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USE A3 Video Clip 1: Class discussion of Initial Ideas
Three groups present their model representations for an uncharged electroscope. Group 1 has a distribution of equal numbers of + and – charges while Group 3 does not show any charges because they are concerned that any representation of + and – charges will imply that there are locally charged regions on an uncharged object. At the end Group 6 presents an alternative representation that pairs charges together.
USE A3 Video Clip 2: Group 3 works on STEP 1 of Exploration #1
Group 3 discusses whether they think the tinsel on an uncharged soda-can electroscope will become charged if a positively charged acrylic sheet is brought close to the other end. They decide that it will become charged because positive charges will jump from the acrylic to the electroscope.
USE A3 Video Clip 3: Group 3 continues working on STEP 1 of Exploration #1
The group watches the video of the positively charged acrylic sheet being brought close to the base end of the uncharged electroscope. They see that the tinsel becomes more spread out but also decide that it does not go back to its previous state when the acrylic is removed. They take this as supporting their previous idea about some charge being transferred from the acrylic to the electroscope.
USE A3 Video Clip 4: Group 3 works on STEP 2 of Exploration #1
The group discusses how to explain the behavior of the electroscope using their model in which they assume charges are transferred from the acrylic sheet to the electroscope. April proposes an explanation in which the transferred charges produce a 'domino effect' that results in positive charges being pushed into the tinsel thus making it positively charged.
USE A3 Video Clip 5: Group 3 works on STEP 3 of Exploration #1
[Poor audio quality!] The group discusses the predictions in STEP 3. They first decide that because the tinsel is now positively charged it will be repelled by a second charged acrylic sheet. They also decide that when a negatively charged Styrofoam© plate is held nearby it will cancel out the effect of the first positively charged acrylic and so the tinsel will show no reaction. Next they decide that according to their model the base end of the electroscope should remain uncharged because the transferred positive charges simply take the place of charges that were there previously. Finally since charges were transferred they decide the acrylic sheet would have less charge than before.
USE A3 Video Clip 6: Group 3 works on STEPS 4 & 5 of Exploration #1
[Poor audio quality!] The group watches the movie of a simulator and notices that in this the base end of the electroscope becomes negatively charged which does not agree with their prediction. April then proposes an alternate explanation in which the charges in the electroscope move around but no charge is transferred from the acrylic.
USE A3 Video Clip 7: Group 3 works on Exploration #2
[Poor audio quality!] Having now developed an explanation that is consistent with the evidence they saw in Exploration #1 the group quickly makes predictions for how the uncharged electroscope should behave when a negatively charged Styrofoam © plate is brought close to its base end. They watch a movie of the experiment that confirms their predictions.
USE A3 Video Clip 9: The class answers Summarizing Questions #2 and #3
Group 3 presents their model representations for S2. Following this a group off camera gives their reasoning why the tinsel falls back down when the charged object is removed (S3). The instructor prompts for ideas about a mechanism for this and Group 3 responds with an explanation based on repulsion of like charges.
USE A3 Video Clip 1: Class discussion of Initial Ideas