5/19 Electromagnetic Induction, Inductors

Purpose: The purpose of today's class is to look at inductance and electromagnetic inductors using activphysics and to look at how inductors work.

Electromagnetic Inductors

We started class by using activphysics to learn about the magnetic flux and induced emf. The change in magnetic flux caused an induced current or emf which is consistent with faraday's law. When the magnetic flux changes the most, we get the highest induced emf and when the angle between the magnetic field and the area is 90 degrees we get that there is no induced emf. Also the negative emf indicates a positive change in magnetic flux. 

Copper Rod Experiment

In this experiment, Professor Mason setup a rod that would move when connected to a supply of current. As a result when we gave the rod a current, the rod moved and when we changed the current direction, we found that the rod also moved in the opposite direction.

The whiteboard shows our predictions and the experiment was consistent as the rod reversed its direction when we changed the current direction by going inward. This is due to the fact that the force on the stick will be inverted as we invert the current direction. Using the right hand rule, we can see that as the magnetic field is pointing upward, we have a current going along the rod, we will get a force pushing out.

In the next activity, we look at motional EMF and answered the questions on the whiteboard and we see that the velocity is reversed as we reverse the current as seen in the previous experiment.

Inductors

Inductors are important because they serve as an energy storage in a magnetic field when there is a current in a wire. We define inductance as the negative emf produced by the inductor over the change in current.  We can then plug in the equation given the number of turens to calculate the magnetic flux. Therefore we can find the voltage gain and drop across an inductor using inductance 

We derived the emf using the lengh, area, and number of turns in regards to the changing current using these factors to identify the inductance.

Next, we looked at the inductance of a Solenoid and found with given values using the equation derived previously to solve for inductance knowing the number of coils, area, and length of solenoid.

We were able to identify the units of inductors using our equation and found that it is equal to one Henry.

After a long time has passed, we find that the current will eventually plateau and remain constant and goes toward infinity. The graph on the right of the board shows this relationship as voltage is the inductance times the changing current.

Finally we looked at activphysics again regarding RL circuits where we have resistors and inductors. We found that when an inductor is connected, we have an induced emf that is opposite of the emf from the battery supplying the current. As time increases, the inductance increases and as resistance increases the inductance decreases. The relationship is shown in the questions answered below. If the inductance is large, we get that the current will reach equilibrium slower than if we increase the resistance which will allow for the current to reach equilibrium faster. The relationship is confirmed in our time constant relationship with resistance.

Conclusion: By looking at activphysics, we learned that any current supplied will cause an induced back emf going the opposite direction as the emf supplied by the battery. Therefore, we can identify how forces in related to velocity and movement of objects in a magnetic field. We also found that by changing magnetic flux, we get an induced emf to oppose the changing flux. The second part of class, we learned about inductors and identified that inductors are useful in magnetic fields in order to store energy when there is a current supplied. We learned using the number of coils, area, and length the idea of self-inductance and solenoids. When inductors are added to the circuit seen in RL circuits, we find that it causes a change in magnetic flux which in turn produces a induced emf.