How is the charge of a particle determined in a cloud chamber?

The charge of a particle in a cloud chamber is determined by its curvature in a magnetic field.

A cloud chamber is a device that allows us to observe the paths of charged particles as they move through it. When a charged particle enters the chamber, it ionizes the gas molecules along its path, creating a trail of ions. These ions act as nuclei for water droplets to condense around, forming a visible track that can be photographed.

To determine the charge of a particle, the chamber is placed in a magnetic field. The magnetic field causes the charged particle to curve as it moves through the gas. The direction and curvature of the particle's path depend on its charge, mass, and velocity.

By measuring the radius of curvature of the particle's path, we can determine its charge-to-mass ratio. This is because the radius of curvature is proportional to the momentum of the particle, which is in turn proportional to its charge-to-mass ratio.

If we know the mass of the particle, we can then determine its charge. For example, if we observe a particle with a radius of curvature that corresponds to a charge-to-mass ratio of 1.6 x 10^-19 C/kg (the charge-to-mass ratio of an electron), we can conclude that the particle is an electron.

In summary, the charge of a particle in a cloud chamber is determined by observing its curvature in a magnetic field and using the charge-to-mass ratio to calculate its charge.