A simple rail gun can be approximated by an RC circuit in which the resistor is
ID: 1528420 • Letter: A
Question
A simple rail gun can be approximated by an RC circuit in which the resistor is able to slide along two conducting rails (see picture). When the switch is thrown, a current flows from the capacitor around the circuit, thus creating a magnetic field (you may assume a large time constant for the circuit and treat the current as constant). The movable resistor feels a force due to this magnetic field and thus slides along the rails. Which direction does the resistor accelerate in, and why? If there is an induced electromotive force as the resistor slides, which direction does it point?
Conducting rail Movable resistor, can slide left or right. Conducting railExplanation / Answer
The direction of the current in the ciruit is clockwise. Using the Ampere's right hand rule, the direction of the magnetic field at the location of the resistor points into the page.
using the right rule, show the fingers of the right hand along the direction of the current, and curl them towards the magnetic field that is into the page. the streched thumb shows the direction of the magnetic force on the movable resistor that is towards right. therefore, the direction of the acceleration is towards right.
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