11-13-2014 motors and magnetic fields

• The Hall Voltage is the potential created across a current-carrying metal-strip when the strip is placed in a magnetic field perpendicular to the current flow in the strip. (Actually, the magnetic field does not have to be totally perpendicular to the strip, the magnetic field only needs to have a component that is perpendicular.)
• When the majority of charge carriers are positive, they are deflected to the top of the strip so that the top of the strip attains a higher positive potential. If the majority of the charge carriers are negative then the top of the strip will become negative and the polarity of the Hall voltage will reverse. 

this is a saint louis style motor. it consists of a wire wrapped iron core on an axis spindle. the wire ends are connected to a split ring commutator. the split ring rotates between the fixed contacts as as shown.

11-4-2014 Magnetic fields and forces

This shows that no matter what, there is always two ends to a magnetic pole. They exist only in their relativity. if there is not a north pole then there is no south pole, but in a magnet they can never be removed or seperated.

This is metal fillings reacting to the magnetic field. showing that polarizing effects of the bar. mind blown.

just like electric fields, magnetic fields work in a similiar fashion.

electric fields have electric charge and electric flux.
magnetic fields have magnetic charge and magnetic flux
their relationship is circular.

this shows that the force created by a magnetic field and a current is a cross product. The force is therefor perpendicular and in the direction in accordance to the right hand rule, by pointing your hand in the direction of the magnetic field and then curling it in the direction of the drift velocity.

an example calculation, and an attempt to make an addition to the right hand rule, or possibly the left hand rule. no one knows anymore. this has become a dark place.

This shows that the magnetic field does not to any work on the already moving particles by creating the force. The cosine of phi is zero.

This is a microwave emitter, i dont remember why we got it out. oh wait i remember i think. it accelerates particles. by applying the magnetic field and the current, i think. anyways this thing is pretty awesome.

• Since the magnetic force always acts at right angles to the charges motion, the magnetic force can do no work on the charge. The B-field cannot speed up or slow down a moving charge; it can only change the direction in which the charge is moving.
• The general path of a moving charge in a constant magnetic field is that of a helix with its axis parallel to the direction of the magnetic field.
• If you stand in such a way that you are looking directly into the oncoming magnetic field, the a positively charged particle will be seen to rotate in clockwise circle where as a negatively charged particle will rotate in counterclockwise circle.

• The component of velocity of the charged particle that is parallel to the magnetic field is unaffected, i.e. the charge moves at a constant speed along the direction of the magnetic field.
• If the particle has a component of velocity parallel to the magnetic field, then its circlular motion will drift at a constant speed (equal to that of its parallel-velocity component, v_ll) along the magnetic field producing an overall helical motion. 

This video shows the effect of the currant and the magnetic field, and the cross product being the force in the upward position. 

If the current is changed or the magentic field is changed then the force is changed. Never cross the fields.

This is showing how a magnetic field going through a ring perpendicular would have no force on the system because it would cancel out, but if it is done at an angle, it could create a torque. which could be used to make a motor.

this chart shows the change in the force created by a magnetic field moving through a semi circle. At the zero and pi radians it is zero because the forces are either opposing each other or they are parallel. as well the sum of these is an approximation of the total force created by the current and the magnetic field.

10-30-2014 diodes and transistors

When the negative end of the circuit is hooked up to the N-type layer and the positive end is hooked up to P-type layer, electrons and holes start moving and the depletion zone disappears.

When the positive end of the circuit is hooked up to the N-type layer and the negative end is hooked up to the P-type layer, free electrons collect on one end of the diode and holes collect on the other. The depletion zone gets bigger.

A transistor is a semiconductor, meaning that sometimes it conducts electricity, and sometimes it doesn’t. Its internal resistance varies, depending on the power that you apply to its base. NPN and PNP transistors are bipolar semiconductors. They contain two slightly different variants of silicon, and conduct using both polarities of carriers—holes and electrons

The amplifier you just built was an analog amplifier.  The term “analog amplifier” refers to a circuit that can take an input voltage that can vary continuously over time and either boost the voltage or current to create a higher power output signal that also varies continuously over time.  Many ICs are digital rather than analog circuits.  Let’s explore the meaning of the term “digital.”

            Counting and displaying numerals, as in a digital watch, are operations that require a different type of electronic signal and circuitry than the continuously varying signal characteristic of audio electronics.  Digital electronics involves voltages that are either “on” or “off.”  The voltage is either zero (“off”) or at some other fixed voltage which is defined as “on.”  The 0 and 15 Volt digital circuitry you will be using will interpret any voltage greater than about 3 V as an “on” state and any voltage less than about 2 V as an “off” state.  One advantage of digital circuitry is that it is remarkably insensitive to stray variations or “noise.”  Thus, digital recorders, computers, and other modern digital devices are vastly more accurate and reliable than circuitry that attempts to reproduce varying signals.

