Welcome to the PER wiki page. For the group website, visit http://groups.physics.umn.edu/physed/
In this wiki, you will find peer updated instructions and discussions based on the major projects currently being researched at the University of Minnesota. The current major project is the “yet to be named” computer physics coaches version 2. To find the version 1 coaches, go to http://groups.physics.umn.edu/physed/prototypes.html for a preview.
This space is reserved for Coach creation hints and tips (when we get there, we will soon).
Please enter any questions on how to use the coach interface to develop or use coaches here. If you can answer the questions, please answer what you can. Evan Frodermann will take these questions and answers and place them in the user guide that follows these questions.
The following are suggested tips and guides in constructing coaches as developed by the group. It is broken into categories based on the problem solving guide the coaches are based upon.
Suggestions on the focus section.
Suggestions on the describe section.
Here is the instructor's guide for the coaches. Evan will take User questions and suggestions from the Q and A section of the wiki and place them into the guide to keep it organized.
To PER group members, sign up for 2 problem and find a context-rich problem which will work for that topic. Any approach works and likely will be written with multiple approaches in mind.
|Discrete Charges||1||Qing X.|
|Discrete Charges||1||Brett Buchea|
|Continuous Charges||1||Evan F.|
|Electric Force from Field|
|Discrete Charges||1||Qing X.|
|On a charge||1||Evan F.|
|On a current||1||Brett Buchea|
|Biot-Savart Law(?)||1||Jie Yang|
|Ampere's Law||1||Jie Yang|
When editing the problems, please rate the “difficulty” and apply the rating the difficulty To quantify the difficulty rating, apply the rules at http://groups.physics.umn.edu/physed/Research/CRP/crjudge.html
Also, try to put any textual problems in the appropriate category.
The following is an edited version of the chosen problem for the first coach to learn and test the program's capabilities. Feel free to edit it further. I made it a bit tougher because it is now a range of distances, not one fixed distance. Feel free to make it easier if we want.
You have been asked to determine where to place a sample in a prototype apparatus to implant He in semiconductors. To minimize the damage to the semiconductor, the doubly ionized He ions which are produced at 100000 m/s, must be going slower than 100 m/s when they hit the semiconductor sample. The part of the apparatus used to slow the He ions consists of a wire charged to 80 nC with a length of 10 cm. The very small semiconductor sample is placed along the axis of the wire at an optimal distance from its end. You look up the mass of He and find it is 6.7 x 10-27 kg.
Electric force: Discrete charges
You and a friend are doing the laundry when you unload the dryer and the discussion comes around to static electricity. Your friend wants to get some idea of the amount of charge that causes static cling. You immediately take two empty soda cans, which each have a mass of 120 grams, from the recycling bin. You tie the cans to the two ends of a string (one to each end) and hang the center of the string over a nail sticking out of the wall. Each can now hangs straight down 30 cm from the nail. You take your flannel shirt from the dryer and touch it to the cans, which are touching each other. The cans move apart until they hang stationary at an angle of 10 degrees from the vertical. Assuming that there are equal amounts of charge on each can, you now calculate the amount of charge transferred from your shirt.
Electric force: either (Leon)
As a science project, you've invented an “electron pump” that moves electrons from one object to another. To demonstrate your invention, you bolt a small metal plate to the ceiling (2.0 m above your head), connect the pump between the metal plate and yourself, and start pumping electrons from the metal plate to you. If the pump can transfer 1013 electrons each second, about how long will it take before you (with a mass of 60 kg) begin to rise into the air? For simplicity, you may assume that both you and the plate can be modeled as point charges.
Difficulty factors: 8 (Easy)
Electric force: Continuous charges (Leon)
You have been asked to review a new apparatus for use at a semiconductor ion implantation facility. One part of the apparatus is used to slow down doubly-ionized He ions (He2+), which are positive and have a charge twice that of an electron. This part consists of a thin wire bent into a circle with a radius of 3.0 cm that carries a uniform negative charge of –8.0 µC. The He2+ ions have a velocity of 200 m/s when they pass through the center of the wire circle while traveling perpendicular to the plane of the circle. A semiconductor sample with which the He2+ ions are to collide will be placed 2.5 mm from the center of the charged circle. To check if this device will be able to work, you decide to calculate the speed with which the He2+ ions will strike the semiconductor sample. To aid your calculation, you decide to assume that the wire circle is very much larger than the distance the ion travels and that any effects of the sample’s presence can be neglected. Looking online, you find that the mass of a helium ion is 6.7 x 10-27 kg.
