Name: ___________________________________
Date: ____________________________________

PITH BALL ELECTROSCOPE LAB


Purpose: To use a pith ball electroscope to determine charges.

Materials and Methods:

  1. Bring a negatively charged ebonite rod close to (don't touch) the uncharged pith ball, and then remove it.

  2. Repeat step 1 with a positively charged glass rod.

  3. TOUCH the uncharged pith ball with a charged ebonite rod, remove the rod, and then slowly APPROACH (don't touch) with the same charged ebonite rod. Now APPROACH (don't touch) with a charged glass rod.

  4. Gently touch the pith ball with your fingers to "ground" (discharge) it.

  5. TOUCH the uncharged pith ball with a charged glass rod, remove the rod, and then APPROACH (don't touch) with the same charged glass rod. Now APPROACH (don't touch) with a charged ebonite rod.

Observations:

step 1

 
step 2

 
step 3

 
step 5

 


Questions: (Answer on a separate sheet)

  1. Draw a neat, well-labelled diagram (in pencil) to illustrate each of the following. In each diagram, label the pithball electroscope, fur or plastic, ebonite rod, positive and negative charges that do or don't move, any movement of pith ball.

    2. a)How to charge an ebonite rod negatively.
    b)How to charge a pith ball electroscope negatively with an ebonite rod.
    c)How the pith ball electroscope reacts to an ebonite rod after both have been charged negatively and the rod is brought close.

  2. What charge is transferred to the pith ball when an ebonite rod rubbed with fur is touched to it? How do you know the charge you indicated was transferred (ie. think of how the pith ball reacts when the rod is brought near it after contact). Are electrons moving from the rod to the pith ball or from the pith ball to the rod?

  3. What charge is transferred to the pith ball when a glass rod rubbed with plastic is touched to it? How do you know the charge you indicated was transferred (ie. think of how the pith ball reacts when the rod is brought near it after contact). Are electrons moving from the rod to the pith ball or from the pith ball to the rod?

  4. Define the "Law of Attraction and Repulsion" (pg. 301).

  5. In step 4 you "grounded" the pith ball electroscope by touching it with your fingers. Read the section on GROUNDING in your text and briefly explain the process (pp. 311-312).