Two point charges A and B are separated by a distance of 
in a vacuum, as illustrated in the figure below.
A point P is a distance 
from A along the line AB. The variation with distance of the electric potential 
due to charge A alone is shown in the graph below.
The variation with distance of the electric potential 
due to charge B alone is also shown in the graph above.
State and explain whether the charges A and B are of the same, or opposite, sign.
By reference to the graph above, state how the combined electric potential due to both charges may be determined.
Without any calculation, use the graph above to estimate the distance at which the combined electric potential of the two charges is a minimum.
The point P is a distance 
from A. An 
-particle has kinetic energy 
when at infinity. Use the graph above to determine the minimum value of such that the -particle may travel from infinity to point P.
to 
.
.
