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7.8: Moving-coil Ammeter

  • Page ID
    5788
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    Figure 7.5.png
    \(\text{FIGURE VII.5}\)

    The current is led into the coil of \(N\) turns through a spiral spring of torsion constant \(c\). The coil is between two poles of a specially-shaped magnet, and there is an iron cylinder inside the coil. This ensures that the magnetic field is everywhere parallel to the plane of the coil; that is, at right angles to its magnetic moment vector. This ensures that the deflection of the coil increases linearly with current, for there is no \(\sin \theta\) factor. When a current flows through the coil, the torque on it is \(NABI\), and this in counteracted by the torque \(c\theta\) of the holding springs. Thus the current and deflection are related by

    \[NABI = c\theta.\]


    This page titled 7.8: Moving-coil Ammeter is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by Jeremy Tatum via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.