Electric Flux 3/26/2014

TODAY IS ALL ABOUT NUKING STUFF IN THE MICROWAVE YEEEA~!!!

After failing the fiesta due to falling asleep in class last time, We basically started

PROF GETTING READY TO RUMBLE!!

The candle does not get put away, all the energy goes into the flame.

Since CDs/DVDs have numerous little trenches, electric charges buildup therefore shattering the disk.

Once we acknowledge the different reaction that microwaves produce on different bodies, we realized that the Gauss’ Law in we learned not only exists in flatlands but is in Three Dimensions in the real world.  This explains why when metal conductor has excess charges, it can’t be inside.  We then started deriving equations for Electric Field Inside different 3D objects using Gauss’ Law.

Question 1: Electric Field Outside a Charged Sphere:

Electric field caused by this charge at a distance of 15 mm from the center of the sphere is 40,000 N/C

Question 2: Electric Field Outside a Charged Spherical Shell:

Electric field caused by this charge at a distance of 15 mm from the center of the spherical shell is the same.

Question 3: Electric field inside the charged spherical shell:

Magnitude of the electric field at R = 5 mm from the center of the electric field inside the spherical shell is 0.

Question 4: Electric Field Inside a Charged Solid Sphere:

a) Determined the electric charge inside a 5.0 mm radius Gaussian surface as 1.25*10^-10C

b) Determined the electric field 5.0 mm from the center of the charged sphere as 45,000 N/C

Question 5: Electric Field Inside a Charged Solid Sphere:

Show that the electric field INSIDE the solid uniformly charged sphere varies as E = [k Q/(R_{charged sphere})²]

Electric field inside of various shapes/distribution such as cylindrical or uniform bar....

In a nutshell, the net charge inside a conductor is 0 because all the electric charges equals out at the outer surface.  In the case of an insulator, it is more complex and needs calculation.  The most common shapes are sphere and cylinders:

Derivation using Gauss’ Law technique.

We continued "nuking" stuff such as candle, metal hair, soap, etc and really stinked up the room.  It turns out that microwaves can affect water and fat bond very effectively that's why it's so good to heat up Rudy's pizzas lol.

Finally, last but not least:

SUNCHIPS RAMPAGE!!!! x'D

Gauss' Law 3/24/2014

Today, we started with how Electric Field has impact on electrons.  We warmed up with a small demonstration of how old CRTube monitors work as the motion of a charged particle in a uniform electric field is being attracted across the display.

a CRT thing tube

Prof Mason tweaking the monitoring machine

We then were introduced to Electric Dipole in an Electric Field.  This dipole moment is defined as the product of the magnitude of charge and the distance of separation between the charges.  These are all a preparation for the main attraction-  ELECTRIC FLUX.

Our class experiment involves hanging some foils both the outside and inside of a metal cylinder.  We tested the reaction when the van de Graff generator is turned on, putting large negative charge onto the cylinder conducting onto the foils.  The result??

Only the outer foils will move away from the cylinder because the electric charge moves to the outside of the cage, leaving no net charge on the inside. Therefore no effect is felt by the foils on the inside of the cage.

The nail bed apparatus to determine how many uniformly spaced flux lines will pass through an imaginary surface area as a function of the angle between the direction of the flux lines and the normal vector representing the surface area.

The nails represent the electric field and the flux is perpendicular to it.  (area of the flux surface made by the wire hanger). Using a ruler and tangent, we measured the angle made with the surface and graphed how the angle changed with respect to the amount of nails covered by the enclosed wired surface.  We used a wire square as it contained 49 nails, the angle of the normal vector in this case was obviously 0 degrees. We then angled the wire so that it contained 42 nails and determined the angle. We continued to do this in decreasing increments of 7 nails until we reached zero and then used symmetry to determine the angles of up to -49 nails.

We constructed a graph of electric flux vs. the angle of the normal vector. These points were plotted in LoggerPro and a graph was constructed.  The graph is similar to the cosine function. This graph makes sense because the electric flux through a surface can be expressed as EAcosTheta.


Finally, we wrapped up the day with some Active Physics.  We conclude that the

In the simulation, the yellow ring is the surface across which we determine the electric flux. The flux is caused by the electric field, the green lines, caused by one or two electric charges. 

