Theory

**Coulomb's Law: **It refers to forces that are exerted
between __point electric charges__, that have:*
Strength*, given by the equation: F=kQq/r

Activities

On the left figure you see
a charge in the center, and a test (black) charge, q=10^{-9}C. If you
move the test charge with the mouse, you will notice on the right figure, the
force exerted by the central charge on the test charge. You can change the
central charge or even show the vector of the force.

**Question:** Can you use the figures to realize whether the force
is atractive or repulsive;

**Exercise:** Can you calculate the strength of the central charge? *( hint:
drag the test charge to a distance eg. 1m,count the force on the figure and
calculate the central charge)*