part 1 link http://www.walter-fendt.de/html5/phen/magneticfieldbar_en.htm

part 2 link http://www.thephysicsaviary.com/Physics/Programs/Labs/FieldFromWire/index.html

part 3 link https://phet.colorado.edu/en/simulation/faradays-law

part 4 link http://www.thephysicsaviary.com/Physics/Programs/Labs/SpinningCoilwGraphLab/index.html

part 5 link https://www.walter-fendt.de/html5/phen/lorentzforce_en.htm

links under part 5 for questions

1. https://www.youtube.com/watch?v=L5vdLmY-Yyc

2. https://www.youtube.com/watch?v=CQ5abgQtye0

3. https://www.youtube.com/watch?v=aL2hedsEQ6I

4. https://www.youtube.com/watch?v=ncUOIE9nqa4

5. https://www.youtube.com/watch?v=yl6XtJ6vELU

6. https://www.youtube.com/watch?v=N7tIi71-AjA

Experiments with Magnets Introduction In this lab, the student will investigate magnetic field direction and magnitude for a permanent magnet and a long straight wire. The student will be introduced to the concept of magnetic induction and will demonstrate Faraday's Law and Lenz's Law. The student will demonstrate the magnetic field accompanying an electric current in a wire, and look at forces on currents due to magnetic fields. Theory Magnetic Fields: The field of a magnet may be described in terms of magnetic poles. The magnet has a north pole and a south pole at either end. Opposite poles will attract each other while like poles will repel each other. If a magnet were to be cut into pieces, each piece would have both a north and south pole. The magnetic field may be represented by lines, just as with electric fields. The lines go between the north and south magnetic poles and their direction is, by convention, pointing from north to south. Unlike electric fields, magnetic field lines do not point in the direction of the force on a charge. Also unlike electric fields, there is no experimental evidence for the existence of a magnetic monopole. The SI unit for measuring the strength of a magnetic field, B is Tesla (T): IT = 104 Gauss. The needle of a compass is a small permanent magnet. If the compass is out of the immediate vicinity of local sources of magnetic fields, its needle will align itself with the Earth's magnetic field pointing to the south of magnetic pole of the Earth (and the geographic North). When electric charge is in motion, a magnetic field is established in the space surrounding it. For a long straight wire carrying a current I, the magnetic field at a distance r from the wire is given by: B = - Hol (1) 2 rr where uo is the magnetic permeability of free space. To determine the direction of the magnetic field lines surrounding a wire, point the thumb of your right hand in the direction that the current travels. Your fingers curl around the wire in the direction of the magnetic field. The field lines circle the wire. A solenoid consists of multiple (N) loops of wire with current I flowing through it. If the solenoid has length 1, the magnetic field within the solenoid is given by: B = HoIN (2) 1The direction of the magnetic flux from a solenoid can also be obtained by the right hand rule. Curl the fingers of your right hand such that they go around the loops of wire in the direction of the current. Your thumb will then point in the direction of the magnetic field. Procedure Induced Currents: Magnetic flux (@) through a surface is a measure of the magnetic field passing Part 1: Magnetic Field Direction through the surface. A magnetic field directed at an angle q to the normal to a surface with area A generates a magnetic flux of Go to http://www.walter-fendt.de/html5/phen/magneticfieldbar_en.htm (you may need to type this link directly into your browser, as sometimes cutting and pasting from PDF documents doesn't D = BA cos 0 (3 ) not work) Thus the flux is maximum when the magnetic field is perpendicular to the surface, and minimum A screen should load that looks as follows: when it is parallel to the surface. There are three ways to change the magnetic flux: to change the magnetic field, to change the area and to change the angle of the field to the surface. We will Magnetic Field of a Bar Magnet investigate all three of these in this laboratory. e magnetic field of a bar magnet can be investigated with a compass needle. The magnetic poles of both bar magnet and compass needle are symbolized by the lowing colours: Faraday's Law of Induction states that a changing magnetic flux will induce an emf & in a north pole red conductor with N turns of wire, proportional to the time rate of change of the flux, D. south pole green If you move the magnetic needle with pressed mouse button, the magnetic field line through the center of the compass needle will be drawn with blue colour. The blue arrows mark the direction of the magnetic field which is defined as the direction indicated by the north pole of the compass needle. If you turn the magnet by using the red 8 =-NAQ ( 4) button, the direction of the field lines will reverse. The other button makes it possible to clear all field lines. At If the conductor is part of a closed circuit, a current is induced in the conductor. This current Clear field lines creates its own magnetic field. The direction of the induced current is such as to oppose the cause producing it. This relationship is Lenz's Law. Turn magnet In Parts 4 and 5 of this laboratory, we will study the effects of changing magnetic flux on the voltage induced in a coil. There are several demonstrations of Lenz's law in the video clips in Part 6 of this laboratory. These will be described in that section. W. Fendt 2001 Magnetic Forces: As discussed above, an electric current generates a magnetic field. Since magnetic fields interact (like poles repel, opposites attract), an electrical current will feel a force on it in a magnetic field. The magnitude of the force, F, on a wire of lenth L, carry a current I in 1. Move the compass around the screen, and watch the way the needle points as you move a magnetic field B is given by: it. Is the red end of the compass a north pole or a south pole? 2. Every time you release the compass, the app will draw a magnetic field line with arrows F = ILB sin 0 ( 5 ) showing the direction of the field lines. In what direction do the field lines point? 3. Place the compass directly over one of the field lines on the screen. How does the needle Here, 0 is the angle between the current and the magnetic field. The direction of this force can be on the compass compare to the direction of the magnetic field lines shown screen? determined by the right hand rule: put the fingers of your right hand along the current direction, 4. Click "Turn Magnet" in the right hand bar. What happens to the direction of the and then bend them toward the direction of the applied magnetic field. The force will be in the magnetic field lines? direction of your thumb. Reversing the direction of current will reverse the direction of the 5. Move the compass around the magnet again. Do your results confirm the results from step 1? force. Two parallel wires with current flowing in them will also exert a force on each other: currents in the same direction attract, while opposite currents repel. 3Part 2: Magnetic Field Strength from a Long Straight Wire 4. Click the arrow to reverse the current direction, without moving the magnetic field sensor. Does the magnitude of the magnetic field change? What happens to the sign of the field? Go to http://www.thephysicsaviary.com/Physics/Programs/Labs/FieldFrom Wire/index.html, and 5. Next we will verify equation 1 for the magnitude of magnetic field as a function of distance click "Begin" A page will load that looks like the following: The solid gray bar represents a long from a current carrying wire. On the bottom bar, click the "Location of field sensor" and straight wire. The gray loops around the wire are the magnetic field lines. 'Current" boxes to open them. Your screen should look something like this: Magnetic Field from a Wire Lab Magnetic Field from a Wire Lab 3d Field 2d Grid Field Strength LabQuest @2 File Sensors Made Time Bases CH 1: Magnetic Field Rate 1.0 samples's Vernier rnier MAGNETIC FIELD ITIC FIELD 20.11 uT Distances cm) SCIENCE SYSTEM Field Strength Location of Field Sensor Direction (Electron Flow) Current Location of Field Sensor Direction (Electron Flow) Current Change to Conventional 5.5 A 1. Click in the red outlined box labeled "Direction (electron flow)", it will open and you will see a box as shown on the right. Click the red Direction (Electron Flow) You can move the field sensor location around the grid by clicking on the appropriate arrows. arrow, and notice that the direction of the small blue circles reverses You can also increase and decrease the current. Note that the magnetic field is located at the direction. What happens to the direction of the magnetic field lines center of the + crosshairs on the magnetic field sensor. when you reverse the electron flow direction? Change to Conventional a. Move the magnetic field sensor so that it is located at coordinates (1, 1). The first 2. In the same box, click on the words "change to conventional". Now, number in the brackets indicates the horizontal location (along the wire) while the rather than showing electrons moving through the wire, the animation will show the direction second number indicates the vertical location (away from the wire). Note the of positive charge flow. According to the right hand rule, if you place the thumb of your magnetic field value. Now move the sensor to the left and right, always leaving it right hand in the direction that the current is flowing, your fingers should curl around the Icm away from the wire. Is there any change in field when you do this? What would wire in the direction of