Earth's Magnetic Field with Electron orbit

[hellsingfan]

Homework Statement

High above the surface of the Earth, charged particles (such as electrons and protons) can become trapped in the Earth's magnetic field in regions known as Van Allen belts. A typical electron in a Van Allen belt has an energy of 55 keV and travels in a roughly circular orbit with an average radius of 240 m. What is the magnitude of the Earth's magnetic field where such an electron orbits?

Homework Equations

Don't know. I don't see any equation to relates energy to magnetism.

The Attempt at a Solution

Don't even know where to begin

Please help.

Thank You

 

[hellsingfan]

nevermind figured it out...