(9/30/14) Electric Fields

Today we go further into the life of electricity and discuss Electric Fields, flux, and start understanding the complexity that is Gauss's Law

Class Activity - Relating Torque and Potential Energy to Electric Dipole

Deriving pxE

By understanding the idea of torque, used all the way back from 4A as a way to calculate rotation, we can then rebuild the equation τ = r x F (a cross product), we can then use the idea of work, and obtain the new equation τ =pEsinθ, knowing that sinθ creates a cross product, obtaining
τ = p x E

Deriving p·E

Similarily we can do the same thing that we did for torque with potential energy, obtaining the equation pEcosθ, which we know it to be a dot product U = p·E







Class Activity - E-field in a metal canister

Set up of experimentation

In the next activity, we were to place a metal canister (shown on the right) next to a Van De Graaff (shown on the left). The canister contained 3 tin foils inside and 3 tin foils outside.
The activity here was to see how the tin foils will react to the electricity produced by the Van De Graaff generator

Our initial prediction

We predicted that all 6 tin foils will react to the Van De Graaff generator and move as a result.
This prediction came as a result of what we thought we knew about E-fields, and that since its electricity and metal, they should react accordingly

A video of the experiment

A correction of our theory

We learned that in fact only the 3 tin foils outside actually reacted to the Van De Graaff generator and moved as a result.
We learned that this came to be because of the fact that while inside the metal canister, the E-field actually turns out to be zero, while an E-field is generated outside the metal canister, causing the tin foil to move.



Class Activity - Electric Field Lines
We were asked to place a single charge in this simulator in order to understand electric field lines.

When we placed a positive +1 charge into the simulator and ran it, we realized that it gave us 5 field lines. We can also see that these field lines become denser as it gets closer to the particle, most likely due to the fact that the close the lines are to the charge, the stronger the magnitude of the charge becomes. We realized that as we increased the charge, the lines increase by an increment of five.

When we placed two particles of opposite charge, we get that these five lines react to each other, the closer the lines are, the more the lines bend to the opposite charge. We also can state the same reason as before as to why the lines become more dense as it becomes closer to the charged particle.




Overall, we can state that the field lines represent our vector, the direction in which the electric field travels, with it being stronger as it get closer to the charge

Class Activity - Flux as a Function of Surface Area
In order to speed up the process of learning flux, Professor Mason taught us the idea of the proportionality between flux and angle through a simple experimentation

Fun video showing distribution of weight to a nail bed

He used the nail bed to act as a charged electric field, and a square wire to act as the area enclosed. By having the angle at 0 degrees, it is shown to have the most amount of charge enclosed. Subsequently, when the angle reaches 90 degrees, it is shown to have zero charge enclosed.







Class Activity - Flux Simulator
In our last lab, we worked on answering questions about flux within a simulator provided for us.

Answers to questions 1-4

Answers to question 6 and 7

Additional Events
On Friday, September 26th 2014, SPS (Society of Physics Students) invited a guest speaker Prof Seiji Takemae to talk about his research on Raman Spectrometers and their future usefulness. As a result, he also allowed a selected few students (myself included) to take part in his future research pertaining to this subject (Physical Chemistry).

His setup on evaluation carbon tetrachloride and Tylenol