the magnetic field lines. Check that this is true. Click the arrow to you expect from equation 1? reverse the current flow, and try it again. b. Return the magnetic field sensor to (1,1). Write down the value for B. (We will call 3. Click the box labeled "Grid" and the box labeled "Field Strength". The box at the top right this B1) Note that the units for magnetic field on this sensor is micro Tesla rather than should now show the magnitude of the magnetic field at the location labeled + on the Tesla, since one Tesla is a huge magnetic field. magnetic field sensor." rnier MAGNETIC FIELD A positive field value means that the c. Pull the field meter one more grid space to up to (1,2), and record the value for B, we magnetic field is out of the plane, and a negative value means that it is into the plane. will call this B2. 5d. Pull the field meter TWO more grid spacings to the up, so that it now lies at (1,4). We will call this B4. e. What is the ratio of Bi:B2 rounded to the closest integer? - 1 + f. What is the ratio of B2:B4 rounded to the closest integer? g. What is the ration of B1:B4 rounded to the closest integer? voltage - + h. From the values in steps e-g, what do you deduce is the relationship between magnetic field and distance? Does this agree with equation 1? N S My 6. Now we will determine the current dependence of the magnetic field. Move the field sensor to (4,4). Click the down arrow in the current box to reduce the current to zero, and record the magnetic field in the table below. Then click the up arrow, recording the magnetic field for each current reading Table 1: Magnetic Field Dependence on Current Current (1) Field (uT) 0 1.6 Field lines IN S 2.4 3.3 4.2 Faraday's Law PhET.= 5.5 6.1 Note: the voltmeter reads zero volts when the blue needle is pointing straight up. When the 6.9 7.8 needle deflects to the right, the voltage is positive. When it deflects to the left, the voltage is 8.7 negative. Move the bar magnet around the screen and observe what happens to the needle on the voltmeter. 7. Copy these data into a graphing program such as Excel, and plot Field (y axis) versus Voltage (x axis). How would you describe the relationship between Field and current? Is this 1. What voltage does the meter display when the bar magnet is stationary? Why? 2. Pull the magnet toward the loop. What direction does the needle move? Why? what you expect from equation 1? 3. Pull the magnet away from the loop. What direction does the needle move? Why? Part 3: Faraday's Law and Lenz's Law 4. Use Lenz's law and the right hand rule to predict which way you would expect the current to flow in cases 2 and 3. Make sure that you can justify your observations from 1-3. The purpose of this part of the experiment is to verify both Faraday's and Lenz's Laws, i.e. a) 5. Vary the speed with which you pull the magnet back and forth. How does the size of the The magnitude of the voltage induced depends on the rate of change of magnetic flux and b) The voltage induced depend on the speed? Why? direction of the induced voltage is such as to oppose the induced flux. We will verify each of these by following several steps. Click to reverse the bar magnet so that its south pole is now closest to the loop, Go to https://phet.colorado.edu/en/simulation/faradays-law You will see the following and repeat steps 1 to 5. What do you notice? 7. Flip the magnet polarity back to its original position. Click to bring up a second coil with two loops in addition to the coil with four loops. Pull the magnet back and forth in the two loops. Does the magnitude of the induced voltage seem to depend on the number of 6loops? Why or why not? (note: you will have to try to be consistent with the speed at which 1. Click on the red words "Time" in the top left corner to start the loop rotating. Watch the you pull the magnet back and forth. Look for the MAXIMUM deflection of the needle for a blue curve for flux and the red curve for emf in the graph below the magnet. How is the given setting to compare) loop oriented when the flux is at its maximum? How is it oriented when the emf is largest? Note the largest value for the emf. Part 4: Electricity Generation 2. Click "Time" again to reset, and vary the rotation rate. How is the maximum voltage Now we will look at the generation of electrical energy by rotating a coil in a magnetic field. The generated dependent on the rotation rate? Repeat for several values. basic idea behind a electrical generator is that a rotating magnet generates a changing magnetic Click "Time" again to reset, and vary the magnetic field. How is the maximum voltage flux that will induce an alternating electric voltage (emf) and current in a coil placed near the generated dependent on the magnetic field? Repeat for several values. magnet. The faster the magnet rotates, the faster the rate of change of flux, and thus the larger Click "Time" again to reset, and vary the area of the loop by changing the length and the electric current. The emf generated will be a sine function with one complete cycle for each depth. How is the maximum voltage generated dependent on the loop area (area = length rotation of the magnet. x depth)? Repeat for several values. 