# Plot 2D electric field strength over distance (finite difference method)

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Even Nøtland Giske on 24 Feb 2021
Answered: Jaynik on 24 Jun 2024
Hello.
I am trying to 2D plot the electric field strength in kV/m over distance, like the figure below.
How do I do this?
My workspace is below, voltages are in a 181x301 matrix.

Jaynik on 24 Jun 2024
Hi Even,
The electric field strength can be approximated by the gradient of the voltage with respect to distance. Here is a sample code to plot the data:
% Calculate the electric field strength (V/km)
% Assuming the voltageMatrix rows represent different distances
% and columns represent different measurements at those distances
electricFieldStrength = diff(voltageMatrix, 1, 2) ./ diff(distance);
% Adjust the distance array to match the size of electricFieldStrength
distanceMidPoints = (distance(1:end-1) + distance(2:end)) / 2;
% Plotting
figure;
plot(distanceMidPoints, electricFieldStrength);
xlabel('Distance (km)');
ylabel('Electric Field Strength (V/km)');
title('Electric Field Strength vs. Distance');
grid on;
• The diff function computes the difference between adjacent elements. Here, it is used to approximate the gradient of the voltage with respect to distance.
• The result is divided by the distance difference to get the electric field strength in V/km.
• distanceMidPoints is calculated to align the x-axis values with the midpoints of the original distance intervals.
Hope this helps!