Term
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Definition
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Term
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Definition
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Term
| Charges within Insulators and Conductors |
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Definition
Insulators - (such as dielectrics) charge motion is restricted within the
material.
Conductors - charges are free to move
throughout the material leading to currents |
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Term
| What does 'electrostatics' insinuate? |
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Definition
| It is assumed all charges we work on are stationary. |
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Term
What is assumed about insulating material?
What is assumed about conducting material? |
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Definition
Charge is assumed to be distributed throughout the volume of the material.
Charge is assumed to be distributed uniformly on the surface of the material. |
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Term
| Observation about the force field within a charged conductor. |
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Definition
[image]
There is no electric field or force
inside a charged hollow conductor. |
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Term
| Force between two charges |
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Definition
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Term
| What is an electric field E? |
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Definition
The lines of force surrounding charges in an electrostatic system. (volts per metre)
[image] |
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Term
| Equation for an electric field |
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Definition
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Term
| Electric field's behaviour towards infinity |
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Definition
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Term
| Superposition of electric fields all acting on a point |
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Definition
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Term
| What happens when an electric field is exerted across a dielectric? |
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Definition
[image]
Within the dielectric the charges balance, but the edges cause a weak electric field which opposes the original field.
The strength of E2 is:[image] |
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Term
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Definition
The permittivity [image] is defined as [image][image].
[image] is the relative permittivity, or the dielectric constant of the material. |
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Term
| What is the dielectric strength of a material? |
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Definition
In reality materials aren't perfect. If the electric field is very large, it will pull the electrons out of the molecules and cause the material to start conducting.
This is known as dielectric breakdown. The dielectric strength, Emax, of a material is defined as the maximum electric field it can tolerate before breakdown occurs.
Emax for air is 10^6 V m^-1. |
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Term
| What is electric flux density? |
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Definition
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Term
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Definition
Flux is the amount of a vector field going through an area.
[image]
If the field is always perpendicular to the surface, then the flux is the scalar product of the field and area. |
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Term
Gaussian surface 1 - a point (or sphere) of charge
What is Gauss's law? |
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Definition
[image]
Therefore Gauss's law is DA = Q.
Q is the total charge enclosed by the closed surface. |
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Term
| Why are the field lines on a line of charge always radially outward at every point on the line? |
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Definition
An infinitely long wire contains a series of static charges with density [image].
[image] |
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Term
| Gaussian surface 2 - Line of charge (static on a wire) |
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Definition
The line of charge is enclosed by the cylindrical surface of the wire, and as such the field is always perpendicular to the surface.
[image] |
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Term
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Definition
Within a charged thin walled shell/box made of a conducting material, charge always resides on the edges. And therefore, the cage encloses no charge.
Hence, a gaussian surface S inside the conductor must have zero lux through it. Thus, the electric field must be zero everywhere inside the shell.
[image] |
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Term
| Why are the field lines on a conductive plane always radially outward at every point on the plane's surfaces? |
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Definition
An infinitely large conducting plane contains a uniform static charge which is evenly distributed with a density of [image].
[image] |
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Term
| Gaussian surface 3 - Thin uniform metal plane |
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Definition
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