MDCAT Physics · Physics · Electromagnetism. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
A charge moving across a magnetic field feels a force at right angles to both its velocity and the field. A charge that is at rest, or moving parallel to the field, feels no force. Because the force is always at right angles to the motion, it does no work: the speed and kinetic energy stay the same and only the direction changes. So a charge entering at right angles moves in a circle.
This circular path is used to measure e/m for the electron.
A moving-coil galvanometer detects small currents. A low resistance (shunt) in parallel turns it into an ammeter. A high resistance in series turns it into a voltmeter.
Forgetting that the electron is negative. Find the force direction for a positive charge moving the same way, then reverse it.
Answer: A 1.0 Ω shunt connected in parallel with the galvanometer
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