Electric Field from a Point Charge

Consider the electric force equations

F = kq1q2/r**2

F = (1/4peo) q1q2 /r**2

and

F = E q2

we can see that

E = kq1/r**2

or

E = (1/4peo) q1/r**2

compare with the equation for g from a point mass

g=Gm/r**2

Note:
E
compares with
g
k
compares with
G
q
compares with
m
Symbol
Description
Units
E
the electric field strength
N/C
k

The Coulomb constant

8.99 x 10**9
Nm**2C**-2
eo

Permittivity of Free Space

8.85 10**-12

(not to be confused with permeability of free space which applies to magnetism)
C**2N**-1m**-2
q
Electric charge
C
r
distance from centre of charge to the point that the E strength is being determined
m

IB Physics Home