Electric Fields

It was a difficult day because on of our lab group members were missing. But on September 23rd, 2014, Physics 4B of Mt. SAC covered the topic of Electric Fields.

Electric Fields:

We were first asked to describe the gravitational field. Of course, everyone struggled because there really was not formal definition of a gravitational field.

Using some of the definitions provided by Professor Mason, we were able to describe what electric fields are.

Below is Professor Mason describing the shape of a positive and negative charged particles. Notice that one is bulging out of the plastic sheet and the other is bulging in the other direction. Interestingly enough, these were produced in a vacuum packing machine. If a marble, representing another positive particle, were to be placed on top of a positive bulge, the marble will roll off and land inside the negative bulge. This demonstration represents the behavior of charged particles.

Below is a simulation that demonstrates the behavior stated above.

Below are six questions we answered on the Activ Physics website.

 

Superposition Principle:

Below, we were introduced the idea of the Superposition Principle. This principle allows us to add all of the given particles to reach a net.

This is a problem to exemplify the use of the Superposition Principle.

We used an excel spreadsheet to find our various E's for this next exercise. We basically utilized the Superposition Principle to find the net E in this example. We were given four charged particles and two electric fields. Using resultant vectors, we were able to find the net E (shown in the next photo).

Conductors:

We were then asked what would happen if three negatively charged particles were placed on a metallic surface. It turns out that the three negatively charged particles will find a place on the surface that is the furthest away from each other causing an equilibrium within the surface. However, on a wooden surface, the negatively charged particles would stay in place.

Using the excel spreadsheet again, we were told to find the values of dQ, r, dx, and L. The end goal was to find the magnitude of the electric field, however, for our group, we failed to find what was necessary due to a lack of understanding of the concept and the program.

This was the original problem.

We were then asked to integrate the magnitude of the electric field equation in relation to dr.

We were then given a problem to solve using the found equation.

Electric Field Hockey:

This is a picture of a goal made in Electric Field Hockey Lv. 2. In this level, we used a total of three charges.

This is a picture of a successful level three on Electric Field Hockey. It was difficult; it took us a total of seven charges and close to two hundred times but we did it! What I found was that the effect of the positive and negative ions are great on another ion, which made the exercise difficult. For this level, we utilized the electric vector field to make our predictions of where the puck would go a bit more accurate.

Electrostatic Forces

On September 18th, 2014, Mt. SAC's Physics 4B class was introduced to the topic of electromagnetism.

Electrostatic Forces:

Professor Mason began the class by rubbing a balloon with some animal fur. He asked us if the balloon would stick to a glass cabinet door. We concluded that the balloon would stick and it did. We also included a free-body diagram of the situation.

Next, he rubbed the balloon with a silk handkerchief and were asked the if the balloon would stay this time. We concluded that it would not but the balloon did actually stick to the glass window.

We were then asked to attempt to explain mass and charge to a seven-year-old. Below is our result.

Next, we looked closer at electrostatic forces by using four pieces of scotch tape. First, we were asked to put together two pieces straight from the dispenser on their non-sticky side. They repelled each other.

We then though the lab manual told us to keep the bottom strip of tape on the table and attempt to put together the two top strips on their non-sticky side. The two strips were attracted to us and not each other.

We then did it correctly and compared the two bottom strips together. They repelled each other whereas when the top and bottom strips were put together, they attracted.

Electric Force Law Video Analysis:

By using our knowledge from the previous semester of physics, we were told to find an equation to find theta. Our group came up with this equation:

And then, using the found equation, to find the force of the pull required when pulling back a child on a swing.

These are the equations that my group found and thought would be useful.

By using Logger Pro, we analyzed the video of a charged ball approaching a ball on a string.

This is our force by time graph.

And this is our Separation of Distance versus time graph.

We put together the Force, Separation of Distance, and the change of Distance versus time.

And this was our Electrical Force vs. Separation Distance graph. When we did the curve fit, however, we did not find our constant to be anywhere close to the accepted value. Somewhere, our equation for one of the graphs were wrong and when we fixed it, we found it to be .001% off from the accepted value.

This is our conclusion of the lab.

Coulomb's Law:

We were then told to find the charges of two particles with given information.

We were then told to draw vectors of two particles with the same directional charge.

Next, we were given some information and were told to find the force done on one particle.

And then, we were asked to recall information from the previous physics class to find the force of two particles in vector notation based on a graph.

Van de Graaff Generator and Storm Ball:

Next, Professor Mason demonstrated to us a Van de Graaff generator. This generator generated certain amounts of electrical energy, enough to raise the hairs of this wig.

And spin the Franklin motor. It spun because the electricity expelled through the curved outlets of the apparatus causing a force to push the apparatus.

It also slightly raised the streamers of this makeshift pom pom.

This is the inside of a Van de Graaff generator (the ball removed).

We were then asked to explain how this generator worked.

Next, Professor Mason showed us a Storm Ball. Unlike the Van de Graaff generator, this generator kept the electricity inside an insulated space and thus, no one was shocked.

We were then to find a ratio between the force and the radius of charge and gravity. It was found that the force of charge was much stronger than the force of gravity.