An isloated point charge produce an electric field with magnitude E at a point 2 m away. At a point 1 m from the charge magnitude of the charge is .. A. E B. 2E C. 4E D. E/2

the correct answer is C,      E’= 4E

Explanation:

In this exercise you are asked to calculate the electric field at a given point

         E =

indicates that the field is E for r = 2m

         E =                  (1)

the field is requested for a distance r = 1 m

         E ’= k \frac{q}{r'^2}

         E ’= k q / 1

from equation 1

         4E = k q

we substitute

        E’= 4E

so the correct answer is C

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