Ampere's Law, Coil, and Solenoid (22nd Day).

Spring 2015
Professor Mason
May 19 Class


Computer  Work (13.9 and 13.10)
In class, we were given several works to do on the computer. First, we had to type "active physics" on Google, then click on "University Physics," which has a link: (http://wps.aw.com/aw_young_physics_11/). We first need to pick part IV Electromagnetism; to do that, we need to click the bar at the top left corner and switch it to electromagnetism. First, we had to do 13.9, which is the electromagnetic induction. This picture attached below shows us the questions provided on section 13.9 as well as the magnetic flux simulation to play with in order to help us finish all the questions.

The answers for each question on section 13.9 are shown in the picture attached below.

In the beginning of class, we also were given some equations of [E = d(flux . B)/dt], [Flux B = Integral of B vector dA or Integral of B vector cos(theta) dA], and the last one was [E = -N(d Flux/dt or E = -N(d BA cos(theta)/dt)]. While we were doing this computer work, professor Mason showed us an experiment with big magnet and rod. The diagram of where the magnetic field and the force of the rod is going is shown in the picture above; the experiment is shown in the picture attached below. 

With the power supply attached to the experiment tool, we could set up the rod as much as we wanted to; for example, we could either make the rod move towards the big magnet or make the rod move away from the big magnet depending on how the professor set the power supply. 

After we finished computer work section 13.9, we continued on doing section 13.10, which is shown in the picture attached below. 

 The picture above shows a Motional EMF simulation for section 13.10, which is the Motional EMF; as well as the simulation in section 13.9, we could play with this simulation as well, such as adjusting the length, resistance, magnetic field, and velocity; we could also choose which graph would it provide for us (I E and flux).

 The answers for section 13.10 are shown in the picture attached above, except for question 13; question 13's answer is shown in the picture attached below. Based on the picture above, we found out an equation of [Induction I = -BLV/R].

Inductions Properties

 In this class section, we learned some things about inductions and inductor; one thing we found out about inductors is that inductors function like capacitors, but it stores energy by the magnetic field. We also learned that as V increases, I decreases; as B increases, back emf also increases; as number of coils increases, R also increases; finally, the bigger the coil, the bigger the resistance is.

 We also found out some new equations, and one of them is [C = Q/V = I(dB/dt)/V]; that equation comes from the three equations of Voltage, which are [V = L(dI/dt)], [V=IR], and [V = I(dB/dt)/C]. We were also given an equation for B solenoid, which is [B solenoid = Vo I (N/L)].

In the middle of the class, we were asked to do some calculations for induction of coil; therefore, we needed to use an induction of coil formula, which is [L = Uo N^2 A/ Lo (dI/dt)], which Uo is a constant of 1.25x10^-6, and L has a unit called "Henry." We also learned that there are ways to decrease and increase inductions in coil. Ways to decrease inductions are: 1. Reduce the distance of plates, and 2. put something in between the plates; ways to increase inductions are: 1. increase the area of plates, 2. increase the length, 3. increase the loop, and 4. increase the Uo permibility (insulator). Based on the picture attached above, we learned that inductor acts like nothing in a wire or coil (dI/dt = 0). 

Another Computer Work (14.1)

After we finished doing some calculations on inductions, we continued on doing the computer work section 14.1, which is the RL circuit. Similar to section 13.9 and 13.10, this section 14.1 also has a simulation called RL circuit simulation to play with. This time, we can adjust the R, L, and V in order to help us finish all the question through this section. The simulation is shown in the picture attached below. 

 The answers for section 14.1 are shown in the picture attached above.

For question #2, we took a picture of the answers on computer because we need the detailed answer, and it is shown in the picture attached above. For this questions, we learned that Faraday's Law states that if the magnetic flux through a region of space changes, an electromotive force, or EMF, is induced in the region. The direction of the induced EMF is such that if charge is present in the region, the EMF will drive the charge to create magnetic flux in opposition to the original change in magnetic flux. The magnitude of the induced EMF is proportional to the rrate of change of magnetic flux. 

For question #8, this is how we got 1.7 A through some calculations, and it is shown in the picture attached above. Based on this computer work section 14.1, we learned that if we double the inductance, the time increases, and if we double the resistance, the time decreases. Based on this work, we also learned that Time constant is perpendicular to 1/L; if Time constant equals to 0, it means that it is going slow; if Time constant equals to infinity, it means that it is going fast. In conclusion for this work, the formula we need to know is [Time constant = L/R].