Electric Flux

We have already learned the basics of electric field lines, vector fields. Below are representations of an electric field in equation form in two dimensions and three dimensions. Also, through an activity, we have found that the amount of flux lines are proportional to the amount of charges that are on the field. To be more precise, we have found there to be five flux lines for every charge.

Below is a representation of Gauss' Law. This picture shows that within a closed surface, there is no charge within the surface but there is some surface outside of the surface, which is Gauss' Law in practice.

We were then asked a profound question. Hypothetically, let's say you were driving down a highway in the middle of a thunderstorm. What would be your best choice of action to evade getting shocked? Choices one through four had the person in question get out of the car, resulting in the person receiving some charge since they now exited an enclosed surface (the car). Gauss' Law states that it is the safest to stay within the car so as to not get shocked.

We were then asked what would happen to a metal fork if we put it inside of a microwave. We predicted that nothing would happen because the electrons would deflect off the surface.

And we were correct. It only got slightly warm.

Next, we were asked what would happen to the CD.

We didn't think anything would happen because it was also metal but when it came out of the microwave, we were wrong. The CD had holes in it!

What then a lit match? We predicted the fire would become larger.

The fire did indeed get larger but only for a short while. Part of the reason why it got larger was because it created plasma balls. These occur when water vapor that is emitted becomes super heated from the fire. The heat from the microwave aided in the super heating of the water vapor which resulted in the plasma balls that we see in the microwave.

We were then asked to derive the equation for a volume of a circle and a sphere to find the relation of Gauss' Law to calculate the electric field. It turns out that it is larger than a circle's area by a factor of four.

Below is our derivation of an electric field to find an equation for a circle and sphere.

We were asked what would happen to a bar of soap when it went into the microwave.

What would happen to an empty juice pouch?

We were then asked if radius is 0.015 mm and the charge was 10*10^10, what was the electric field that was produced? We found the answer to be 40,000 N/C.

These next few exercises are all Activ Physics exercises. They include this app shown below.

What is flux when everything is zero? Well, it would be zero.

What is the charge on the inside of the surface? When rho, density, equaled Q / V, Q on the inside equaled 1.25*10^-10 C.

What is the magnitude of the electric field? Constant k times charge on the inside divided by radius squared: 45,000 N/C.

What is electric field in terms of k, Q, R, and r? E = kQr/R^3.

What is the relationship between the inside surface charge and the outside surface charge? Inside charge is equal to one fourth of the outside charge.

And what is the generic electric field equation for a rod? We found E to be sigma divided by initial epsilon times two pi.

Introduction to Magnetic Force

Our introduction to magnets began by determining what the comic joke meant to represent. My guess was right: a bar magnet. Carlos decided to put "Magneto from X-Men."

On a more serious note, we were asked to sketch the relationship of a compass and a bar magnet  with lines. In addition to the lines, we also found that the North pin was attracted to the South side of the magnet.

Using iron filings, we were able to visually see the magnetic field lines created by the magnet.

We were then asked to find the flux lines using Gauss' Law. In the surface encompassing the whole field, the flux was zero. The flux encompassing only one side of the magnet had the flux equal to the lines that were inside it.

The compass.

The compass and a magnetized pin that was broken in half. It turns out that even though according to Gauss' law there has to be only one magnetized side when the magnet is cut in half, a magnet will always have a North and a South side. It is physically impossible to create a one sided magnet.

These are the equations for an electrical and magnetic Gauss' Law. With our findings from earlier, it is concluded that the net magnetic flux will always be zero.

Professor Mason then used a bar magnet to manipulate the electron inside a cathode tube. The electron movement was always perpendicular to that of the bar magnet.

That physical evidence shows that the relationship between a magnetic field and a charge will be a cross product: F = qV x B ( F, V and B being vectors).

Using the right hand rule, we are also able to determine in which direction each vector points.

We were then given a sample problem. The goal was to find the force and remembering that phi is equal to 90 - theta, we were able to find the force on this particular equation to be 6.24 * 10^-16 in the negative direction.

This is a microwave gun. A power source emits electrons into the antenna which then produces a microwave.

This is the front view of the microwave gun. It was safer NOT to shoot it in the lab.

This is a very strong horse shoe magnet.

If a wire was set up to run through the magnet and a current was also sent through, the wire would move up or down depending on the direction of the current. This is physically showing the force acting upon the wire when a charge is being interacted with a magnetic field.

Picture representation of the interaction is shown below.

This is the set up:

We were then asked what the force would be when a rectangular surface had a current running through it with some sort of magnetic field going inside the board. Using the right hand rule, the force would go in all directions, possibly stretching and compressing the surface.

And what if the same surface and current but the magnetic force was going to the left? Then there would be no force on points A and C but a force going into the board on point B and out of the board at point D. This interaction results in the surface to turn due to torque. However, when the surface is at 90 degrees, the surface will change direction and spin in the opposite direction.

When a wire is not straight, it is called a kinky wire. Because these wires are not straight, we have to use a different equation to find the force: dF = Idl x B.

With the given values, we were able to use excel to determine the total force being done on the wire.