Verification of Coulomb's law and Electric Fields

first I wanted to say that all the 4B students had their weekend ruined due to class being cancelled last Wednesday and could not wait for Monday so they could go back and learn more physics.

Electrostatic Discharges and Quantitative Verification of Coulomb's Law

Class started with a question as usual, the question asked was what would happen if we put a metal fan with pointed ends at 90 degrees on each propeller, on top of the Van de Graaffs generator. We did not have the propeller needed so the professor put an almost spherical metal piece in the microwave, contrary to what many people believed there was no explosion or sparks because of the shape of the metal, the he placed a piece of aluminum foil with a pointy end to the top and then turned on the microwave oven, that was when sparks started flying, luckily inside microwave. We observed that the electrons escaped from the aluminum to the top of the microwave. we concluded that in the spherical shape electrons could not escape but if there is a sharp edge the charge leaks through there.

Next we tried to recreate the Charles Coulomb's experiment to prove that the force interaction between two small spherical charged objects varies as the inverse square of the distance between the two spheres. Sadly the experiment did not work because it was a humid day and for the experiment to work we need low air humidity (boohoo!). But the brilliant professor mason had anticipated this could happen, and had a video ready. In the video we saw how the experiment was supposed to work. The as one of the spheres was moved closer to the one that was hanging from the pendulum the pendulum produced an angle. We made a free body diagram and found the horizontal electrostatic force in terms of mass, gravity, and the angle tetha. So we got

F=mg(sin(tetha)/cos(tetha)) = mg(tan(tetha))

then we found equivalent of tangent tetha in terms of the horizontal distance x and the length L of the pendulum and we got

F=mg(x/(square root(L(square)-x(square)))).

the we computed the charge q of the metal coated sphere using

k(q(squared)(1/r(squared))=mg(x/(square root(L(square)-x(square)))) we solved for q.

Electric Fields

We moved on Electric fields section 4.7.2. on the package professor Mason's confirmed that physics teachers had lied. It turns out there are no contact forces then proceeded to push me without touching me. Since physicists think that all atoms and molecules contain electrical charges all forces are thought to be electrical forces acting at very small distances. we defined an electric field as

E=F/q

where: E is the electric field and is a vector quantity

F is the electrostatic force and also is a vector quantity

q is a positive test charge( test charges are always positive)

then we drew vectors on both positive and negative electric field,

Superposition of Electric Field Vectors

Linearity is the fact that electric fields form charged objects distributed at different locations act along a line between the charged objects and the point of interest.

The principle of superposition is the fact that vector fields due to charged objects at different points in space can be added together.

Using these two principles we can calculate the value of electric fields due to point charges at different locations. we do this by first calculating the electric vector form each point charge and then summing all the forces of the individual electric filed vectors.

we combined Coulomb's law and the electric field formula and we got

E=(kq/r(squared))

We used excel to calculate the magnitude of an electric field were the charge and distances were given, we calculated the magnitudes from .5 cm to 10.0 cm in intervals of .5 cm. We then used the spread sheet magnitudes, the principle of linearity and the principle of superposition to find the resultant of the vector field E at each point for exercise 4.8.1.c.

We moved on to 4.9 and calculated the electric filed E with a continuous charge distribution on a rod with two charges in space. First we estimated using the spread sheet.Then we were given the equation E=kq/(d(L+d)) were told to set up an integral for E and solve it to to show that the equation relates magnitude of the electric field. we substituted (d(L+d)) with r(squared) and integrated with respect to r, the limits of integration were from d to d+L and we ended up with E=Kq/(d(d+L)) again. we used this equation to calculated the exact value of the magnitude of the electrical field E.

Surprisingly class ended and I could not believe it, this class is way too short. It made me sad I can not wait until Wednesday, time goes by way too slow when you are not physics 4B.

I can neither confirm or deny that joy smells.

BAM!!!!