They discovered that, when an electron collided with a mercury atom, it could lose only a specific quantity (4.9 electron volts) of its kinetic energy, which corresponds to decelerating the electron from a speed of about 1.3 million meters per second to zero.
It could lose only a specific quantity (4.9 electron volts) of its kinetic energy. An electron collided with a mercury atom. They discovered this. Its kinetic energy corresponds to decelerating the electron from a speed of about 1.3 million meters per second to zero.