NSF-GK12 Program at Chelsea High School

Physics, Electrostatic

10-12

Concept of electrostatic forces, Coulombs law, and mechanics (sum of the torques about a point of a static object is zero)

The students will observe the effect of electrostatic force between two charged pieces of tape, learn how to calculate the magnitude of this force and the number of electrons transferred between objects.

The purpose of this lab is to illustrate the existence of electrostatic force between two charged objects (pieces of tape) and methods of finding the direction and magnitude of this force.

1. Scotch tape
2. Rulers
3. Digital scale

Cut two pieces of tape each 6cm long.  Make a place to grip by folding the 0.5cm end of each piece (see picture). Ask the student to predict what will happen if you hold them back to back (non-sticky side) on one end only (see picture).  Let them brainstorm and collect their answers.  Now, demonstrate it to the class. The tapes should be parallel with each other with a very small separation between them. Ask students to justify their observations.

Next, stick the tapes on the table, rub on them, and peel them off.  (Note: when want to peel off the tapes, grab the gripper and apply a perpendicular force to the surface of the table.  With this method of peeling, the tapes do not curl.)  Now, ask the student to predict what will happen if you hold them back to back again. Demonstrate it to the class.  Now the pieces of the tape should repel each other and make an angle on top with a big separation on the bottom ends (see picture).  Ask students to explain their observation.  Guide the class discussion by asking student think about what is different between the first and second demos.  What was different in the procedure?  Guide the class discussion towards the transfer of electrons from the table to the tapes.  Ask students what kind of charge each piece of tape has and why.  Do alike charges attract or repel each other? Ask the students what causes the separation between the tapes.  Arrive to the conclusion that this is the electrostatic repelling forces that cause the tapes to separate.  Ask students if the number of electrons transferred to each tape can be calculated.  Tell them that they will find out when they complete the lab.

Break the class in to groups of two and have students repeat the experiment.  Have them measure and record and lengths of each piece of tape and the distance between the bottoms of the tapes when they repel each other using a ruler.  Also have the students measure the mass of each piece of the tape using a digital scale.

Have students complete this lab sheet.

Conclusion:

Electrons transfer between objects.  There is an electrostatic force between charged objects.  Alike charges repel and alike charges attract. A rough estimate of number of transferred electrons can be calculated given that the objects have the same charge.

Collect the lab sheets and evaluate.