Capacitance Capacitors A capacitor is a device used

Capacitance

Capacitors A capacitor is a device used to store energy using charges and electric field. They are a number of uses for capacitors in our modern world: Pulsed Lasers/Weapons Help engines run Touch screens (like this SMARTboard) Filters for electrical circuits Capacitors work using the physics of capacitance.

Capacitance – the ratio of charges on a conductive plate to the voltage between the conductive plates. Capacitance is like Capacity The Capacity of a milk carton is the volume it holds Heat Capacity is the amount of energy an object can store without an increase in temp.

Capacitance Charge on Plate Potential Difference (Voltage) Radius 8. 854 x 10 -12 C 2/Nm 2 Area Separation v Unit: Farad Scalar

Capacitance

How a Capacitor Works Parallel Plate Capacitor Electrons move from the plate leaving it positively charged + + + - Electrons build up on the plate leaving it negatively charged Electric Field in Wire + Battery - We can change the capacitance by affecting the area of the plates, the distance between the plates, or the voltage of the battery.

Parallel Plate Capacitors + + + -

Dielectrics One way to increase the capacitance of a parallel plate capacitor is to insert an insulator (like glass) between the two conductive plates. This insulator is called a dielectric.

Dielectric cont. Capacitor with dielectric Dielectric Constant Capacitor without dielectric

Combinations of Capacitors Basic Circuit Symbols Wire Capacitor Battery Switch

Capacitors in Parallel Circuits are ‘stacked like pancakes. ’ C 1 C 2 C 3 Battery

Parallel Circuits

Capacitors in Parallel C 1 C 2 CEQUIV C 3 Battery

Capacitors in Series Circuits are placed next to each other. C 1 C 2 C 3 Battery

Series Circuits

Capacitors in Series C 1 C 2 C 3 CEQUIV Battery

Practice Problem