Voltage and Current Lab

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Name:Section: SP1L-17Date: 2/26/11

Coulomb’s Law: What is the charge on a charged pith ball?

Experimental Determination of the Electrostatic Force acting between two charged pith balls

Equipment: a pvc pipe and fur or wool, a metric ruler, a protractor, two pith balls on a stand as in figure 1. Your teacher will tell you the mass of your pith balls.

Procedure: Make sure the strings of your two pith balls are untangled as in figure 1. Make sure that the pith balls are neutral by rubbing them with your finger. Measure the length from the point that the strings can pivot on the stand to the center of the ball and record it. Charge the pith balls according to the instructions given by your lab teacher. When the pith balls are fully charged alike (negative) they will noticeable repel each other.

figure 1 figure 2

[pic] [pic]

Use the protractor to measure the angle between the two strings.

|Length of the strings, (l) |Angle between the strings, (θ) | |0.18 m |8 degrees |

When the pith balls have reached their final charged position and are at rest, what do we know about the forces acting on them?

Name the force: AB C

To determine the electrostatic force, label the vector diagram below of the forces acting on the pith ball.

1. Using your vector diagram above, determine the ratio of Fe to Fg in terms of θ/2.

2. Write an equation for the electrostatic force on the pith ball in terms of angle Ѳ/2 and the weight of the pith ball.

3. Calculate r/2 (half the distance between the two charged pith balls) using the length (l) and the angle Ѳ/2. Then double it to find r. Show your work.

4. Set the equation for Fe written in 2. equal to...
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