In practice, we often have an unknown charge distribution and measure the electr

Question

In practice, we often have an unknown charge distribution and measure the electric field near it in order to determine the type of charge distribution. You have looked at Point charges, Dipoles, long lines of charge, and large flat sheets of charge.
At a distance of 6 cm you measure an electric field of 25000 N/C. At a distance of 24 cm you measure an electric field of 391 N/C. What is the charge distribution?
try this for help
a. Large Flat Sheet
b. Long straight rod
c.Point charge
d.Electric Dipole

Explanation / Answer

To do this, we must see the way the electric field falls off (decreases) with respect to the distance away from it.

((24 cm)/(6 cm))n = (391 N/C)/(25000 N/C)

==> n = log((391 N/C)/(25000 N/C))/log((24 cm)/(6 cm)) = -3

This implies that E is proportional to 1/r3

A large flat sheet has a uniform electric field (E is independed of r).

A long straight rod's electric field decreases as 1/r.

A point charge's electric field decreases as 1/r2.

Therefore, the answer is (d) since an electric dipole (E = kqd/r3) decreases as 1/r3.

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