J.J. Thomson's cathode ray experiment - The WikiPremed MCAT Course

Get to know the experiments which were instrumental in the history of science, because variations often show up in MCAT passages. The experiments of early modern physics that illuminated the nature of the atom, for example, are ideal for MCAT passages because they not only lead to questions dealing with atomic theory, they are also good sources for questions on more basic physics.

As an example, think about the free body diagram describing the forces on an electron in J.J. Thompson's cathode ray experiment. Both magnetic force and electrostatic force are involved. The experiment produced conclusions for early Atomic Thoery. From an MCAT writer's perspective, this is a fruitful variety, ideal for an MCAT passage.

In the cathode ray experiment, when the beam of electrons passes through the cathode ray apparatus on a straight line (no deflection) the magnetic and electrostatic forces on a particular electron are in equilibrium. This force equilibrium is the key relationship which allowed Thompson to formulate an equation which could then lead to the charge to mass ratio of the electron.

The WikiPremed MCAT Course is a free comprehensive course in the undergraduate level general sciences. Undergraduate level physics, chemistry, organic chemistry and biology are presented by this course as a unified whole within a spiraling curriculum.

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