In order to estimate the properties of a uniform magnetic field, you shoot an al

Question

In order to estimate the properties of a uniform magnetic field, you shoot an alpha particle into the field. The alpha particle has an initial speed of 1.7 x 10^7 m/s. The initial trajectory, moving horizontally from left to right, is set so that it will enter the magnetic field directly in front of you. After entering the field, the alpha particle moves in a counterclockwise orbit with a diameter of 25.4 cm in a vertical plane. What does this tell us about the field? (Alpha particles carry q = +2e charge and the mass is m = 6.6 10-27 kg)

direction:

vertical, upward

horizontal, toward the observer

vertical, downward

horizontal, away from the observer

magnitude: T ?

Explanation / Answer

Direction: vertical, upward.

Now, magnetic force = centrifugal force

v * B * 2e = mv^2/r

B = m * v /(2 * e * r)

= 6.6 * 10^-27 * 1.7 * 10^7 / (2 * 1.6 * 10^-19 * 0.127)

= 2.761 T

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