Difficulty factors: 1, 8, 9, 11 (difficult)
Electric potential: discrete charges
While sitting in a restaurant you notice that some “neon” signs are different in color than others. Your artist friend tells you that the color of the light depends on which gas is sealed in the tube. You know that the color of light depends on it’s energy and different neon colors must depend on the structure of the different atoms of the gases. Suppose that atomic structure is as given by the Bohr theory which states that electrons are in uniform circular motion around a heavy, motionless nucleus in the center of the atom. This theory also states that the electrons are only allowed to have certain orbits. When an atom changes from one allowed orbit to another allowed orbit, it radiates light as required by the conservation of energy. Since only certain orbits are allowed, so the theory goes, only light of certain energies (colors) can be emitted. This seems to agree with the observations of your artist friend. You decide to test the theory by calculating the energy of light emitted by a simple atom when an electron makes a transition from one allowed orbit to another. You decide to consider hydrogen since it’s the simplest atom with one electron and a nucleus consisting of one proton. You remember the proton has a mass 2000 times that of an electron. When you get home you look in your textbook and find the electron mass is 9 x 10-31 kg and its charge is 1.6 x 10-19 C. The radius of the smallest allowed electron orbit for hydrogen is 0.5 x 10-10 meters, which determines the normal size of the atom. The next allowed orbit has a radius 4 times as large as the smallest orbit.
Difficulty factors: (easy- medium)
Electric Field with continuous charges.
A large aquarium is trying to utilize a shark’s ability to detect electric fields directly as a training mechanism to help control and manage sharks in their tanks. Their idea is to test the sensitivity of this detection by producing a well known electric field at a fixed distance from a positively charged rod. To estimate the electric field produced by the charge, you will find the electic field of a charged rod with a uniform static charge density with a given length. For simplicity, the trainer will point the rod directly at the shark so you are concerned only about the electric field a fixed distance from the end of the rod. What is the electric field produced by the rod at a fixed distance from the end of the rod where the rod points directly at the shark.
(or ask, how far away must the rod be to produce an electric field that is ####)
(or ask for the amount of charge needed to produce the needed field.)
Difficulty factors: 1, 2, 8, 11 (difficult)
Electric Field with discrete charges.
A device is placed on board a rocket as it launches into space to measure the density of the atmosphere as a function of height above sea level. It consists of two oppositely charged points a distance of 1cm from each other which ramp up from a magnitude of 0C until a spark bridges the gap if the breakdown field, the magnitude of the electric field at which the electrons are striped from the air molecules which allow for the spark gap to occur, can be described as a function of density via the function Eb(ρ)=A*ρ/ρ0 where ρ0 is the density of air at sea level and A=2.2*10^6 (N/C). What is the ratio of the density of air and the density at sea level as a function of the charge.
Magnetic Force: On a current
You are asked to calculate the tension in the line of a high voltage DC power line. The high voltage towers are separated by 100m. The wire has a current of 1A running through it, a mass of 20kg, and hangs such that it makes an angle of 10° from the horizontal at either edge, from tower to tower (Diagram may be necessary). At first you think you only need to calculate the tension in the wire due to gravity when you remember there is also a Lorentz force acting on the wire due to Earth's magnetic field. Earth's magnetic field in the region is almost exactly parallel to the ground and travels South to North. The current in the wire travels East to West. What is the net tension in the wire, from both gravity and magnetism. Assume the wire is straight when calculating the Lorentz force.
Difficulty factors: 6,8,9 (Medium)
Magnetic Force: On a current
You and a team of biologist are traveling to the south pole to study marine animals that live under the arctic ice during the winter. Along the way our advisor would like to take some measurements of the magnetic fields in the area and use them to compare against arctic bird migration patterns. Sadly your advisor asks you to build a such a device, known as a gaussmeter. The meter consists of a stiff 50-cm wire that hangs vertically from a conducting pivot so that it is free end makes contact with a pool of mercury in a dish below. The mercury provides an electrical contact without constraining the movement of the wire. The wire has a mass of 5.0g and conducts a current of 0.20A downward. What is the sensitivity of this gauss meter? That is, what is the ratio of the output to the input (In radians per tesla)?
Difficulty factors: 4,8,9,10 (Difficult)
Magnetic force: either (Leon)
You are helping to design a piece of equipment that will help aim beta particles (electrons) from a radioactive source at cancerous tumors in patients. You wonder whether it would be more efficient to use a uniform electric or uniform magnetic field to deflect the emitted electrons and decide to calculate the magnitude of the fields needed in the two cases. The electrons will emerge from the source with a kinetic energy of 2.5 keV and your apparatus needs to deflect their velocities by angles of up to 5°. Space constraints dictate that the length of the region with the E or B field through which the particles travel can be no longer than 40 cm. You will also need to determine the best orientation for the fields relative to the direction in which the electrons will be traveling.
