A Level Physics Practice Exam

In the context of ionization, what role do electrons play in a fluorescent tube?

1. They create ions through collision with vapor

2. They assist in light emission

3. They stabilize the ionized gas

4. They increase the potential difference

The correct answer is: They create ions through collision with vapor

Electrons in a fluorescent tube primarily play the role of creating ions through collisions with the gas vapor inside the tube. When the tube is energized, these free electrons are accelerated by the electric field established in the tube. As they move, they collide with the gas molecules (typically a low-pressure noble gas like neon or argon mixed with a small amount of mercury vapor). These collisions transfer energy to the gas atoms, leading to the ionization of some of them, meaning that they lose an electron and thus create positive ions. This process is crucial for maintaining the plasma state necessary for the tube to function and ultimately allows for the production of light. In addition to this, electrons do participate in the light emission, but this occurs after the ionization process. The electrons are also vital for maintaining the glow discharge and effectively facilitating the overall process, but their primary role at the moment of ionization is indeed to create ions through collision.