Gauss laws

Lab Day 11: 3/31/15: Gauss Laws

Purpose:We will look at electric field lines and the use of Gauss's law to interpret charge from a certain electric field. 

Electric Field Applet

In this applet, we look at the electric field lines caused by two charges. It is seen that there is a dipole in which the positive and negative charges cause lines to radiate away from the charge from positive to negative. The electric fields lines are shown in the white lines that go from the red and blue lines that radiate outward.

Activity: Gauss's Law on Flatland

We drew electric field lines of three point charges where the positive charge causes lines to radiate away from the charge while a negative charge will cause electric field lines to point inward. We then add three Gaussian surfaces and found the sum of the charges in each surface. The flux can then be calculated in each of the surfaces in order to find the net flux. 

Van Degraff Generator

The Van Degraff generator is used connected to a cage that has three suspensions of aluminum foil pieces attached to it. The picture on the right is called the Faraday's cage which was used to distribute charge to the metal conductor. We predicted that the aluminum foils will not move against the cage. 

The results were inconsistent with our predictions as the aluminum foils outside of the cylinder moved away from the cylinder while the foil inside remained still. The metal inside does not move because there is no electric field inside the conducting cylinder where the charge enclosed inside the cylinder is zero. According to Gauss's law, there would be an electric field outside the cylinder causing the aluminum foils to move away.

Should we Stay in the Car?

We look at another scenario where we look at a conducting metal. The charges will try to distance themselves farthest away in which the charges lie right on the ends of the conducting sphere. The charges can move freely inside a conductor, and when we are in a car that is similar to the Faraday cage, the charges will also be at the ends away from the person inside. Therefore, the person should stay inside the car as the charges lie on the other layer of the car(conducting metal). The lighting will therefore most likely flow toward the ground. 

Electric Field inside Insulator

We used the charge density to solve for the electric field by identifying how much charge is within a given radius r of the sphere. Therefore the charge distributed can be used to find the electric field of an insulator using its radius. 

We went further by using Gauss's law in terms of the earth and gravity. By taking the integral of the mass of earth over constant k and setting it equal to the integral of Y dA, we get the acceleration of gravity. 

In this part, the flux is equal to the integral of the Electric field vector dA which gives us the charge enclosed over the constant which shows the basic calculations applied to Gauss's law and point charges. 

Disc/Candle inside a Microwave

The disc is observed to have some damage and sparked when put in the microwave, the damage was done in the areas where the electric field was the highest. The candle got brighter when put in a microwave. Similarly in the fork the sparks were on the tips in which the electric fields was the highest. 

Conclusion: We looked at electric field lines and how they work. The idea of Gauss's law was applied in different types of conducting materials to see a relationship between the electric field given the charges. We can see that electric charges serves as electric sinks and sources for a given electric field. The charge inside a conductor is zero observed in the Van degraff experiment and the lightning scenario. To finish off, we also found that sparks in different materials are found when there is a build up of electric fields.