Lesson 9b: Special Relativity

1. Question: How does the electron's mass change with increasing energy?
   Answer: At low speeds, the mass doesn't change much with energy. At high speeds, the energy and the mass (measured in appropriate units) are equal to each other.

2. Question: How does the electron's speed change with increasing energy?
   Answer: At low energies, the speed increases as the square root of the energy. At high energies, the speed is pretty much constant (about the speed of light).