Force on Moving Charges & Right Hand Rule Video Lessons

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Problem: In the late 19th century, great interest was directed toward the study of electrical discharges in gases and the nature of so-called cathode rays. One remarkable series of experiments with cathode rays, conducted by J. J. Thomson around 1897, led to the discovery of the electron.With the idea that cathode rays were charged particles, Thomson used a cathode-ray tube to measure the ratio of charge to mass, q/m, of these particles, repeating the measurements with different cathode materials and different residual gases in the tube.Now suppose you carry out a second Thomson experiment with a different beam that contains two types of particles. In particular, both types have the same mass m as an electron, but one has charge e and the other has charge 2e. The beam is filtered, such that both types of particle have the same speed. As in the previous experiment, initially only the electric field is imposed and the deflection of the beam is observed as a spot on the screen; then, in the second phase of the experiment, one attempts to tune the magnetic field to exactly cancel the effect of the electric field.What would you observe on the screen during this experiment?(a) Two off-centered spots in both the first and the second phases of the experiment(b) Two off-centered spots in the first phase of the experiment; one centered spot in the second phase of the experiment(c) Two off-centered spots in the first phase of the experiment; one centered and one off-centered spot in the second phase of the experiment(d) One off-centered spot in the first phase of the experiment; one centered and one off-centered spot in the second phase of the experiment(d) One off-centered spot in the first phase of the experiment; two off-centered spots in the second phase of the experiment(e) One off-centered spot in both the first and the second phases of the experiment

FREE Expert Solution

Vertical acceleration, ay = eE/m.

The two particles will accelerate differently in the first part leading to two spots away from the center.

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Problem Details

In the late 19th century, great interest was directed toward the study of electrical discharges in gases and the nature of so-called cathode rays. One remarkable series of experiments with cathode rays, conducted by J. J. Thomson around 1897, led to the discovery of the electron.

With the idea that cathode rays were charged particles, Thomson used a cathode-ray tube to measure the ratio of charge to mass, q/m, of these particles, repeating the measurements with different cathode materials and different residual gases in the tube.


Now suppose you carry out a second Thomson experiment with a different beam that contains two types of particles. In particular, both types have the same mass m as an electron, but one has charge e and the other has charge 2e. The beam is filtered, such that both types of particle have the same speed. As in the previous experiment, initially only the electric field is imposed and the deflection of the beam is observed as a spot on the screen; then, in the second phase of the experiment, one attempts to tune the magnetic field to exactly cancel the effect of the electric field.

What would you observe on the screen during this experiment?

(a) Two off-centered spots in both the first and the second phases of the experiment

(b) Two off-centered spots in the first phase of the experiment; one centered spot in the second phase of the experiment

(c) Two off-centered spots in the first phase of the experiment; one centered and one off-centered spot in the second phase of the experiment

(d) One off-centered spot in the first phase of the experiment; one centered and one off-centered spot in the second phase of the experiment

(d) One off-centered spot in the first phase of the experiment; two off-centered spots in the second phase of the experiment

(e) One off-centered spot in both the first and the second phases of the experiment

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