How an electron moves in electric and magnetic fields, the velocity selector, Millikan's force balance that proved charge is quantised, and Thomson's crossed-field measurement of e/m.
Unit 6 carries 12 of the 50 physics marks — the heaviest unit in the subject — and with seven chapters sharing them, this one averages a little under two (MEC publishes weights by unit, not by chapter). The two experiments in it, Thomson's and Millikan's, between them fix the electron's charge and its mass, so they are also the arithmetic behind every other chapter of the unit.
The MEC scope lines are: Motion of an electron in electric and magnetic fields; Millikan's oil-drop experiment; J. J. Thomson's experiment. The headings below are those three points, in MEC's order.
Three ways it is asked: recall (the value of e/m, the properties of cathode rays, what Millikan's experiment proved, Millikan's assumptions); understanding (why a magnetic field changes an electron's direction but not its speed, why the velocity selector does not care about the particle's mass, why oil and not water); application (a radius or a period in a magnetic field, a deflection on a screen, a charge on a balanced drop, an e/m from crossed-field data).
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