Electric Field 3/19/2014

After our fiesta today, we begin the topic on Electric Fields.  This should explain how charged objects can exert electrical forces on each other at a distance without contract.  Like as if they can "feel" the presence of another and detect its motion with only empty space in between....

We started off with the some same old "ActivePhysics" Java simulations:

Question 1: Explore the electric field

We summarized that our observations about the direction of the electric field produced by Q1 and Q2 being two POSITIVE point charges point away from each other.  Also, at different points in space as the distance between the charges increases, the field's magnitude decreases.

Question 2: Field due to single positive charge

We observed the direction of the electric force exerted by Q1 on Q2 and used the force shown in the simulation to calculate the electric field caused by Q1 at that point as

Question 3: Representing an electric field

Using only one single point charge and its electrical field and the field line, we developed some rules for the way that the electric field is represented:

• The direction of the lines as POSITIVE charges in the electric field points outward and NEGATIVE charges points inward.
• The electric field becomes weaker further away as the separation of the lines increases.  The outward it extends the region, the weaker the magnitude of the field in that region
• The magnitude of the field on a line being straight, showing a linear proportional relationship and also the same relationship to the area of dark region next to the lines.
• We analyzed and saw that the larger the magnitude of the electric field the density of the field lines increases.

Question 4: Uniform Field

The word "uniform" was used in describing the electric field in the middle region between the plates due to the fact that the electric field appears the same throughout that region.

Question 5: Force on a charge in a uniform field

We observed the force appears to spread evenly in magnitude when q is moved directly below its present position so that it is near the bottom plate.  The uniform spacing indicates that charged field is the same near top or bottom.  By moving q down and comparing the force on it when in this new position, the electric field still remains constant, and q the same throughout.

Question 6: Force on a negative charge

After leaving q in the middle half way between the plates, moving q around to different places between the plates, we observe the direction and magnitude of the force and conclude the direction and magnitude of the force depends on the charges +/- therefore it is consistent with

HOCKEY TIME!!!  xD

Practice was a no brainer!!

Difficulty 1 was fairly straight forward.... Simply attract it towards the goal.  Got it with only two Negative Charges.

Difficulty 2 could be a bitch but with a bit of thinking "outside" the box, was able to ace it under one shot with one Negative Charge and one Positive Charge.... (through several loops thou)

Uuuhh~ screetshot says it all.... this is what happens when the Charges are FREE OF CHARGE $$$ lol!!

Electric Charge 3/17/2014

Today, we were finally introduced to electric charges.  We started with rubbing balloons on the professor's fury head to charge up the electric charges... As a result, the balloons were able to stick to glass.  We then did the same but this time, we approach the charged balloon to confettis (punched holes).  We see the confettis first were attracted but quickly bounced off the balloon.

    

The charged balloon introduces a charge separation on the glass surface due to realignment of molecules...

 Rubbing against silk or fur produces electric charges that attract or repell the little punched out holes.

Based on this "invisible" interaction between charged objects, we concluded that there is an electric force acting upon them.  Our first experiment was conducted using electrostatic forces between two pieces of scotch tapes.  We first taped two strips of scotch tape onto the table then quickly peeled the tape off to bring the non-sticky sides of the tape toward each other.  They ended up repelling.  We then did the same sticking two strips of tape on the table and overlap tapping another two strips of tape onto each of the strips.  The results are answered as follows:

 The distance between the tapes directly affect the interaction between them...

Saxon demonstrating the attractiveness and repulsiveness between two +/+ and +/- charged tapes

Using some and measuring values....

In our second experiment, we did the Electric Force Law Video Analysis Activity.  Before we began our actual analysis, we first derived the expression for the electric force acting on a hanging ball by using the free body diagram for the ball being suspended at an angle and simple trigonometry to come up with a way of calculating angle REMEMBER 4A??  Finally, the derivation can be seen here:

We then had to do the actual video analysis....

Plotting a graph of Electric Force vs. Separation Distance with Logger Pro

Logger pro was used to determine the repulsion force verses the distance in the movie of a charged ball being pushed toward another like charge ball.  Above graph show that the force of the electrical repulsion is inversely proportional to the square of the distance.

Finally, we show that Coulombs law demos the inverse relationship between the force and the distance we saw in the Logger Pro graph.