# Lab: Determining the Charge on a Pith-Ball

Topics: Electric charge, Electrostatics, Electric field Pages: 4 (791 words) Published: September 23, 2013
﻿Riley Jefferson
Block 7/8
October 8th 2012
Electrostatic Gedanken Lab
Group Gamma

Objective: The objective of this lab is to determine the charge on a pith ball.

Hypothesis: I fully believe that the charge of the pith ball will be positive. The formula I will use to prove this is Coulomb’s Law, (Fe=(k*q1*q2) / r²). ‘Fe’ is equal to the electrostatic force between the spheres, measured in Newton’s. It is also a vector quantity, and it’s in absolute value. Secondly, ‘k’ is equal to Coulomb’s law constant. The constant is equal to 8.99 * 10^9 N*m²/C². Thirdly, ‘q1’ is equal to the charge in Coulomb’s (C) of the first object. As well, ‘q2’ is equal to the charge of the second object in Coulomb’s (C). Finally, ‘r²’ is equal to the radius between the two centres of the objects measured in metres, squared. The manipulated variable in this lab is the radius at which we place the metal sphere away from the pith ball. The responding variable is the electrostatic force of the pith ball as a result of the radius from the metal sphere. The controlled variable is the charge of the metal sphere, which is -3.59e-7C.

Equipment
1. Pith Ball
2. Metal Sphere: Has a charge of -3.59e-7C.
3. Spring Device: Measures force acting between the two spheres.

Procedure:
1. Make sure the pith ball is hanging insulated on the spring device, and that you have the metal sphere. 2. Carefully bring the metal sphere to a radius of 0.050m away from the pith ball (this can be done more precisely with a ruler). Hold it at that distance, then look at the spring device and write down the number it gives, which is equal to Force. 3. Repeat step two with the following distances between the pith ball’s centre to the metal sphere’s centre; 0.10m, 0.15m, 0.20m, 0.25m and 0.30m. Write down the force for each distance by looking at the spring device’s readings.

Pre-Lab Questions: (None were assigned.)

Observations:
Quantitative:
Trial
r(m)
Fe(N)
1
0.050
0.81
2
0.10
0.21...