For an isotropic radiator, electric field intensity at a distance R is measured as 3 V/m. What will be the electric field intensity at a distance 3R ?

A

$$ 1 V/m $$

B

$$ \frac {1} {3} V/m $$

C

$$ \frac {1} {9} V/m $$

D

$$ 3 V/m$$