3/31 Week 6 day 1 GAUSS’ LAW

at the beginning of the class, the professor gives us a website to show the picture of different electic fields together. Then we choose three circles to find the Charge enclosed by the arbitrary surface and the lines of luex in and out of the surface in the second photo.

and we know that there is a relationship bewteen q and the flux, and we find the unit of the constant number k is c^2/N*m^2.

 in this photo, we find the relationship between q/e_0 and E*A

in this video, we show that at the right is a device called a Faraday cage. we can see three suspensions of aluminum foil chunks on pieces of string. Each of suspensions include a string passing over the top of the cylindrical screen with small rectangular chunks of aluminum foil, a few centimeters in size, attached  to the ends of the string. 
Before the cylinder is charged, in the first photo,we predict that only the outer foils will move away from the cylinder. When it is charged, we find we think is right. The reason is that all the charge is going outside. 
The second photo shows the details.

in this photo, it shows us that when when the metal is charged, the Q is on surface.

in this photo, we find the relationship between E and σ .

in this photo, shows us that when the radius becomes 2 times, what will change in the perimeter， area and volume.

in this photo, we find the Guess's law.

in this photo,  since 4πr^2 is the equation for the area of the surface of a sphere, what is the equation for dA,
we find the relationship between E and q and r.

in this photo, we use Gauss's law to find spherically symmetric charge distributions and the electric field.

in this video, the professor put the Steel ball into the microwav, we find that it fires.

in this video, the professor put a cd inside, after we take out the cd, it was totally broken.

in this video, the professor put a match with fire, but we didn't find any thing outside.

in this video, the professor put a bubble inside, we find the bubble bright and then fire.

Then we begin to do some questions about Geometry of cylinders. 
in this photo, a. we find the volume of a cylinder of radius r and length L is V=π*r^2*L.
b. we find the fraction of the charge with a radius of r/2 and total charge Q is q=r^2*Q/R^2
c. the surface area of the cylinder is 2πr(L+r)

in these two photos, we find the elecrtic field about the circle.

Conclusion:

In today’s class, we look at Gauss' Law and how it can be used in analyzing both electrical and gravitational fields and how they work. We also analyze relationship between the electric field given the charges of Gauss's law applying in different types of conducting materials. We calculating the magnitude of Earth's gravitational field, and realizing that it is the same value as gravitational acceleration. Many different materials are placed in a microwave and we can see the preferred paths of electrical discharges.