0.001 = 1.27x10 -10 F Q = CV = 1.27x10 -10 (12) = 1.53x10 -9 C

7. Example: A 127 μF capacitor is connected to a 12 V battery, find the charge on each plate. Q = CV = 127 x 10 -6 (12) = 1.52 x 10 -3 C practice problems

8. BASIC VOCAB: is the measure of electron flow. It is measured in amperes or amps. 1 amp = 1 COULOMB/second. I = Δq Δ tI = V/R is the amount of potential energy that each unit of electrical charge has AKA potential difference. It is measured in volts or V. V = W/qV = EdV = IR (AKA LOAD) is a force or device that slows down or uses electron energy. It is measured in ohms or  = Volt/amp or V/A. R = V/I The resistance produced by an object depends on: –M–Material –L–Length (longer = more) –W–Width (larger = less) –T–Temperature (higher = more)

9. I = V/R or V = IR R = resistance –U–U–U–Units: Ohms V = voltage –u–u–u–units :Volts I = c cc current –u–u–u–units : A AA Amps (Amperes)

10. the amount of work done in a given amount of time. is VOLTAGE times CURRENT Power has the units of WATTS, W or J/s. ** Remember voltage has the units of Volts or V and current is Amperes, Amps or A. Formula for electrical power is on formula chart. P = VI P = W/ΔtP = ΔqV/ Δ t

11. EX: A 12 V battery produces a current of 0.2 amperes. What is the power in the circuit?

12. AKA electrical work. is POWER times TIME. Its units are KWH, so have to convert your power if it is in WATTS. Its formula is on the formula chart. E = P x t

13. EX: A toaster operates on 2 amperes of current on a 110V circuit for 3 hours. Calculate the electrical energy used by the toaster. – 1. Calculate power. – 2. Convert – 3. Calculate Electrical Energy

14. You use electrical energy (electrical work) and multiply it by how much $/KWH the utility company charges. There is not necessarily a formula but it is something you should be able to calculate.

15. EX: Let’s use the previous example for electrical energy that we calculated. If we are charged $0.05/KHW, how much would it cost to run the toaster?