Passage VII

When an ion moves through a uniform magnetic field, the ion follows a circular path having a radius R. A group of students conducted 3 studies to determine R under a variety of conditions for ions having the same mass.

The students used an apparatus consisting of an ion source, a metal plate with a hole in it, a power supply for generating various voltages between the ion source and the metal plate, and a movable charged-particle detector. Figure 1 shows the apparatus with the detector positioned to detect particular ions.

In each trial, the following occurred: Ions with the same electrical charge, Q, as well as the same mass were emitted by the ion source. The ions sped up, due to the voltage provided by the power supply, until they reached the hole in the plate. At the hole, their speed was V. After passing through the hole, they entered a uniform magnetic field of strength B. Under the influence of the field, they traveled along a circular path, still at speed V. The students moved the detector from side to side until it intercepted the ions and detected them. The students measured the distance between the hole in the metal plate and the ions' point of entry into the detector; R equaled this distance divided by 2.

Study 1

R was determined for ions having different V (see Table 1). Each ion had a Q of +1, and B equaled 0.10 Tesla (T).

Study 2

R was determined for ions having various Q (see Table 2). Each ion had a V of 7,500 m/sec, and B equaled 0.10 T.

Study 3

R was determined for various B (see Table 3). Each ion had a Q of +1 and a V of 7,500 m/sec.