Question

Lab’s goal

To investigate the electrostatic interaction between various objects.

Theory

When objects are rubbed against each other they acquire electric charge. Objects of the same electric charge repel and objects of opposite charges attract.

Different materials have different “desire” for electrons; this is called electronegativity.    Some materials will always steal electrons from things they come in contact with; others are more willing to give up electrons.

Procedure

Activity 1: Determine how different objects interact through the electrostatic force.Top of Form

1. Cut 4 pieces about 10-cm-long scotch tape. Fold one end to prevent it from sticking.
2. Stick two pieces directly onto a smooth surface. Write "X" on the folded end (both pieces are stuck on the table surface.)
3. Stick the third tape on the table as well. Write "B" on its folded end.
4. Stick the fourth tape (cut it less than 15 cm) on top of the "B" tape. Write "T" on its folded end.

Determine the interaction between the various scotch tapes, and various objects.

1) Pull the two "X" pieces off the top of the table. Bring them close to each other.
Do they repel or attract each other? __They repel each other_____________________________________
Does it matter which side faces which side? ­­­­­­­­­­­­­­­___The side is irrelevant______________________

2) Pull the "T" and "B" pieces off the table together. Using both hands, separate the tapes abruptly. Bring them close to each other.
Do they repel or attract each other? ____They attract each other___________________________________
Does it matter which side faces which side? __The side is irrelevant______________________________

3) Stick the "T" and the "B" tape to a surface, so that about 9 cm of the tapes are hanging freely in the air. Make sure the tapes are sufficiently far so that they do not interfere with each other. At any time if you notice the tapes are beginning to lose their charge, you can recharge them by repeating the preliminary set-up.

4) For each of the following objects, determine whether they are repelled or attracted by tape "B" and tape "T". Record your data in your data table.

• Another "T" tape.
• Another "B" tape.
• "X" tape.
• Plastic rubbed with wool.
• Wood rubbed with wool.
• Glass rubbed with silk.
• A metal sphere.
• A paper sheet.
• Human hand

Record your data in the following table. Write down "attract" or "repel" according to your observations.

Object	“T” tape	“B” tape
"T" tape	repel	attract
"B" tape	attract	repel
"X" tape	attract	repel
plastic rubbed with wool	repel	attract
plastic rubbed with cotton	repel	attract
wool rubbed onto plastic	repel	attract
wood rubbed with wool	attract	repel
glass rubbed with silk	repel	attract
metal sphere	attract	repel
paper sheet	repel	attract
human hand	attract	repel

Results.

Arrange the objects in two categories according to their charge.

"T" charge		"B" charge

What is the charge of the metal sphere? ____________________________________

What is the charge of your hand? __________________________________________

Answer 1

Arranging the two objects into categories according to their charge is fairly easy because there are only two possible scenarios. And like charges repel each other. That means, the objects repelling each other are having the same charge.

T Charge	B Charge
Plastic Rubbed With Wool	"X" tape
Plastic Rubbed With Cotton	Wood Rubbed With Wool
Wool Rubbed Onto Plastic	Metal Sphere
Glass Rubbed With Silk	Human Hand
Paper Sheet

Charge on metal sphere and human hand is the same because they are both repelled by the "B" Tape. The name positive or negative charge is mere convention. Traditionally, when glass is rubbed with silk, the rod looses electrons, and becomes positively charged, and silk picks up those electrons and become negatively charged. Since Glass rubbed with silk is "T" Charge, and by our tradition convention, it is positive. Hence the metal sphere, and human hand are negatively charged.
Please note that positive and negative are just conventions introduced by us. What we call positive can very well be called negative and vice versa.

Charge on metal sphere, and hand is "B" Charge, and from our convention, negatively charged.