1.6A: Field of a Point Charge
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It follows from equation 1.5.3 and the definition of electric field intensity that the electric field at a distance r from a point charge Q is of magnitude
E=Q4πϵ0r2.
This can be written in vector form:
E=Q4πϵ0r2ˆr=Q4πϵ0r3r.
Here ˆr is a unit vector in the radial direction, and r is a vector of length r in the radial direction.