Online-Lab-8_Electromagnetic-Induction (1)

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PHYS 1402 Lab 8: Electromagnetic Induction Name: _____________________ Objectives  To observe the force exerted on a current carrying wire in a magnetic field.  To discover under what circumstances a magnetic field can induce a voltage in a coil of wire.  To relate the voltage and current induced in a coil of wire to the rate of change of magnetic flux passing through it.  To verify Faraday’s law of electromagnetic induction.  To verify Lenz’s law of electromagnetic induction. Marketable Skills: This course assesses the following Core Objectives. In this assignment, you will develop the following marketable skills: Critical Thinking  Analyze Issues  Anticipate problems, solutions, and consequences.  Apply knowledge to make decisions  Detect patterns/themes/underlying principles  Interpret data and synthesize information Communication  Summarize information  Use proper technical writing skills Personal Responsibility  Accept responsibility  Exhibit Time Management  Show attention to detail  Learn and grow from mistakes Empirical Quantitative  Communicate results using tables, charts, graphs  Contextualize numeric information/data  Demonstrate logical thinking  Draw inferences from data, use data to formulate conclusions  Use appropriate calculations to solve problems 1

Overview You will explore three phenomena in this lab: (1) the magnetic force exerted on a long straight current-carrying wire; (2) Faraday’s law of electromagnetic induction that describes how changing magnetic fields produce electric fields, emfs, and currents; and (3) Lenz’s law that describes the sense or direction of the emfs and currents produced by electromagnetic induction. Activity 1: Magnetic Force on Current-Carrying Wires Next, we will examine the effects of a magnetic field on a wire. You will watch the following video: https://dcccd.yuja.com/V/Video?v=988351&node=3897462&a=1186250782&autoplay=1 The switch is turned on and the current carrying wire is placed parallel to the magnetic poles. Question 1: Describe your observations. Question 2: If there is a force on the wire, note the direction of the force relative to the direction of the magnetic field. The switch is turned off. Magnet is rotated such that the current-carrying wire lies between the poles of the magnet. Question 3: What happens when there is a current flowing in the wire? Describe your observations. Question 4: If there is a force on the wire, note the direction of the force relative to the direction of the magnetic field and the current. Question 5: What happened when the current was reversed? Activity 2: Magnetic Field Download and run the simulation “Faraday’s Electromagnetic Lab”: https://phet.colorado.edu/sims/cheerpj/faraday/latest/faraday.html?simulation=faraday 2

Step 1: Notice the magnetic field lines, how they originate from the north pole and end on the south pole. Drag the compass around at different places near the magnet and notice the direction of the magnetic field there. Click on flip polarity and notice how the magnetic field lines change direction when the north pole becomes south and vice versa. Step 2: Move the compass to the side away from the bar magnet. Check the box next to “Show Field Sensor”. A magnetic field sensor will appear, displaying the average magnetic field B at that point where it is placed, along with the horizontal and vertical components B x and B y as well as the direction of the field vector relative to the bar magnet. Step 3: Drag the Field Meter with its cross hair at point A shown in the picture below. Record the magnetic field along with directions at this point, writing all values in the table on the next page. Step 4: Repeat Step 3 for points B, C, D, E, and F 3

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Point B (G) Bx (G) By (G) q (Degrees) A B C D E F G Question-6: Based on your data table, where is the magnetic field strongest? Question-7: Based on your data table, where is the magnetic field weakest? Activity 3: Interactions between a magnet and a coil Step 5: Click on the tab “Electromagnet” on the menu bar on top of the simulation. You will see that a coil is connected to a battery, and as the current passes through the coil, there is magnetic field produced near the coil. Inside the coil the magnetic field is almost constant and parallel to the axis of the coil. Step 6: Check the “Show Field Meter” box. Place the Field Meter somewhere near the coil. Slowly decrease the battery voltage by sliding the horizontal bar on the battery. Notice that as the current decreases the magnetic field also decreases in strength. Question-8: What happens to the magnetic field when you reverse the direction of current by sliding the battery voltage bar past 0 volts. Step 7: Keeping the Field Meter at the same place, click on the AC under the Current Source menus. Question-9: What kind of magnetic field do you see now? Why is it constantly changing? Step 8: Click on the tab “Pickup Coil” on the menu bar on top of the simulation. You will see that a coil is connected to a light bulb without any battery in the circuit, and the light bulb is off. Drag the bar magnet and slowly move it through the coil, you will notice that bulb light up while you are moving the magnet and stops lighting when you stop the magnet or if the magnet is far away from the coil. Keep the magnet fixed at one place and move the coil such that coil goes over the magnet and notice that the light bulb again lights up. So, it does not matter if you move the magnet or the coil, in both cases you are producing electricity. All our modern electricity production industry is based on this simple principle that when a magnet moves near coil (or 4

