PhysicsLAB: Coulomb's Law: Suspended Spheres

This example blends electrostatics, freebody diagrams, equilibrium conditions, and basic right triangle trigonometry.

Refer to the following information for the next seven questions.

In this example we will examine two identical spheres each of mass 5 grams and charge q that are suspended from two light uncharged, nonconducting threads of length 40 cm. Each string makes an angle of 15º with the vertical.

Our ultimate task will be to calculate the charge on each sphere.

	Draw a freebody diagram showing the forces that act on the right sphere.

	Calculate the weight of each sphere.

	Develop an expression for the repulsive electrostatic force on the sphere.

	Since are spheres are in equilibrium, write the expression for net F_x = 0.

	Since are spheres are in equilibrium, write the expression for net F_y = 0.

	What is the magnitude of the tension in the string?

	What is the magnitude of the charge on each sphere?