When the base emitter junction is forward biased, a small current will flow into the base. Therefore holes are injected into the P type material. These holes attract electrons across the forward biased base/emitter junction to combine with the holes. However, because the emitter region is very heavily doped, many more electrons cross into the base region than are able to combine with holes. This means there is a large concentration of electrons in the base region and most of these electrons are swept straight through the very thin base, and into the base/collector depletion layer. Once here, they come under the influence of the strong electric field across the base/collector junction. This field is so strong due to the potential gradient in the collector material mentioned earlier, that the electrons are swept across the depletion layer and into the collector material, and so towards the collector terminal

This is a clean bread board. It has a bright future and infinite possibilities. Every hole is a new possible circuit that could lead to the next big thing. THE NEXT BIG THING.

electronics and oscilloscopesIntegrated Circuits, or ICs, are amazing devices in which tiny transistors (which you haven’t learned about yet), diodes, capacitors, and resistors are connected together with thin metal films to make elaborate circuits. The techniques for making ICs have improved so much in the past few years that we have advanced from having ICs to VLSIs (very large-scale integrated circuits). VLSIs have up to a million circuit elements in them and can do very complex things. When an IC is bundled together and put in a single package, it is often encased in black plastic that has two rows of connectors on it. Thus, an IC tends to look for all the world like a bug in the centipede or millipede family. You will be using several types of “bugs” in this unit.

Electronics is the sub-field of electricity that deals with the information contained in electrical signals, such as those that produce sound from a loudspeaker, a TV picture, or memory states in a computer.

            This unit is intended to provide you with a brief introduction to electronics, including some of the devices used in circuits and some of the ways you can transform electrical signals by designing and constructing circuits.  In the first part of this unit you will learn to use an oscilloscope, which is one of the most basic measuring instruments used in electronics to measure voltage changes.  Next you will explore analog electronics by constructing a simple amplifier to boost a weak electrical signal so that it becomes an audible sound when attached to a loudspeaker.  Then you will begin an exploration of some of the digital electronic components that provide the basis for the modern digital computer.  Finally you will use digital electronic components to build a stopwatch.  The projects in this unit might stimulate you to learn more about electronics on your own or to take a course in electronics.

This is an oscilloscope. It is an instrument who most usual application is to give a visual display of time varying voltages.

Integrated Circuits, or ICs, are amazing devices in which tiny transistors (which you haven’t learned about yet), diodes, capacitors, and resistors are connected together with thin metal films to make elaborate circuits.  The techniques for making ICs have improved so much in the past few years that we have advanced from having ICs to VLSIs (very large-scale integrated circuits).  VLSIs have up to a million circuit elements in them and can do very complex things.  When an IC is bundled together and put in a single package, it is often encased in black plastic that has two rows of connectors on it.  Thus, an IC tends to look for all the world like a bug in the centipede or millipede family.  You will be using several types of “bugs” in this unit.

This is a function generator using a speaker to generate sound with regards to an alternating currant.

By changing the frequency you can make the beat drop. Any physics 4B student, upon completing the class, is applicable to be a professional DJ and or hiphop musician artist, or what ever they are called.

These are subjectective observations from attaching the function generator to the speaker.

This oscilloscope is displaying a wave function such as sine or cosine.

this oscilloscope is displaying a square function. It is for squares.

When the x and y values are crossed, it can become a ring when the frequency and the period match up.

You will be given a mystery box with several terminals.  You need to make a diagram on your whiteboard showing what each of these terminals produces by making measurements with the oscilloscope.   Take a picture of this diagram for your Blog.

10-23-2014 Capacitors and capacitive circuits

A Capacitor is a device that stores electric charge and electrical potential energy.

• Capacitance is a measure of the ability of a device to store charge per unit of voltage applied across the device

This is the application of kirchoff's law. These capacitors are in parallel and they in turn have a negative effect on each other, this is the opposite of the effect of resistors in parallel, in which they total to a greater resistance.

The capacitance of a given capacitor is defined mathematically as the ratio of the magnitude of the charge, q, on either one of the conductors to the voltage, V, applied across the two conductors

Michael Faraday. Total Badass. 

Don't sleep in class. Ever. This shows that some capacitors or some circuits can be simplified just by redrawing them to recognize what is in series and what is in parallel.

• Given some circuit containing only capacitors, the objective is to find the capacitance of a single capacitor that has the same capacitance as combined capacitance of all the capacitors in the circuit. The combination of capacitors can then be replaced by its equivalent capacitance.
• The next step is to decide which capacitors are in series and which are in parallel - Series and Parallel Connections.

By using the rules of parallel and series capacitors you can reduce the various sub-combinations until you are left with a single capacitor

The exercise shows the charging and then discharging of a capacitor. How it charges very quickly and discharges very quickly, yet theoretically never gets fully charged or fully discharged.  

In this experiment, the capacitance is monitored so that a rate can be established for charging and discharging, and a relationship between Voltage and time can be seen.

