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AP physics electromagnetism question?
An electron starts from rest 4.0cm from the center of a uniformly charged insulating sphere that has a total charge of 2nC. If the velocity of the electron is 1.5E7 m/s when it reaches the surface of the sphere, what's the radius of the sphere?
1 Answer
- Steve4PhysicsLv 76 years ago
If the radius of the sphere is R, the potential at a distance r from centre is V(r), where the (quite complicated) formula for V(r) is derived the link.
The potential at r=4cm (=0.04m) is V(0.04) and the potential at the surface is given by using the formula in the link by setting r=R.
Calculate the kinetic energy of the electron, which is (1/2)mv^2). This equals the potential energy lost which is |e(V(R) - V(0.04))|. This gives an equation you can then solve for R.