The photograph shows the trajectories that an electron beam follows when it moves through a uniform magnetic field. The tube contains a small amount of mercury gas that is used to make the electron beam visible. Electrons are accelerated by a potential difference applied between two plates and they collide with the gas atoms emitting a characteristic green light. When the velocity of the charged particles is perpendicular to the uniform magnetic field, they experience a magnetic force that makes them move in a circular path (left side). However, if the direction of the velocity of the beam is at some arbitrary angle, the charged particles describe a helix (right side).

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Sergio Andrés Joya
Vanier College, Montreal, Quebec
Third Prize ( High School Individual Category )

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