10-15-14 DC circuit analysis

This is Carl Friedrich Gauss. Badass.

This is the application of gauss's law and other formula's. It was left on the board after someone else's class. Gotcha.

This the equations for circuits. resistance vs capacitance. series vs parallel.

• Determine which branches of the circuit have a different current flowing through them and attach labels to the currents flowing in each branch. Components in series will have the same current so there is no need to use more than one label in a series branch.
• Assume a direction for the current flow in each branch of a circuit. You do not have to know which way the current is actually flowing for your solution to be correct. If you choose the wrong direction and do the problem correctly, you will get a negative answer of the current. Meaning that the current is flowing opposite to your initial assumption.
• Apply Kirchhoff' s Current Rule to the circuit junctions. This means write down the equation(s) that relate the currents flowing into that junction with the currents out of that junction.
• Choose a closed loop in the circuit and pick a direction around the loop. Your choice is arbitrary in that you should get a correct solution no matter which direction you pick for the loop - either clockwise or counterclockwise. It will make the solution less confusing if you can chose the loop in the same direction as the current is flowing. However, it is often not possible to do this for every section of the loop
• Apply Kirchhoff's Voltage Rule to the loop. This means pick a starting point in a loop and go around it and write down the voltage gains and drops until you return to your starting point. It some instances a battery can be a voltage drop rather than a gain if its polarity is opposite loop direction you have chosen.
• If you have several variables to determine, you may need to choose additional loops and repeat the above. In the end you need to generate a set simultaneous linear equations to solve, one for each unknown variable that you will have to solve.

Remembering the Code:  There are a number of ditties that have been devised to help people remember the resistor code.  Some of them are too “colorful” for official publication and others are too boring.  A good compromise is found in the ditty “Bad Booze Rots Our Young Guts But Vodka Goes Well” in which the BBROYGBVGW sequence of first letters matches that for Black, Brown, Red, etc.

Kirchhoff’s Laws 1.   Junction (or node) Rule (based on charge conservation):  The sum of all the currents entering any node or branch point of a circuit (that is, where two or more wires merge)must equal the sum of all currents leaving the node. 2.   Loop Rule (based on energy conservation):  Around any closed loop in a circuit, the sum of all emfs, voltage gains provided by batteries or other power sources, (e = emf) and all the potential drops across resistors and other circuit elements must equal zero.

Kirchhoff’s Laws

1.   Junction (or node) Rule (based on charge conservation):  The sum of all the currents entering any node or branch point of a circuit (that is, where two or more wires merge)must equal the sum of all currents leaving the node.

2.   Loop Rule (based on energy conservation):  Around any closed loop in a circuit, the sum of all emfs, voltage gains provided by batteries or other power sources, (e = emf) and all the potential drops across resistors and other circuit elements must equal zero.

The center bulb will remain OFF. Because the two sides of the circuit connected by the middle wire are at the same potential, no current can flow in that wire, and the bulb will not be lit.

The fundamental feature for this circuit is that the potentials at the points on opposite sides of the switch are the same before the switch is closed. This can be seen by noting that the two batteries are identical and the two light bulbs are identical. Therefore, closing the switch does not do anything to the circuit.

Two important points are relevant to the explanation of this result. First, note that the potential at the point where the third battery joins the circuit of the other two remains the same when the switch is closed. This is so because all of the batteries are the identical, and the potential along the light bulb wire is divided equally between the bulbs because they are identical. Therefore, closing the switch does not do anything to the circuit.

10-13-14 potential of continuous charge distribution

This shows that V=k int(dq/r)=k int(dq/(x^2+a^2)^1/2)
replacing the r with an angular radius. as well the integration is for q and so the denominator can be pulled out of the integral and it become kq/(x^2+a^2)^1/2
BUT
dq=lambdadx
this way you can integrate along a rod instead of a disk
YAY!!!!1!

The potential from a continuous charge distribution can be calculated several ways.  Each method should yield approximately the same result.  First, we can use an integral method in which the potential dV from each element of charge dq is integrated mathematically to give a total potential at the location of interest.  Second, we can approximate the value of the potential V by summing up several finite elements of charge Dq by using a computer spreadsheet or hand calculations.  Finally, we can use Gauss’ law to find the electric field along with the defining equation for potential difference to set up the appropriate line integral.

            Again, let’s consider a relatively simple charge distribution.  In this case we will look at a ring with charge uniformly distributed on it.  We will calculate the potential on the axis passing through the center of the ring as shown in the diagram below.  (Later on you could find the potential difference from a disk or a sheet of charge by considering a collection of nested rings.)

There are several ways that you could evaluate this integral. If you have a program like Wolfram Alpha or Maple, you could get the symbolic solution directly. For example using wolfram Alpha you get the following
One way to see if our answer is in the correct ball park is to imagine that we replace the line charge with a point charge at the center of the rod. What is the equivalent magnitude of the point charge, given that it has to be equal to the entire charge of the rod

This is a huge mess.