In a mass-flight spectrometer, the source emits a bunch of charged particles that first fly freely and pass through the first sensor D₁, located at a distance L from the grid. Behind the grid, along the normal to it, an electric force F acts on the particles. The particles turn and fly back through the grid, passing through the second sensor D₂, which is located at the same distance from the grid. The speed of the outgoing particles depends on the source voltage, but its exact value remains unknown. Changing the voltage, measure the time between sensor responses and find its smallest value ∆t. What is the mass of the particle? How can one find the mass of particles if the source emits several varieties of particles with different masses?