Fun with Tape! Discuss with your group: what you know about electrical charges? Summarize the keys ideas below.

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1 Fun with Tape! Name: Group: NOTE: All the activities involving Scotch tape requires properly charged tape. After you peel the tape off, handle it carefully. Try not to touch them with other objects, especially metal objects. For easier handling, fold the sticky side of the tape onto itself on one end of the tape. When bringing two pieces of tapes together, do so with the non sticky sides facing each other, NOT the sticky sides. Otherwise, the investigation could be flawed and might lead to wrong conclusions. Discuss with your group: what you know about electrical charges? Summarize the keys ideas below. Charging objects Go to Phet.colorado.edu. Open the PhET SIM John Travoltage. Rub John s foot on the carpet. Describe what happened. What do the blue spheres represent? What happens when John touches the door knob after he rubbed his foot on the carpet multiple times? 1

2 Investigations Obtain a piece of Scotch tape (~ 10 cm). Press it firmly on a smooth unpainted surface (like the table). Peel the tape off quickly. Describe the behavior of the tape as you bring something (your finger, a pen, etc.) toward it. Take care not to let the tape make contact with the object. Make another piece of tape as described above. Bring the second piece of tape toward the first one. Record your observations. How does the distance between the tapes affect their interaction? Each member of your group should press a piece of tape onto the surface and write a B (for bottom ) on it. Then press another piece of tape ON TOP OF each B tape and write a T (for top ) on it. Slowly pull each pair of tapes off the table together. After they are off the table, separate the T tape and the B tape quickly. Describe the interactions between the following items when they are brought near each other. two T tapes two B tapes a T and a B tape a T tape and little bits of paper (tear bits off of paper towel. Smaller bits, 2 mm or smaller, work better) a B tape and little bits of paper two small bits of paper 2

3 Just like John became electrically charged when his foot is rubbed on the carpet, a piece of tape becomes electrically charged when it is rubbed against the table and peeled off. Small bits of paper, on the other hand, are considered neutral. Is neutral a type of charge? Justify your answer either way. No. Neutral is when there are equal number of positive and negative charges so that the object has no net electrical charge. Based on your observation on the previous page, describe a procedure, using T tape and B tape, that you could use to determine if an unknown object is charged or neutral. Prepare a T tape and a B tape (or two objects, one with positive charge, on with negative charge) If an object attracts one tape and repels the other, it is charged; If an object attracts both tapes, it is neutral. Make a fresh set of T tape and B tape. Rub a PVC pipe with a piece of cloth. Hold the pipe near the newly made T and B tapes. Record the observations. Determine whether the pipe is charged or neutral. If it is charged, does it has the same change as T tape or the same charge as B tape? Justify your answer. 3

4 Visual Model Go to Phet.colorado.edu. Open the simulation, Balloons and Static Electricity. Examine the sweater, the balloon and the wall (on the right). Do each of them contain electrical charges? How do you know? Do the sweater, balloon and the wall contain any net charge at this point? How do you know? Grab the balloon and rub it against the sweater. Return the balloon to its original position. What happens? Grab the balloon and touch it against the wall on the right. What happens? Pay attention to details. Compare the interactions between the sweater, the balloon and the wall with the interactions between the T tape, the B tape and small paper bits. Try to match them up one on one. Justify your answer. If it s impossible to match the items up exactly, explain why. Sweater paper bit Wall behaves most like paper bits as a neutral object Balloon B tape Balloon and sweater are like the T tape and B tape Wall T tape However, at this point, it is not possible to identify which tape has the positive charge and which tape has the negative charge. We just know that the two tape have opposite charges. Try to draw a diagram showing the charges on a piece of T tape, B tape and a piece of paper bit, respectively. 4

5 Identifying charge Obtain two flexible straws and stick each into a small piece of Play Doh to form inverted L s. These will serve as holders for a freshly made T tapes and B tapes. T This activity requires finesse and care. If you make sure your T tape and B tape always have a good charge, the activity should go smoothly. Obtain a set of the objects listed in the table below. Try rubbing each object with a piece of cloth. First bring the object near a hanging strip of T tape then near hanging strip of B tape and finally near a small stack of paper bits. There are spaces provided for you to try a couple of objects of your own. Record your observations in the table below. Write attracted, repelled or neither. Items Bits of paper T tape B tape PVC pipe Plexiglas plastic silverware Wood tongue depressor glass test tube metal nail magnet Aluminum tube Paper clip What observation or observations would provide conclusive evidence that an object is NOT electrically charged? Explain. If an object is attracted by both T tape and B tape, it is NOT electrically charged. Or if an object has no interaction with bits of paper, it indicates that it is NOT electrically charged. Check with your instructor 5

6 Positive and Negative Charges The phenomenon you have just observed was first recorded by Thales of Miletus nearly 2500 years ago in ancient Greece. He observed that a piece of amber rubbed with fur attracted feathers and dry leaves. During the middle ages, it was noted that a glass rubbed with silk or cotton would behave similarly. It remained just an interesting phenomenon until ~1600 when Sir William Gilbert made the first systematic study of the phenomenon. He called the phenomenon 'electricity' after 'electron', the Greek word for amber. In 1747, Benjamin Franklin became America's first internationally known scientist after publishing his studies on electricity. Besides flying his kite in a thunderstorm, and inventing the lighting rod, Franklin was the first to name the two types of electricity plus and minus. Franklin named the kind of electricity found on glass after it had been rubbed with cloth plus or positive electricity. Even though some of Franklin's original ideas of electricity have now been replaced, people have continued calling the two types of electrical charge plus and minus (positive and negative). What happened when a piece of glass is rubbed with cloth that gives the glass its positive charges? Electrons move off of the glass, leaving behind excess positive charges and a net positive charge. Draw a diagram showing the net charge on a piece of glass after it is rubbed with cloth. showing net charge showing all charges Based on the interactions of the glass test tube with the T tape and B tape, determine the charge of the T tape and B tape. How did you decide this? T tape: positive charge because it is repelled by the glass test tube, which means it has the same charge as the rubbed glass B tape: negative charge because it is attracted by the glass test tube, which means it has the opposite charge as the rubbed glass. Now that you have identified the charges of your T tape and B tape, draw diagrams showing the charges on each tape. showing net charge Showing all charges Consider the fact that conductors have some free electrons that can easily move around within the metal. Draw a diagram of a metal nail with a piece of T tape held near. Indicate the net charges on the tape and the nail, illustrating why they attract each other. 6

7 Now determine the type of net electrical charge found on the objects in the table above. Items Positive, negative or neutral? PVC pipe Plexiglas plastic silverware Wood tongue depressor glass test tube metal nail magnet aluminum tube Paper clip Check with your instructor 7

8 Magnetism The magnets you are using are very strong, but they are brittle. Please take care not to break them! Examine and describe what you see on a bar magnet. Bring two bar magnets close to each other and examine their interactions. Try bringing different ends of the magnets together and record what happens. Test each item in the table above to see if they are attracted by the magnet. If there is a very weak attraction, it s probably not a magnetic force since these are very strong magnets. Which items are strongly attracted by the magnet? Did any of the items that are not strongly attracted surprise you? Based on your observations, are magnets attracted to electrical charges? Justify your answer. 8