5. Try to explain your observations in 1-4 using Faraday's law. Load the following page and hit "Begin" You will see a page as shown below: http:/www.thephysicsaviary.com/Physics/Programs/Labs/SpinningCoilwGraphLab/index.html Part 5 Forces in Magnetic Fields: Static and Induced Currents Flux in Spinning Coil with Graphs Lab 1 9: 1.137 Mb Static Currents: Click on the link below to watch a video demonstrating the forces on currents in a magnetic field. https://www.youtube.com/watch?v=no9D8by-_CM . When the direction of the switch is reversed, the direction of the current is reversed. What happens to the direction of the force? 2. The Swing: Click on the link below, to load an animation of a standard lecture demonstration of a wire swing suspended in a magnetic field. When current flows in the horizontal wire of the swing, a force acts on it, deflecting the swing. http://www.walter-fendt.de/html5/phen/lorentzforce_en.htm On / Off Reverse current Turn magnet Current direction V Magnetic field You can click on any of the items in red script below the magnet to change them: length and Lorentz force depth vary the area of the loop, angle rotates it, B changes the magnetic field, and @ changes the rotation rate. W. Fendt 1998 8 9Click the orange button to toggle the current on and off, and notice the direction that the swing is deected. Check that the direction agrees with the right hand rule (ngers along current in the horizontal portion of the wire, bend in direction of eld, thumb points in direction of force). Repeat with the current in the opposite direction. What happens if you ip the magnet? . Induced Currents: When a conductor moves in a region of changing magnetic eld, Faraday's laws tell us that currents are induced inside it. These currents circulate in loops inside the conductor, and are thus called \"eddy currents\". This eddy current causes a magnetic eld which interacts with the external magnetic eld. This interaction causes forces which can seem to counteract the laws of gravity and energy conservation If the conductor has slits cut into it, the eddy currents can not ow as well, and thus there is less interaction between the conductor and the external mayJet. Below are several links to videos demonstrating this effect. Watch the videos, and be prepared to answer questions about what you see. httpszllwwwiyoutube. com/watch?v=L5vdLrnY-ch - What is the difference between the behavior of the ring with a break in it, and the complete ring? - What is the difference between behavior of the solid disk and the complete ring? hpszllwwwyoutube.com/watch?v=CQSahg law 0 What causes the ring to jump? httpsz/lwwwiyoutubei coanatch7v=aL2hedsE 261 0 Which pendulum slowed down faster: the solid copper or the copper with the slits in it? Why? hps://www.utube. com/watch?v=ncUOlIE9nga4 What is causing the magnet to levitate? Is the plate below it magnetic? . A demonstration of a Lenz's Law involves a tube through which a magnetic pellets is dropped. One tube is conducting, the other is not As the magnetized pellet falls, a merit is 10 induced in the walls of the conducting tube, but not in the Walls of the insulating tube The direction of the current may be determined by applying Lenz's law. The magnetic eld that accompanies the induced current will oppose the change in the magnetic ux as the pellet passes through. The current induced below the pellet will have an accompanying magnetic eld which opposes the increase in the magnetic ux brought about by the approaching pellet. The current above the pellet will have an accompanying magnetic eld which opposes the decreasing magnetic ux as the pellet moves away from this part of the tube. This counteracts the force of gravity, and makes the pellet fall more slowly. This effect is shown by the two videos below. ht_tps://www.youtube.corn/watch? 16XtJ6vELU hnps://www.youtube.com/watch?v=N7tli71 -AjA o Why is the magnet's fall slowed down in the copper and aluminum tubes, but not in the glass tube? 0 Make a sketch of the pellet passing through a section of tube. Draw the eld lines surrounding the pellet and determine the direction of the induced current below the pellet and also above the pellet (they will be opposite). (MIT Department of Physics Technical Services Group. \"518-003 Physics Demonstration Videos, Spring 2012, (MIT OpenCourseWarc: Massachusetts Institute of Technology). hlgp:[locw.mit.edmresomes/res-lE-OOS- physicsdemonstmonvideos-gringZO12 (Accessed 1 Nov, 2013). License: Creative Commons BY-NC-SA) 11