Example:
In the figure below, determine the point (other than at infinity) at which the total electric field strength is zero.
From the diagram, it can be observed that the point where E is zero lies on a straight line where the charges lie, to the left of the -2.5 μC charge.
Let this point be a distance r from the left charge.
Since the total electric field strength is zero,
E6μ = E-2μ
[6μ / (1 + r)2] / 4πεor2 = [2.5μ / r2] / 4πεor2 (Note: negative sign for -2.5 μC has been ignored here)
6 / (1 + r)2 = 2.5 / r2
√(6r) = 2.5 (1 + r)
r = 1.82 m
The point lies on a straight line where the charges lie, 1.82 m to the left of the -2.5 μC charge.
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