Lightning Strike

Your job was first to find two points with no (or very little) voltage between them. And then we asked you to find two points with high voltage between them.

You already know that along potential lines there is the same field strength, so there is the same energy level on one line. But there is only voltage if there is a difference in the energy level (potential) between two points. Because of this voltage between all points on one single potential line is always zero!

But you already know that there is an energy difference (potential difference) between different potential lines and so there is always voltage between those different lines. And the rule is: the bigger the difference of the field strengths between two points the bigger is the energy difference and the higher is the voltage between those two points.

If you move your cursor over the picture, you can see one possible solution. The points a and b are on the same potential line. Because of this point a and b have the same energy level. There is not energy difference between the two points and thus no voltage.
The points a and c, however, lie on different potential lines. This means that there is an energy difference between those lines and thus there is voltage between a and c.

Now, take a step back and think about the problem of the thunderbolt. Maybe you have an idea now under which circumstances a thunderbolt is particularly dangerous to a person.
Have you found the answer? Then it's only a little step to reach the solution!