Use video experiments to devise and test a rule for the direction of the induced current through a coil that is not connected to a battery. I. OBSERVATIONAL EXPERIMENT: HOW TO INDUCE A CURRENT IN A COIL NOT CONNECTED TO A BATTERY The goal of this experiment is to observe 2 sets of videos to find a pattern for the conditions under which there is a current through a coil of wire that is not connected to a battery. Available equipment: Computer with internet connection a) First, make sure you know what a galvanometer is. A galvanometer is a device that registers electric current through it. It has a coil connected to an arrow with a spring, and a magnet (look at the photo below to identify these elements). When the current flows through the coil, the magnet exerts a torque on it and the coils starts turning pulling on the spring. The spring exerts an opposite torque on the coil. When these two torques are equal in magnitude, the coil stops rotating and the arrow attached to it shows a reading on the scale. The larger the current, the more force the magnet exerts on the coil, the greater the magnetic torque, the larger deflection of the arrow. As the current can flow in two directions, the scale of the galvanometer is set up with the zero 3 in the middle, so that the needle can deflect to the right and to the left. Watch this video to see a galvanometer being calibrated. b) Watch this video of someone moving a magnet near a coil of wire connected to a galvanometer and this video of a coil of wire connected to a galvanometer moving near a permanent magnet. 1. Record your observations il. How many patterns can you identify in each video? List each of these patterns. iil. Are these patterns the same in both videos or there is a difference? c) Using the patterns in both experiments devise a preliminary rule that summarizes the condition(s) needed to induce a current in a coil. Write that rule in your report d) Examine the experiments listed in the table on the next page. Is the rule you devised consistent with the outcomes of these experiments? Explain.

Experiment # Written Description Illustration of Outcome Hold the magnet motionless in front of the coil, with any orientation. Hold the magnet perpendicular to the coil with 2 the N pole facing the coil. Move the magnet IN N T quickly toward the coil. Then pull it away quickly. 3 Repeat experiment 2, but this time with the S S N pole facing the coil. Align the magnet in the same plane as the coil 4 and move either pole toward or away from the coil. Hold the magnet in front of the coil and rotate it N S 5 90" as shown. (The magnet starts out perpendicular to the coil and ends up parallel to it.) Position the magnet as in experiment 2, but this IN SN 6 time grasp the sides of the coil and collapse the coil quickly. Then pull it back open. A

II. TESTING EXPERIMENT: IS MOTION NECESSARY FOR INDUCING ELECTRIC CURRENT IN A COIL NOT CONNECTED TO A BATTERY? The goal of this experiment to test the rule you invented in Experiment I. Available equipment: Computer with internet connection a) In this experiment you have two coils: one (coil A on the left) connected to a large galvanometer and one (coil B on the right) connected to a power supply and current indicator (another small galvanometer). Use the rule you invented in Experiment I to predict what happens to the reading of the galvanometer connected to coil when two coils are positioned next to each other as shown in the photo below. For each prediction, be as specific as you can. Sketch a rough / vs. t graph for what you think the galvanometer will show. Experiment # Written Description Prediction Based on Rule Outcome Coil B is moved away from coil A, then moved back. 2 Coil A is moved away from coil B, then moved back. 3 Coil B is moved perpendicularly away from coil A, then moved back into place. 4 Coil B is suddenly disconnected from its power supply, then reconnected after a few seconds.

b) Once you have made your predictions watch this video and record the outcome of each experiment. Be as specific as you can in recording the outcomes. c) Did the outcomes of the experiments match your predictions? If not, how should you revise your rule?

III. OBSERVATIONAL EXPERIMENT: WHAT AFFECTS THE DIRECTION OF THE INDUCED CURRENT? The goal of this experiment is to decide what factors affect the direction of the induced current. Available equipment: computer with internet connection. a) The six experiments shown in the table below are like experiments conducted earlier using a bar magnet, a loop of wire, and a galvanometer. The only different is that now the direction of the induced current is shown. Experiments -V Lind S v Iind S N N 25 N S S Coil area is collapsing Coil area is expanding b) Use the data in your notes to devise a rule relating the direction of the induced current in the coil and the change of external magnetic flux through it. Hints: (1) Focus on the direction in which Bext is changing rather than the direction of Bext itself. (2) Compare the direction of the induced magnetic field vectors B through the middle of the loop to AB ext. c) Formulate a general rule: How does the direction of the induced current in a coil relate to the change of external magnetic flux through it? d) Watch this video and whether the rule you created is consistent with the outcomes of the experiments in the video. Provide the details from the video to support your argument.

Write a report describing what you did in Experiment II. This report should include the following, and should be understandable by someone who did not attend lab: 0 A brief summary, in your own words, of the purpose of the experiment. What were you trying to accomplish? Clearly state the hypothesis that was being tested. 0 A table with the predictions you made for each experiment with an explanation of how each prediction was reached from the hypothesis. 0 The outcomes of all experiments. 0 Your judgment about your hypothesis and any changes that needed to be made to it.

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