# What are the limits of Coulomb's law

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### Field of a charged sphere (Coulomb field)

In order to get a qualitative statement about the field strength around a charged sphere, one can measure the force that it exerts on a test charge.

In the following projects, the Coulomb law for the force between two point-shaped or spherical charges is worked out. The aim is to get to know the dependence of the force on the distance and charge of the balls and thus to be able to make predictions about the force on a test charge in the field of other charges.

JPAKMA project: Coulomb field - variation of the charge

Work order

Two charged, spherical bodies at a fixed distance from each other are considered. Statements should be made about the forces acting - depending on the charges on the two balls. The forces acting on the two balls are drawn as force arrows.

• Vary the charges of the two balls and consider the forces that arise.
• What influence do the charges have if their signs are the same or different?
• How do the forces change when one of the two charges is halved, doubled or otherwise multiplied? Formulate the dependence of the force on the left and the right charge.
• Why do the same forces act on both spheres, even if their charges are completely different?

JPAKMA project: Coulomb field - variation of the distance

Work order

Two charged, spherical bodies are considered. The right ball can be moved using the slider. The force that acts on the right ball from the electric field of the left (fixed) ball is shown as a force arrow and in the graph of the - diagram.

Slowly move the right ball back and forth as far as it will go and interpret the resulting force-distance graph. What kind of analytical connection can be assumed between force and distance?