State what is meant by electric field strength.
Two point charges A and B are situated a distance 
apart in a vacuum, as illustrated in the figure below.
Point P lies on the line joining the charges and is a distance 
from charge A. The variation with distance of the electric field strength 
at point P is shown in the graph below.
By reference to the direction of the electric field, state and explain whether the charges A and B have the same, or opposite, signs.
State why, although charge A is a point charge, the electric field strength between 
and 
does not obey an inverse-square law.
Use the graph above to determine the ratio
.
