PURPOSE:
To expose the student to new equipment and lab procedures. And to test the electropositive - electronegative properties of different rods when rubbed with cotton.

INTRODUCTION:
An electroscope is a scientific instrument that is used to detect the presence and magnitude of electric charge on a body. The electroscope consists of a gold leaf attached parallel to a conductive center piece of metal. This conductive center is attached to a ball on top and positioned within a metal and glass box. The conductive center piece is insulated from the box. When a charged rod is brought near or touches the ball atop a neutral electroscope, the gold leaf rotates upward. The degree of rotation of the gold leaf can give an estimation of the magnitude of charge imparted to the electroscope. If the ball comes in contact with a grounded object, the gold leaf returns to its vertical position. Different types of rods will generate either a positive or negative charge when rubbed with different materials such as cotton, silk or nylon. During this lab you will observe the actions of an electroscope and determine if the provided rods generate a positive or negative charge when rubbed with cotton.

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The 7 different rods used in this lab are kept in a grounded rack. All charge is removed when the rods are placed in the rack.

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A stand is provided that will hold the cotton that will be used to impart a charge on the different rods. The rods must be rubbed back and fourth several times on the cotton in order to generate the maximum charge.

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If you get into trouble and perform some procedure that causes the lab to fail(lab equipment will no longer operate), you can press the "Reset" button and the simulation will return to the starting position.

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PROCEDURE:

1) You can adjust the background shading by clicking on the "Special" button to the right and selecting "Background". Click on the "Special" button and select "Print Blank Report" to obtain a web page that can be printed and used as a lab report. (the program will not be interrupted)

2) Drag the "grounding hand" over to the electroscope and touch the wad of steel wool, held by the hand, to the ball on top of the device. This will ground the electroscope and remove any charge. Move the hand away.

3) Pick up the glass rod and drag it over to the ball of cotton on the stand. Rub the rod on the cotton for several seconds. The more rubbing, the more charge (to a maximum). Drag the rod over to the electroscope and approach the ball BUT DO NOT TOUCH THE BALL WITH THE ROD! Observe what the gold leaf does as you move back and fourth near the ball. Record this observation under observations #1. This method of transferring charge is called "electrostatic induction".

4) Now move the rod over and actually touch the ball. Move the rod away. Record your observations of the gold leaf under observations #2. This method of transferring charge is called "electrostatic conduction".

NOTE: When a glass rod is rubbed with cotton, a positive charge is generated on the rod. Notice that the glass rod is listed as positive on your data sheet.

Rule: if the same charge is added to a charged electroscope, the gold leaf deflects even more from the conductive center rod (to a maximum).

Rule: if the opposite charge is added to a charged electroscope, the gold leaf deflects back towards the conductive center rod and may return to a vertical position.

5) From procedure step #4, the electroscope has a positive charge. Drag the "grounding hand" over to the electroscope and touch the wad of steel wool to the ball on top of the device. Record your observations under observation #3.

6) Charge the electroscope as before (procedure #3 and #4). Put the glass rod back in the rack and pick up the Lucite rod. Charge it with the cotton. Draw it near the electroscope ball and determine, using the two rules above, if its charge is positive or negative. Record. Return the rod to the rack and then ground the electroscope ball.

7) Repeat procedure #6 for the other 5 rods, recording if they charged positive or negative.

8) Answer the requested values asked for on the lab sheet and any given by your teacher. Select "File Report" to send a copy to be viewed by your teacher.