AP Physics B : Understanding Electrostatics
Study concepts, example questions & explanations for AP Physics B
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Example Questions
Example Question #1 : Electricity
Charges A and B are placed a distance of 
A student places these two charges in a vacuum medium and measures 
The dielectric constant of glass is 
You can simplify this question tremendously by using the definition of a dielectric constant. Dielectric constant is defined as the ratio of the electrostatic force in vacuum to the electrostatic force in the medium (in this case glass).
The question is asking for the reciprocal of this value: the ratio of the force in glass to the force in the vacuum. Our answer is calculated by taking the reciprocal of the dielectric constant of glass.
Example Question #2 : Electricity
How much work is done by the electric field moving an electron along an equipotential surface with a potential of 
We must know the strength of the electric field to solve
Moving a charge along an equipotential surface will involve no work done by the electric field. The potential is constant throughout an equipotential surface; therefore, the potential difference experienced by the electron will be zero. Remember that energy is dependent on the potential difference.
If the potential difference is zero then the energy (and work) will be zero.
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