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Transcript of A capacitor is a device used to store energy using charges and electric field. They are a number of...
![Page 1: 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.](https://reader030.fdocuments.us/reader030/viewer/2022032600/56649da55503460f94a90993/html5/thumbnails/1.jpg)
Capacitance
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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.
Capacitors
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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
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Basic capacitance equation:
Capacitance of different objects: Isolated sphere
Parallel Plates
Capacitance
Capacitance 𝐶=𝑄∆𝑉
Charge on Plate
Potential Difference (Voltage)
8.854 x 10-12 C2/Nm2
Radius
Area
Separation
Unit: Farad Scalar Quantity
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Since charges are being held in place there is
also potential energy that is being stored (which can then be turned into kinetic energy of the moving electrons!)
Capacitance
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Parallel Plate Capacitor
We can change the capacitance by affecting the area of the plates, the distance between the plates, or the voltage of the battery.
How a Capacitor Works
Battery+ -
Electric Field in Wire
Electric Field in Wire
+++++
-----
Electrons move from the plate leaving it positively charged Electrons build up on the
plate leaving it negatively charged
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The separation between the two charged
plates creates potential energy.
The potential energy comes from the chemically stored potential energy in the battery.
Parallel Plate Capacitors
+++++
-----
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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.
Dielectrics
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This slightly changes our equation for a
parallel plate capacitor to look like this:
Dielectric cont.
Dielectric Constant
Capacitor with dielectric
Capacitor without dielectric
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Basic Circuit Symbols
Wire
Capacitor
Battery
Switch
Combinations of Capacitors
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Parallel Circuits are ‘stacked like pancakes.’
Capacitors in Parallel
C1
C2
C3
Battery
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Parallel Circuits have two important
characteristics:
The Current varies over each component in the circuit:
The Voltage stays constant over each component in the circuit:
Parallel Circuits
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To find the equivalent capacitance (a single
capacitor to replace all of the capacitors), we use the following equation:
Capacitors in Parallel
C1
C2
C3
Battery
Battery
CEQUIV
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Series Circuits are placed next to each other.
Capacitors in Series
C2 C3C1
Battery
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Series Circuits have two important
characteristics:
The Current stays constant over each component in the circuit:
The Voltage varies over each component in the circuit:
Series Circuits
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To find the equivalent capacitance (a single
capacitor to replace all of the capacitors), we use the following equation:
Capacitors in Series
C2 C3C1
Battery
CEQUIV
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What is the potential difference between the
plates of a 3.3 F capacitor that stores sufficient energy to operate a 75 W light bulb for 30 seconds?
Remember: Power =
Practice Problem