# Thomson's Experiment and Charge to Mass Ratio

Thomson's Experiment: Instead of turning off the electric field to determine the charge-to mass ratio, Thomson proceeded to switch off the magnetic field. Suppose that the electric field is pointed towards the y-axis. Then, as the electron travels along the x-axis and hits the glass tube located say, L distance away from the source, the electrons will be deflected along y-axis by a distance, say D. By measuring D, from the knowledge of E,v, and L, Thomson could deduce an expression for e/me. Can you do the same?

Note: Use similar kinematical equations as projectile motion under gravity.

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#### Solution Preview

Force in y-direction, Fy = eE (direction -ve y-axis, because, electron has -ve charge, therefore, experiences a force opposite to direction of the field).

Therefore, acceleration ...

#### Solution Summary

An equation of e/m ratio for an electron is derived. Kinematic equations for projectile motion under gravity are used for the Thomson's Experiment. The solution is provided in a PDF and word document. The equations for the calculations are provided.