Physics 2 Lab

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Lab 201: Electric Field by Point Charges
Section: 121A-H02
Date: February 8, 2012

To compute electric field and corresponding field lines caused by point charges using MATLAB.

Theoretical Background:
-electrons are negative, protons are positive
-magnitude of force between A and B is:
, is 8.98755E9.
-electric field is the region around a charged object
-strength of electric field:
-electric field lines are used to visually show the field

Our procedure for this lab was very simple. We had to determine a correct MATLAB code to write. We inputted a code into MATLAB and received figure 1.1, the pot of the electric filed of a positive point charge. Our next goal was to plot the graph of the x position of a test charge in the presence of two positive charges versus the total electric filed at that point, we ended up with figure 1.2. We then repeated this plot, but with a positive and negative charge (figure 1.3). Lastly, we proceeded to plot the electric filed with two positive charges using a vector field plot (figure 1.4); and it was repeated for a positively and negatively charged particle in order to receive figure 1.5.


Figure 1.1

Figure 1.2

Figure 1.3

Figure 1.4

Figure 1.5

Part II

This was just copying code directly from the lab manual and seeing the results of the electric fields for various charged particles.


Part One Code:

clear all
esp0 = 8.85e-12;
k = 1/(4*pi*esp0);
q1 = 1e-9; %First Charge
q2 = -1e-9; %Second Charge
a = 1;
x = -2.1:0.1:2.1;
E1 = q1*k*(x+a)./abs(x+a).^3;
E2 = q2*k*(x-a)./abs(x-a).^3;
Etotal = E1 + E2;
plot(x, Etotal)
xlabel 'x'; ylabel 'Etotal';
grid on
title 'Total Electric field vs. x';

Part One Graph

Part Two Code:

[x, y] = meshgrid(-2.1:0.2:2.1, -2.1:0.2:2.1);
r1S = (x).^2 + (y-a).^2;
r1 = sqrt(r1S);
r2S = (x).^2 + (y+a).^2;
r2 = sqrt(r2S);
e1x = (x)./r1;
e1y = (y-a)./r1;
e2x = (x)./r2;
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