[Perhaps better to break it up into two separate problems?]
Difficulty factors: 1, 3, 9 (medium)
Magnetic force: either (Leon)
You are part of a NASA team exploring ways to protect astronauts on a space station from high energy charged particles. One idea is to surround the outside of the station with a uniform magnetic field so that incoming charged particles are turned away before striking the station. You have been asked to figure out how large the magnetic field must be as a function of the mass, charge, and kinetic energy of the incoming particles. Because of structural constraints, the magnetic field can extend no more than half a meter beyond the hull of the station. As a first approximation, you decide to make the calculation for the case in which the high energy charged particles have velocities that are perpendicular to the side of the space station.
Difficulty factors: 1, 2 (easy)
Magnetic force: Discrete charges
A scientific research group is trying to understand the properties of antimatter to find differences between matter and antimatter. The requires that anti-matter can be stored and accessed on demand. As an engineer, you are tasked to design and build a storage facility capable to this task. You want to store 1000 anti-protons and you cannot put them in your pocket, or they will annihilate with the protons the pocket is made of. Your plan is to use a magnetic field, and put them in a “parking circular orbit“ in a circular region of area, A. The magnetic field is supplied by a large electromagnetic which provided a constant magnetic field. The anti-protons are produced in different facility with an average kinetic energy of K. If the applied magnetic field is B, what is the minimum size of the facility needed to store these anti-protons? The anti-proton has exactly the same properties (mass (m), and charge (q)) of the proton. (EF)
Difficulty factors: 1, 2, 3 (medium)
Magnetic Field (Biot-Savert Law)
You are continually having troubles with the CRT screen of your computer and wonder if it is due to magnetic fields from the power lines running in your building. A blueprint of the building shows that the nearest power line is as shown below. Your CRT screen is located at point P. Calculate the magnetic field at P as a function of the current I and the distances a and b. Segments BC and AD are arcs of concentric circles. Segments AB and DC are straight-line segments. Difficulty factors:(medium)
Magnetic Force - Faraday's Law
You have a summer job working at a company developing systems to safely lower large loads down ramps. Your team is investigating a magnetic system by modeling it in the laboratory. The safety system is a conducting bar that slides on two parallel conducting rails that run down the ramp. The bar is perpendicular to the rails and is in contact with them. At the bottom of the ramp, the two rails are connected together. The bar slides down the rails through a vertical uniform magnetic field. The magnetic field is supposed to cause the bar to slide down the ramp at a constant velocity even when friction between the bar and the rails is negligible. Before setting up the laboratory model, your task is to calculate the constant velocity of the bar sliding down the ramp on rails in a vertical magnetic field as a function of the mass of the bar, the strength of the magnetic field, the angle of the ramp from the horizontal, the length of the bar which is the same as the distance between the tracks, and the resistance of the bar. Assume that all of the other conductors in the system have a much smaller resistance than the bar.
Difficulty factors: (medium)
You have received the electronic schematic for an implant device you are testing. Part of the electronics has a capacitor as shown below. You worry that the amount of energy stored in the capacitor might be dangerous to the surrounding tissues if something goes wrong. To satisfy yourself that there is no danger, you decide to calculate the maximum energy stored in the capacitor for R = 50 ohms, a 0.01 microfarad capacitor, and a 1.5 volt battery.
Difficulty factors:(medium) kh
This section is reserved for discussion on the electromagnetism coaches and common mistakes to be addressed in future coaches.
Based on discussion, these are the generalized common errors that may or may not be addressed with future coaches.
This section is reserved for discussion on the current mechanics and a to do list of corrections.
Based on discussion, these are the generalized common errors that may or may not be addressed with the current set of coaches.
The following are instructions on how to install a local copy of the v.2 of the computer coaches which utilizes Flash and Java for the program and MySQL as a database which stores the coaches information as well as student progress. The instructions are not platform specific and where platform specific instructions are needed, it will be indicated properly. Eventually links to screenshots will be included as links to help with the installation process.
This installation is necessary if you wish to create and edit Physics coaches with the newest version. However, this version of the installation does NOT include editing software which can change the coding of the coach creation editor. Instructions for these are later in this wiki.
Table of Contents
APACHE Server TOMCAT The local web server (Apache) with Java (TOMCAT) packages
MySQL A common database server
<property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver" /> <property name="hibernate.connection.url" value="jdbc:mysql://localhost:3306/(DATABASE_NAME)" /> <property name="hibernate.connection.username" value="root" /> <property name="hibernate.connection.password" value="1234" /> <property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect" /> <property name="hibernate.default_schema" value="physicstutor" />