vice versa), it produces electricity in the coil. This is called Faraday’s law of electromagnetic induction, discovered independently by Michael Faraday in 1831 and Joseph Henry in 1832. Now move the magnet faster and notice the brightness of the light bulb. Question-10: Does the brightness increase or decrease? Step 9: Under the Pickup Coil menu, click on the “Voltage Indicator” and set the number of loops to 1. Now move the magnet through the single loop coil as fast as you can a few times and notice how high the Voltage indicator goes. Change the number of loops to 2, and again move the magnet as fast as you can, looking at the Voltage Indicator. Repeat this process with 3 loops too. Question-11: Does the voltage (or emf) induced increase or decrease with a greater number of loops? Step 10: Keeping the number of loops fixed, increase, and decrease the area of the coil using the horizontal bar under the Pickup Coil” menu. Question-12: Does the induced emf or voltage increase or decrease when you decrease the area of the coil? Step 11: Remember that in Step 5 we found out that when electric current runs through a coil, the coil becomes a magnet, and we studied its magnetic field. That means that if current runs through a coil, we can move it near another coil and induce a current in the secondary coil (the apnea monitors used in the hospitals to monitor patient breathing patterns work on this principal and essentially consist of two coils). Let’s test this idea. Click on the tab “Transformer” on the menu bar on top of the simulation. Move the coil connected to the battery near the coil connected to the light bulb quickly and you will notice that the bulb lights up, so emf is indeed induced as we expected. Instead of moving the coil connected to the battery you can move the coil connected to the light too, and you will get the same induced emf. Step 12: Now bring the coil connected to the battery and place it close to the other coil connected to the light bulb. Once you leave it there you will notice that the bulb is not lit up anymore. Of course, you are not doing the work, hence there is no voltage induced. You must continuously do the work to get the induced voltage. Why? Because you can include the voltage only by changing magnetic flux, you need to move the magnet to achieve that. Step 13: Keeping the coils where they were in Step 12 (light bulb off), click on AC under the Current Source menu to run the AC current through the coil that was initially connected to a DC battery. Notice that the light bulb now continuously turns on and off, so voltage is induced but it is AC, it goes to a maximum and a minimum. You can see that the magnetic field is continuously changing not only in magnitude but also it flips its direction, so the magnetic flux is continuously changing. If you increase the number of loops in the coil that is connected to the 5

light bulb, you will observe that the light bulb gets brighter, so more voltage is induced. That is how transformers work, if you want more voltage, you will increase the number of loops of the secondary coil. Question-13: How would you explain the fact that now you are not doing any work and still a voltage is induced? Who is doing the work now? Step 14: Now that we know that moving a magnet near a coil induces a voltage in the coil, but the moment you stop moving the magnet the induced voltage drops to zero. You may ask that how we produce electricity then, that keeps running all electric devices in our homes and office all the time. The answer is we use an electric generator that utilizes Faraday’s law of electromagnetic induction. Let’s look at an electric generator now. Click on the tab “Generator” on the menu bar on top of the simulation. Under the Pickup Coil menu, click on the “Voltage Indicator” and set the number of loops to 1. Turn on the water tap by slowly sliding the horizontal bar on the faucet. As the water falls onto the wheel, it starts rotating, the magnet attached to the wheel also rotates, changing magnetic flux through the coil placed next to it, inducing an emf in the coil. Question-14: Try all the different settings in this simulation and find out at least 4 different variables that increase the induced voltage . 6

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